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A portable paper-based enzyme-linked biosensor that integrates a multi-enzyme cascade reaction, natural enzyme, and nanozyme with filter paper, combined with smartphones, is proposed for the detection of xanthine (XA) and sarcosine (SA) in urine. The primary biological component of the sensor is horseradish peroxidase (HRP). By chemically modifying cellulose filter paper (CFP) the HRP in horseradish crude extract is specifically immobilized through boron affinity and metal chelation techniques. Furthermore, the incorporation of UiO-66 on CFP had a good synergistic effect on the electron transfer of HRP and the detection of H 2 O 2 , significantly increasing the sensor's sensitivity. Under optimized experimental conditions, the sensor demonstrated a dynamic response range of 8–400 μmol L−1 for SA with a minimum detection limit (LOD) of 5 μmol L−1, and a dynamic response range of 10–400 μmol L−1 with an LOD of 8 μmol L−1 for XA. Additionally, the well-designed detection area of the portable test strip simplifies the detection operation, reduces the detection time, and enables rapid on-site analysis. UV-Vis analysis further confirmed the sensor's accuracy in detecting disease markers in urine. The sensing platform has good reproducibility, specificity and stability, suitable for the detection of SA and XA in real human urine samples, and the sensor has the advantages of simple manufacturing, easy operation, strong portability, low reagent consumption, and low cost benefit. Therefore, the development of this paper-based enzyme-linked biosensor offers a novel approach to the detection of disease markers in urine and has potential applications in medical testing. [Display omitted] • Paper-based enzyme-linked biosensor was successfully prepared. • Smartphone-assisted test paper detected xanthine and sarcosine in urine. • The sensor immobilizes HRP from horseradish by modifying the filter paper. • The addition of UiO-66 had good synergistic effect on the HRP's electron transfer. • The portable test paper can realize the simultaneous detection of multiple copies. [ABSTRACT FROM AUTHOR]

Increased evaporative losses and flow obstructions can present substantial impediments to current paper analytical devices (µPADs) for efficient on-site testing of biological fluids. Strategic enhancements in wicking rates of paper may thereby counter these limitations and enable on-demand healthcare monitoring. Therefore, herein we have leveraged the features of paper fold-crease regions and developed a novel fast-flowing platform using laser printing to accelerate fluid flow through paper. A series of extensive experiments have been conducted to optimize the design and maximize wicking rates of µPADs for smaller liquid volumes, making it well-suited for analysing biofluids. The investigation delves into structural alterations within the creased regions, employing both static and dynamic force application strategies. A first-generation Washburn type model in excellent agreement with the experimental findings is developed, providing a comprehensive insight into the fundamental physics involved. Finally, the folded channels are utilized for a distance-based hematocrit sensor employing grade-1 filter paper at very low-cost, simplified fabrication, lesser sample volume and faster analysis. The findings of this work unveil a plethora of potentialities for employing paper and paper folds to develop affordable medical devices with advanced analytical functionalities, specifically tailored for the resource-constrained settings. [Display omitted] • An innovative method to accelerate smaller fluid volumes is proposed by exploiting fold and creased areas of paper. • Mathematical model modifying Lucas-Washburn equation is developed providing insights into physics of rapid flow. • Developed devices are employed for accurately measuring blood hematocrit at significantly low cost and testing time. • The devices precisely differentiate Hct ranges with 90.74 % sensitivity when validated with a commercial haematocytometer. [ABSTRACT FROM AUTHOR]

This work describes a direct optical readout of an ion-selective potentiometric sensing array without an external power supply. Electronic paper (e-paper) was chosen as the signal transducer owing to its fast response on the order of seconds and its wide dynamic range of about 1.5 V. The capacitive character of the display allows one to observe the optical response at zero current, which is a desired condition for the potentiometric measurement. An applied potential of 1 V gives a transient charge flow of about 11 μC for the e-paper to exhibit a maximal intensity change. The cathodes of three different pixels of the e-paper were connected to three different ISEs responsive to Na+, K+, and Ca2+, while their common anode was connected to the shared reference electrode (RE). In this manner, each pixel is mapped to the behavior of one sensor, making it possible to detect multiple ions with an e-pixel array. The sensor configuration gave quantitative information on Na+, K+, and Ca2+ from 10−5 M to 10−1 M by analyzing the RGB information of the pixels. The e-paper exhibited a stable response within half a minute, much faster than previously established electrochromic material transducers such as Prussian Blue (PB). With this approach we successfully carried out multi-ion concentration sensing without external power, which is potentially attractive for applications in environmental monitoring, clinical assays and wearable sensing devices. [Display omitted] • A self-powered multi-channel potentiometric sensor array for simultaneous monitoring of potassium, calcium, and sodium. • The rapid optical response of this sensor is adequate for real time monitoring. • Excellent correlation between this approach and direct potentiometry. [ABSTRACT FROM AUTHOR]

Branched-chain amino acids (BCAAs) are essential amino acids that play a crucial role in regulating animal physiology and metabolism. The lack of sensitive, rapid, and portable methods for measuring BCAA concentrations in blood samples hinders precise and dynamic monitoring of nutritional status during swine production. In this work, a paper-based analytical device (PAD) was developed for quantifying BCAAs in blood samples. The device utilized a redox reaction between BCAAs and NAD+ catalyzed by leucine dehydrogenase, producing NADH that could be detected by NADH-responsive polymer dots with high selectivity, sensitivity, and accuracy. A separation membrane was incorporated in the PAD for spontaneous blood-plasma separation. The fluorescent images were captured by using a smartphone. It required only 20 μL of blood volume, and the entire assay could be completed in less than 5 minutes. The quantitation range spanned from 35 μM to 1000 μM, covering the normal BCAA concentration range in porcine bloods. The BCAA concentration measured with the PAD assay was in good agreement with those obtained with an ELISA kit. In sum, this PAD-based BCAA assay offers a point-of-care testing approach for monitoring BCAA levels in pig production, especially with a low-protein diet. • A portable paper-based analytical device was developed for BCAAs quantification. • The NADH-sensitive polymer dots were utilized as the ratiometric fluorescent probe. • A ratiometric fluorescent assay was achieved by using a smartphone. • Total BCAA level in pig blood was accurately determined. [ABSTRACT FROM AUTHOR]

This article introduces the first demonstration of integrating distance-based paper analytical devices (dPADs) with ionic liquid-based dispersive liquid-liquid microextraction (IL-DLLME) for the quantitative detection of bilirubin levels in human samples. In this approach, bilirubin is preconcentrated and extracted into a small droplet of the extraction solvent using IL-DLLME. The resulting solution is then introduced into an economical and straightforward dPAD sensor. Detection relies on a colorimetric reaction between bilirubin and gold ions (Au3+), leading to the in-situ formation of gold nanoparticles (AuNPs) on the paper substrate. The observed red-purple distance length is directly proportional to the bilirubin level. Under optimization, a linear range between 0.25 nM and 5.0 nM (R2 = 0.9979) and a detection limit (LOD) of 250.0 pM were achieved. The assay exhibits notable precision and selectivity without any interference. With its distance readout feature, this method is simpler and more cost-effective, offering greater sensitivity compared to other methods requiring expensive reagents and instruments. Moreover, the technique shows high accuracy and precision for bilirubin quantification in human control samples, with recoveries ranging from 98.33% to 102.00%. No significant difference was observed between our method and the enzyme-linked immunoassay (ELISA) method. By combining a low-cost microfluidic device with a simple microextraction method, this strategy holds great potential as an alternative analytical method for determining bilirubin. It can be expanded for further applications in analytical sensing for point-of-care (POC) diagnostics. [Display omitted] • We introduce the combination of the simple dPADs with IL-DLLME for enzyme-free quantification of bilirubin. • Bilirubin is rapidly extracted and preconcentrated and reacted with Au3+ reagent on paper substrate. • Detection limit of 250.0 pM was obtained without requirement of the expensive reagents and instruments. • The analytical performance is well-suited for bilirubin detection in human samples. [ABSTRACT FROM AUTHOR]

Early detection and analysis of pathogens in food are an effective way to curb food poisoning. Traditional detection methods require complex sample pretreament and high costs, and are not easy to implement point-of-care testing (POCT) for food safety. By preparing a patch of vitrified silk fibroin hollow microneedle array patch (SF-HMAP) and integrating it with a patterned paper-based chip using a 3D printing technology and a double-printed die fabrication process, a conceptual sensor in the form of a microneedle array paper chip has been successfully developed. During the preparation of the sensor, the vitrified SF-HMAP with a suitable diameter and height exhibits a complete and homogeneous structure and excellent mechanical properties, thus being able to meet the puncture detection of various food products. Meanwhile, rice paper with good color intensity and uniformity was selected as the patterned paper-based chip sensing layer and assembled with vitrified SF-HMAP to form a sensor, which can quickly absorb and transmit liquid into the solid gel within 9 min. To validate the practicality of the conceptual sensor, the loading of copper nanoclusters (Cu NCs) probes in a patterned paper-based sensing layer enabled continuous visual fluorescence monitoring of histamine produced during the storage of fresh pork and fresh shrimp and color comparison with standard colorimetric cards for histamine detection, allowing semi-quantitative colorimetric detection of histamine in actual samples. The proposed portable conceptual sensor is adjustable and versatile, and offers a novel idea and approach for food safety detection. • A portable colorimetric sensor for histamine was prepared based on paper chip. • The conceptual sensor was validated for raw meat-mimic environment. • The sensor enables continuous monitoring of histamine in pork and shrimp. • The sensor promises to be a powerful tool for point-of-care testing of food safety. [ABSTRACT FROM AUTHOR]

Label-free electrochemical sensors have gained popularity as point-of-care devices because they do not require complicated labeling procedures. However, they have difficulties detecting multiple analytes simultaneously. In this study, we developed a novel label-free electrochemical immunosensor on an origami paper–based analytical device (oPAD) for the simultaneous detection of quinolone antibiotics, in which norfloxacin (Nor) and enrofloxacin (Enr) were used as a model. The oPAD was designed with two antibody zones, each zone contains different antibodies. The oPAD has two thionine- and ferrocenecarboxylic acid-coated reagent zones, as redox species, which will generate the response current signals for the detection of quinolone antibiotics. The simultaneous current responses of thionine and ferrocenecarboxylic acid decreased proportionately when exposed to Nor and Enr concentrations, respectively. Under optimal conditions, this device provided linear range at concentrations of 0.01–10 µg/mL for the detection of Nor and Enr and limit of detection was calculated as 2.02 and 1.70 ng/mL, respectively. Moreover, this device demonstrates performance comparable to standard methods for the simultaneous detection of Nor and Enr in milk, honey, and fish. Therefore, label-free electrochemical immunosensors provide a highly potent, inexpensive, and portable method for detecting multiple quinolone antibiotics simultaneously on a single device. [Display omitted] • Origami immunosensor was developed for simultaneous detection without labeling. • The oPAD can specifically analyze quinolone residues at the ng/mL level. • Norfloxacin and enrofloxacin in real food samples are accurately estimated. [ABSTRACT FROM AUTHOR]

In this study, we report the development of a paper-based platform with low amount of reagents for the detection of the histidine-rich protein 2 by an enzyme-based colorimetric assay aiming for the early diagnosis of Plasmodium falciparum malaria. A CO 2 laser cutter was used for the fabrication of the device in a simple layout suitable to perform the lateral flow assay, which consisted in a region for sample addition, a detection zone and an absorbent pad, all of which were linked by microfluidic channels. Investigations related to the performance of the sandwich immunoassay in the nitrocellulose membrane shown that the blocking and washing steps are essential to promote efficient antigen-antibody recognition and to generate reliable results, avoiding misinterpretations. Several parameters were also evaluated and the experimental conditions were optimized: concentration and incubation time with the capture antibody (50 μg mL −1 and 5 min, respectively); BSA solution at 1.5% (w/v) containing 0.1% (v/v) Tween 20 for blocking the nitrocellulose and 10 min as the incubation time; 10 mmol L −1 Tris-HCl buffer solution at pH 7.4 containing 0.15 mol L −1 NaCl and 0.1% (v/v) Tween 20 for washing the device before adding the ready to use TMB substrate at the detection zone. The system demonstrated a good sensitivity and detectability reaching a visual and calculated limit of detection of 5.0 ng mL −1 (65 parasites μL −1 ) and 4.5 ng mL −1 (59 parasites μL −1 ) respectively, a clinically relevant concentration that should be sufficient to identify the disease in the appearance of the first symptoms and with the advantage of not needing to use nanostructures or other strategy for signal amplification beyond the enzyme. [ABSTRACT FROM AUTHOR]

Paper-based microfluidic chips have shown great potential for use in rapid clinical diagnostics. In this work, we present a paper-based device that integrates an electromagnetically actuated valve and an adjustable time controller for the simultaneous detection of multiple tumor biomarkers. The time controller consists of a timing channel and two movable conductive iron bands that function as an electric switch. Once the conductive iron bands are connected by the fluid flow, the circuit would be closed to actuate the magnetic valve, initiating chemiluminiscent immunoassay (CLIA) reactions. Using a HRP- O -phenylenediamine-H 2 O 2 detection system, simultaneous detection of different concentrations of carcinoembryonic antigens (CEA) was demonstrated. The resulting CLIA peak intensity exhibited a good linear relationship with the logarithm of the CEA concentration from 0.1–80 ng mL −1 . Further experiments showed that the developed device was capable of detecting multiple tumor biomarkers simultaneously. We can program different incubation times for the detection of different biomarkers by moving the conductive bands on this paper-based device. In this study, only 16 min was required to complete CEA detection. This strategy greatly shortens detection time compared to the conventional chemiluminiscence technique for CEA detection (nearly 2 h). This paper-based device provides a simple and inexpensive platform for immunoassay-based detection of disease-related biomarkers. [ABSTRACT FROM AUTHOR]

Starch gelatinization is pivotal in food processing, impacting viscosity, texture, and functionality. However, current methods for determining concentration and viscosity of gelatinized starch (GS), such as falling ball and rotational viscometers, are impractical for in situ measurements due to bulky equipment. Here, we introduce a paper-based radial chromatographic assay (PRCA) method for rapidly measuring the concentration of gelatinized starch (GS). We utilized Evans Blue (EB) as a chromatic agent to label GS and generate color-ring patterns on a nitrocellulose membrane based on the "Coffee-ring" effect. The resulting PRCA patterns varied depending on the GS concentrations, yielding a good linear correlation (R2 > 0.967) between grayscale value and viscosity. This method enables rapid measurement of GS concentration within 10 s, even with varying ratios of amylose to amylopectin. PRCA demonstrates a detection limit for GS concentration between 0.027 % and 0.051 %, which is 10-20 fold lower than that of traditional rotational-viscometer. The intensity of PRCA patterns at pH 3 (45.8) was significantly lower than those at higher pH levels (5 to 9), consistent with the decreased viscosity measured by the viscosimeter. The intensity of PRCA patterns did not change with increasing temperature from 25°C to 90°C, despite the significant decrease in viscosity from 345 mPa•s to 195 mPa•s. Additionally, PRCA can monitor changes in starch viscosity during the hydrolysis process, which decreases from 744 mPa•s to 6 mPa•s. This capability provides an efficient means of measuring the concentration and viscosity of GS during food processing. • A paper-based method for in-situ measurement of starch paste viscosity was successfully developed. • The intensity of the color-ring pattern was highly correlated with starch viscosity. • This method is capable of quantitatively measuring starch viscosity within 10 s • This method exhibited lower LOD and LOQ than traditional rotation-viscometer. [ABSTRACT FROM AUTHOR]

Molecularly imprinted polymer (MIP-QDs) with fluorescence quenching ability toward propazine was synthesized for propazine detection. b(Blue)-MIP-QDs were prepared using ZnCdS/ZnS QDs via reverse micro-emulsion, whereas r(red)-MIP-QDs were synthesized using CdSe/ZnS QDs. By utilizing graphene quantum dots (GQDs) as a stable fluorescence intensity reference, the wide-gamut fluorescence test paper was constructed on the basis of mixing b-MIP-QDs, r-MIP-QDs, and GQDs under the optimal ratio. When analyzing spiked propazine in fish and seawater samples using a test paper, satisfactory recoveries of 104.0 %–114.6 % and 92.0 %–96.4 % were obtained, with corresponding limits of detection of 5.0 μg/kg and 1.0 μg/L, respectively. The RGB extractor was utilized to extract the actual fluorescence color and construct a dataset consisting of R, G, and B values, as well as concentration data from 400 samples. The SVR model of Python 3.9.7 was used to obtain and analyze the concentration and feature data. After optimization, the constructed model achieved a correlation coefficient of 0.98 and an RMSE of only 1.81, indicating high prediction accuracy and excellent generalization ability that meet quenching prediction requirements. As an intelligent and rapid detection method, this model holds significant practical significance. [Display omitted] • A wide-gamut fluorescence visual test paper was fabricated. • The visual test paper demonstrates excellent linearity, accuracy, precision, and sensitivity for promazine detect. • An RGB model by support vector machine were constructed. • The model exhibits high accuracy and strong generalization ability. [ABSTRACT FROM AUTHOR]

Flexible humidity sensors have been widely used in wearable electronics, owing to their flexibility and compatibility with electronic device substrates. This study fabricated a flexible paper-based humidity sensor with a grid-like sensing film using the near-field electrohydrodynamic direct writing (NFEDW) method. A grid-like sensing layer with a dense network of carbon nanotubes/cellulose nanofiber (CNTs/CNF) was prepared, and induced by a voltage field applied during printing. The effects of the substrates and pattern width on the performance of the sensor were systematically investigated. The prepared sensor exhibited high sensitivity of 101 % at 95 % relative humidity (RH). An interlocking structure formed between the CNTs/CNF composite and the paper substrate, endowing the sensor with outstanding bending (minimum diameter of 5 mm) and folding (up to 100 times) durability. Furthermore, the prepared sensor exhibited rapid response performance (17 % within 10 s). This addresses the issue of long response time, which is typically associated with CNTs-based sensors, making these sensors more suitable to practical applications. The above-mentioned advantages enable the sensor to be used for respiration monitoring and even for vocal recognition. Finally, a real-time respiration monitoring platform was developed to demonstrate the sensor's potential in wearable devices. • The high precision printing method is used for preparing the sensing film. • Various pattern widths are achieved by altering printing height. • Printing paper as the substrate to improve the performance of the sensor. • Substantially improved response time for the CNT-based sensors. • Wireless monitoring platform is developed for real-time respiration monitoring. [ABSTRACT FROM AUTHOR]

Biohazards, which may occur at all supply chain stages, pose significant threats to food safety and public health. Addressing these concerns and enhancing food safety necessitates a nondestructive pathogen surveillance approach capable of continuously and simultaneously detecting multiple pathogens. Detecting and differentiating low concentrations of pathogenic bacteria amid high background microflora levels in foods is challenging, requiring technology with high sensitivity and robust discriminatory capability. This study introduces an artificial neural network-driven paper chromogenic array sensor (ANN-PCA) technique developed for the nondestructive, continuous, and simultaneous detection of Salmonella Enteritidis (SE) and Escherichia coli O157:H7 (Ec) from a high background microflora in shredded cheddar cheese. This method enables accurate detection of SE and Ec in monoculture and cocktail culture while distinguishing them from a high level of background microflora (∼7.5 log CFU/g), with accuracies ranging from 72 ± 11% to 92 ± 3%. In addition, SE and Ec were successfully identified at concentrations as low as 1 log CFU/g within one day, with an accuracy of 72 ± 11%. This approach exhibits promising potential for integration into a digitalized, smart, and resilient nondestructive surveillance system for real-time pathogen detection in foods throughout the supply chain without enrichment, incubation, or other sample preparation steps. [Display omitted] • Development of a machine learning-driven paper chromogenic array sensor approach. • Non-destructive, continuous, and simultaneous detection of multiple pathogens. • Detection of pathogenic bacteria from a high level of background microflora. • The approach provided potential detection for pathogens throughout the food supply chain. [ABSTRACT FROM AUTHOR]

The development of smartphone electronics and the prevalence of quick response (QR) codes make them valuable tools for digitizing and decentralizing tests to fields and households. Now there is a growing trend for adapting them into sensing and diagnostic needs from paper microfluidics. Herein, we show a new QR-coded microfluidic paper-based analytical device (QR-coded μPAD) consisting of stacked layers of printed QR code, transparency film, and microfluidically patterned paper. It combines multichannel colorimetric sensing with QR code generation into smartphone-based multiplexed assays with the aid of gray patterns on the transparency film. The QR-coded μPAD paired with an accompanying mobile application is successfully applied to simultaneous implementation of beverage/aquatic tests and QR code functions. Our QR code conversion strategy provides the superb flexibility and compatibility for paper microfluidics of various designs. The work suggests that our versatile integration of paper microfluidics, smartphone science, and QR code uses can make rapid, interactive, and automated on-site testing and reporting, leading to opportunities to advance the development of smart paper microfluidics. [Display omitted] • A versatile QR code conversion strategy for paper microfluidics was proposed. • Stacked layer design and printed gray patterns hold the key to device fabrication. • Simultaneous implementation of analyte analysis and QR code functions in one scan. • Our QR-coded μPADs were applied into beverage tests and water quality monitoring. [ABSTRACT FROM AUTHOR]

Microfluidic paper-based analytical devices (mPADs) have gained significant attention in recent years for applications ranging from clinical diagnostics to environmental testing. However, separation on mPADs remains challenging to implement, particularly in complex samples. This has revived interest in revisiting paper chromatography and paper electrophoresis in mPADs to address these needs. Here, laminated Parafilm-paper (l-paper) is applied to fabricate electrophoretic devices. This approach yields a free-standing channel, leading to improved peak resolution relative to previous electrophoretic separations in traditional wax-printed mPADs. Major factors influencing the separation, including Joule heating, electroosmotic flow, and electrophoretic mobility, were investigated. As a result of paper’s high ratio of surface area (78%) to pore volume (22%) resulting in slow heat dissipation, a usable applied field strength range of 0–200 V cm −1 was employed to avoid Joule heating. The electroosmotic flow of the system was found to be 2.5 × 10 −5 ± 7.7 × 10 −7  cm 2 V −1  s −1 and the electrophoretic mobility of chlorophenol red was 1.2 × 10 −4 ± 7.7 × 10 −7  cm 2 V −1  s −1 . Basic separation protocols were optimized using colorimetric detection of chlorophenol red and indigo carmine dyes as representative molecules. Paper type, channel width, and applied potential were then used to optimize the separations. Addition of an injection port to the device improved resolution and reduced peak broadening. Finally, the separation of fluorescein isothiocyanate (FITC) and l -glutamic acid (Glu) labeled with FITC, was successfully carried out using the l-paper electrophoretic device. Imaging with a microscope was found to achieve reduced peak broadening and increased resolution relative to imaging with a mobile camera, due to elimination of background signal, achieving a 72 ± 4% conjugation of Glu and FITC. [ABSTRACT FROM AUTHOR]

Joint analysis of varied biomarkers in blood sample will provide more accurate results for the monitoring and management of Alzheimer's disease (AD). In addition to the known β-amyloid protein (Aβ) used as a reliable clinical marker for AD diagnosis, Fetuin B also demonstrates a strong correlation with AD progression. Especially, for medical diagnostics, on-site detection of multi-analyte is quite important and therefore, it is desirable to develop a rapid and portable, multiplex electrochemical assay for simultaneous detection of Aβ and Fetuin B, which has been seldomly reported before. To achieve this goal, a multiplex paper-based electrode was prepared via vacuum filtration, by which, single-walled carbon nanotubes (SWCNTs) and AuNPs were sequentially filtered through cellulose paper with a five-electrode pattern to form a conductive underlay and electrical connections. A nanocomposite of AuNPs-loaded dendritic mesoporous silica nanoparticles (dmSiO 2 -Au) was firstly synthesized and further deposited thionine (Thi) for signal amplification. An immunosensor was correspondingly fabricated, which involved a combination of multiplex electrodes and dmSiO 2 -Au-Thi nanocomposite to facilitate simultaneous monitoring of Aβo and Fetuin B. Additionally, ferrocene (F c) was applied onto a separate working electrode to perform a ratiometric electrochemistry for enhancing accuracy. The outcomes demonstrated high specificity, sensitivity, and stability, and no obvious cross-talking between three working electrodes. Application of this sensor resulted in a successful determination of Aβo and Fetuin B levels in serum and brain tissue of transgenic AD mice. Overall, the presented electrochemical immunosensors for performing multiplex diagnostics may facilitate to the exploration of more AD-related blood markers. • A multiplex paper-based electrode was prepared. • A sandwich-based immunosensor enabled simultaneous monitoring of Aβo and Fetuin B. • Ferrocene was applied onto electrode to construct a ratiometric electrochemistry. • Analysis of Aβo and Fetuin B in APP/PS1 transgenic AD mice was realized. [ABSTRACT FROM AUTHOR]

Multiple heteroatom doping is one of the effective strategies to tune the structure of carbon supports and enhance the catalytic performance of nanozymes. Herein, the carbon-based copper nanozyme with sulfur/nitrogen co-doping (S/Cu-NC) was synthesized by one-step pyrolysis of Cu-doped ZIF-8 with thiourea encapsulated (Th/Cu@ZIF-8). Benefiting from the synergy of binary heteroatoms and 3D porous structure, the obtained S/Cu-NC had more active sites and exhibited outstanding peroxidase-like activity. Subsequently, a dual-channel (colorimetric/fluorescent) detection method for melatonin was developed by selecting 3,3,5,5-tetramethylbenzidine (TMB) and thiamine as the substrates of S/Cu-NC, which was based on the free radical scavenging effect of melatonin. Furthermore, a simple and portable paper-based device was designed to realize the rapid detection of melatonin through color changes under ultraviolet light and daylight, and the limit of detection were 0.87 μM and 1.42 μM, respectively. This paper-based device was successfully applied to detect melatonin in two kinds of drug samples with satisfactory results. • The carbon-based copper nanozyme with S/N co-doping (S/Cu-NC) was synthesized by one-step pyrolysis. • S/Cu-NC exhibited enhanced peroxidase-like activity due to more activity sites brought by heteroatoms. • A portable paper-based device was constructed to realize the dual-channel rapid detection of melatonin. • The portable paper-based device was used to detection melatonin in two types of drug samples. [ABSTRACT FROM AUTHOR]

We report for the first time a one-step fabrication by lamination of inexpensive graphene paper (GP) based Ag/AgCl pseudo-reference (RE) and K+-selective coated-film electrodes forming the novelty of this work. Contrary to our previous work about laminated GP solid-contact electrodes, the electrode fabrication in this work does not require manual drop casting steps after the lamination, simplifying the fabrication and making it suitable for mass production. We also eliminated the need of the solid contact and simplified the electrode construction by placing the plasticized potassium-selective PVC membrane (ISM) directly on the GP functioning as combined electrode substrate and ion-to-electron transducer. Both Ag/AgCl and the ISMs were pre-deposited on rectangular GP sheets (10 ×100 mm2) before placing them inside laminating pouches and feeding them through an office laminator after which the electrodes were ready for use. Five batches of 32 pseudo-REs had a very good E 0 reproducibility of ± 2.8 mV. The K+-electrodes had a slope and detection limit of 57.4 ± 0.3 mV/pK (n = 4) and 6 × 10−7 M, and the E 0 reproducibility was in the best case only ± 1.2 mV matching the performance of non-laminated K+-electrodes. This work demonstrates that the ISMs are compatible with the lamination where the temperature can momentarily rise to ca. 130 °C. [Display omitted] • Hot lamination of planar and flexible graphene paper based pseudo-REs and ISEs. • One-step fabrication by lamination of low-cost electrodes that are suitable for mass production. • The Ag/AgCl pseudo-REs had a good batch-to-batch E 0 reproducibility of ± 2.8 (n = 32). • The K+-ionophore valinomycin does not degrade during hot lamination at ca. 130 °C. • Laminated K+-selective electrodes match the performance of non-laminated ones. [ABSTRACT FROM AUTHOR]

Paper spray ionization is a simple method to analyze samples by mass spectrometry (MS) without sample preparation. However, using paper substrates results in limited performance due to low lifetime, low reproducibility, severe analyte diffusion, and poor chromatography. To address these issues, a stereolithography 3D printed microfluidic paper-based column coupled to liquid chromatography-MS (µPC-LC-MS) was developed. The fabrication process created well-defined microchannels inside a single paper substrate in less than 1 s. The µPC-LC-MS significantly extended the lifetime of the substrate, up to 50 min per run with continuous gradient elution at a flow rate of 20 µL min-1 from regular LC pumps. A single µPC can be reused up to 5 cycles with an RSD of 9.5 % without signal reduction, overloading, or interference. Separation of three psychoactive substances/metabolites (methamphetamine, 7-aminonitrazepam, and morphine-3-glucuronide) was achieved with peak resolution from 0.50 to 1.21, high sensitivity (LOD between 0.5 and 1 ng mL-1) and accuracy (87.0–109.1 %), linearity from 5 to 500 ng mL-1 in both water and plasma, and coefficient of determination (R 2 ) from 0.993 to 1.000 using only 1 µL plasma. The µPC-LC-MS demonstrated robustness and sensitivity, making it a promising tool for bioanalysis based on paper-based microfluidics. [Display omitted] • Stereolithography 3D printed microfluidic paper-based columns extend PSI lifetime up to 50 min. • LC gradient was used for the first time in paper column chromatography. • A µPC showed 5-cycle reusability with 9.5 % RSD, no signal reduction, and no interference. • Plasma separation of 3 substances achieved with 0.50–1.21 peak resolution. • The method achieved a detection limit of 0.5–1 ng mL-1 using only 1 µL of plasma. [ABSTRACT FROM AUTHOR]

Handheld detection platform integrating ratiometric fluorescent N,P co-doped carbon dots (N,P-CDs) paper strip, smartphone, and 3D-printed accessory corroborates its efficacy for visual quantitative detection of Mn(VII) and GSH via a continuous fluorescence color shift. N,P-CDs were synthesized by hydrothermal treatment of 1,8-diaminonaphthalene, phosphoric acid, and formamide. Inspiringly, with increasing Mn(VII) concentrations, blue emission of N,P-CDs decreases gradually at 445 nm and a ratio rising orange band emerges at 600 nm under 340 nm excitation, which concurrently exhibits continuous fluorescence color variation of blue, purplish blue, purplish pink, pink, to orange. Subsequent addition of GSH renders orange fluorescence of N,P-CDs@Mn(VII) gradually quench but blue peak slightly enhance, accompanied by the fluorescence color successively returning from orange to blue. The RGB values of the resulting images were precisely defined by a color recognition application within the smartphone, and the R/B values could be employed for Mn(VII) and GSH quantification with linear ranges of 0 − 40 μM and 0 − 28 μM, respectively, as well as limits of detection of 24.49 nM and 21.41 nM, respectively. It is solicitously anticipated that our research will provide novel insight for the development of effective sensing protocol and the enlargement of practical application prospect. • Handheld detection integrates FL paper strip, smartphone and 3D-printed accessory. • Paper strip is stained by single ratiometric-FL CDs for Mn(VII) and GSH sensing. • High sensitivity is gotten due to well-resolved FL color shift of paper strip. [ABSTRACT FROM AUTHOR]

Herein, we report the clustering-triggered emission (CTE) behavior of ε-PL and its various applications. The CTE properties of ε-PL in solution were confirmed from the SEM analysis, DLS data, and the observation of the Tyndall effect. We explored these unique and unconventional photophysical characteristics of ε-PL for the selective detection of Cu2+ with a LOD of as low as 0.45 ppb (7.11 nM), which is much less than the safe limit set by the WHO for Cu2+ in drinking water (2 ppm). The quantum yield of ε-PL reduced from 0.24 to 0.008 upon Cu2+ addition, and the quenching was found to be dynamic in nature. Further, ε-PL was able to detect Cu2+ in real water samples (tap and lake water) as well as in living cells (MCF-7). For real-time applications, ε-PL-coated paper strips and silica gel were fabricated for rapid and convenient detection of Cu2+. The anti-counterfeiting application of ε-PL has also been demonstrated. These findings highlight an efficient method for the selective detection of Cu2+ by ε-PL, an unconventional fluorescent polymer without any chemical modifications, and its real-time applications in Cu2+ sensing and as an anti-counterfeit material. This potentiates its use in agriculture, waste management, medicine, and related fields. [Display omitted] • ε-Polylysine (ε-PL) exerts strong fluorescence in concentrated aqueous solution. • An as-prepared ε-PL solution acts as a fluorescence sensor for Cu2+ (LOD 0.45 ppb). • Cu2+ sensing in real water samples, ε-PL-coated paper strips for real time sensing. • Cellular imaging in MCF-7 cells with rapid detection of intracellular Cu2+. • ε-PL can be used as a medicine-anticounterfeit material. [ABSTRACT FROM AUTHOR]

Microfluidic technology facilitates high-throughput generation of time series data for biological and medical studies. Deep learning enables accurate, predictive analysis and proactive decision-making based on autonomous recognition of intricate pattern hidden in series. In this work, we first devised a paper-based microfluidic system for portable nucleic acid amplification test with economic energy consumption. Then, we employed Graph Neural Network (GNN), distinguished by its non-Euclidean data structure tailored for deep learning, with spatio-temporal attention mechanism to perform near-sensor predictive analysis of the on-chip reaction. Our findings demonstrated that the novel GNN model can provide accurate predictions of positive outcomes at the early stages of the reaction using less than one-third of the total reaction time. Then, the deep learning model trained by on-chip data was subsequently applied to more than 900 clinical plots. Generalization of the GNN model was successfully validated across different detection methods, diverse types of datasets and time series with variable length. Accuracy, sensitivity and specificity of the predictive approach were 96.5 %, 94.3 % and 99.0 % by utilizing the early half of reaction information. Finally, we compared the GNN model with various deep learning models. Despite differences in the prediction of negative samples among various models were minute, GNN obviously offered overall superior performance. This work ignites a cutting-edge application of deep learning in point-of-care and near-sensor tests. By harnessing the power of body area networks and edge/fog computing, our approach unlocks promising possibilities in diverse fields like healthcare and instrument science. [Display omitted] • Paper devices for economic on-chip amplification. • GNN analyzes data generated in paper devices and predicts reaction results quickly. • The deep learning model can work across platforms, methods & datasets. [ABSTRACT FROM AUTHOR]

This report describes for the first time the development of paper-based enzymatic reactors (PERs) for the detection of glucose (Glu) in artificial serum sample using a 3D printed batch injection analysis (BIA) cell coupled with electrochemical detection. The fabrication of the PERs involved firstly the oxidation of the paper surface with a sodium periodate solution. The oxidized paper was then perforated with a paper punch to create microdisks and activated with a solution containing N -hydroxysuccinimide (NHS) and N -(3-dimethylaminopropyl)- N ′-ethylcarbodiimide hydrochloride (EDC). Glucose oxidase (GOx) enzyme was then covalently immobilized on paper surface to promote the enzymatic assay for the detection of Glu in serum sample. After the addition of Glu on the PER surface placed inside a plastic syringe, the analyte penetrated through the paper surface under vertical flow promoting the enzymatic assay. The reaction product (H 2 O 2 ) was collected with an electronic micropipette in a microtube and analyzed in the 3D BIA cell coupled with screen-printed electrodes (SPEs). The overall preparation time and the cost estimated per PER were 2.5 h and $0.02, respectively. Likewise the PERs, the use of a 3D printer allowed the fabrication of a BIA cell within 4 h at cost of $5. The coupling of SPE with the 3D printed cell exhibited great analytical performance including repeatability and reproducibility lower than 2% as well as high sampling rate (30 injections h −1 ) under low injection volume (10 μL). The limit of detection (LD) and linear range achieved with the proposed approach was 0.11 mmol L −1 and 1–10 mmol L −1 , respectively. Lastly, the glucose concentration level was successfully determined using the proposed method and the values found were not statistically different from the data achieved by a reference method at confidence level of 95%. [ABSTRACT FROM AUTHOR]

• Blood glutathione is reagentlessly detected. • Paper-based strips allow to measure 5 μL of sample only. • Blood does not interfere with electrochemical measures. • Filter paper blocks gross impurities from blood. • Electrochemical strips allow for de-centralized tests. Paper-based devices are always more gaining a relevant position in the field of sensors. The continuous demand for affordable, simple, sustainable, and portable devices, is making paper as the ideal basis towards the realization of analytical tools for the easy self-testing. In this work, we demonstrate, for the first time, the development of a disposable paper-based printed electroanalytical strip for reliable, rapid, and high-throughput detection of glutathione in blood. The detection is based on the thiol-disulfide exchange reaction, which produces a detectable compound easily oxidizable at a Prussian Blue/carbon black nanocomposite involving a favorable low-interference overpotential. This nanocomposite is mixed within a carbon-based conductive ink and successively screen-printed onto a wax-patterned filter paper. The employment of paper provides a reagent-free device, as a consequence of the reagents pre-loading within the testing area. After the experimental conditions have been optimized, glutathione has been detected up to 10 mM, with a detection limit of 60 μM, and a sensitivity of (0.102 ± 0.005) μA/mM. This sensor showed satisfactory repeatability (relative standard deviation equal to 10%, for detection of glutathione 1 mM), especially by considering the hand-made manufacturing process. The "real-world" applicability of this strip has been evaluated by quantifying blood glutathione at physiological levels and by recovery studies achieving satisfactory values. [ABSTRACT FROM AUTHOR]

Developing simple assays to identify and discriminate quinolones are highly desired for food safety, which remain a great challenge due to the interferences from food matrices and the minor variation on the molecular structure of massive quinolones. We proposed a room-temperature phosphorescence (RTP) assay for the quantitative detection and discrimination of quinolones, aided by a confinement and heating strategy. Quinolones were loaded into the porous framework of paper, which provided confinement effects on the molecular motions of quinolones. The heating process further removed the solvents, eliminating their quenching effects on excitons. These synergistic effects improved the RTP intensity and emission lifetime by 1144-fold and from nanoseconds to seconds, respectively. Three types of quinolones were quantitatively detected and discriminated through pattern recognition methods. The proposed assay showed excellent detection performance in complicated meat samples, aided by the delayed signal collecting of RTP. The reported results provided a clue to modulate the RTP properties of organic molecules, showing great potential for application prospect in food safety analysis, environmental and healthy monitoring. • A room-temperature phosphorescence assay for detection and discrimination of quinolones was proposed. • The phosphorescence performances were promoted by a confinement and heating strategy. • The phosphorescence intensity and emission lifetime were promoted by 1144 folds and from nanoseconds to several seconds. • Quinolones and their mixtures were discriminated through pattern recognition methods. [ABSTRACT FROM AUTHOR]

• Microfluidic paper based sampling coupled with solid-state and solid-contact ISEs. • Development of inorganic salt modified paper substrates for heavy metals analysis. • Metal ions sorption by paper as limiting factor for paper based analytics of metals. Inorganic salt modified paper substrates were developed and utilized in microfluidic paper based sampling coupled with potentiometric ion sensors for the determination of heavy metals, such as Cd2+ and Pb2+. The application of paper based sampling without any paper substrate pre-treatment were characterized with super Nernstian response, while the paper substrates with inorganic salt pre-treatment were characterized with standard Nernstian response. The application of inorganic salt modified paper substrates was found advantageous when the cation of the salt in the conditioning solution was the same as the primary cations of the ion-selective electrodes (ISEs). A relatively high concentration of inorganic salts during pre-treatment of the paper substrates, namely Cd(NO 3) 2 or Pb(NO 3) 2 with subsequent measurement of cadmium(II) and lead(II), by Cd2+- and Pb2+-ISEs, respectively was needed to sustain Nernstian response of sensors. It was also found that paper substrates facilitate sorption of metal ions onto the paper substrates, with stronger binding strength given to Pb2+ over Cd2+. Moreover, the metal-paper interactions suggest concentration dependent sorption-desorption of metal ion, which can have direct limitations of the use of paper based analytics for the determination of low analyte concentration of heavy metals. [ABSTRACT FROM AUTHOR]

A series of aminoquinoline derivatives with different N -alkyl substituents were synthesized and used in the development of paper-based fluorescent sensors. In aqueous solutions, the quinoline ligands show strong green fluorescence selectively upon binding to Zn2+ that is clearly observed by naked eyes under blacklight illumination. The paper-based sensors were prepared by depositing the amidoquinoline derivatives in wax-printed channels on filter paper. Developing of Zn2+ samples, deposited below the ligand spots, with an aqueous buffer solution creates green fluorescent lines suitable for distance measurement. The ligands with a tertiary amino group showed better-defined fluorescent lines than those of ligands containing primary and secondary amino groups. The length of the fluorescent lines increases linearly with the amounts of Zn2+ in the range of 2.5–80 nmol that can be easily determined by naked-eye observation or an image processing software. The increase in hydrophobicity of the ligands results in a wider dynamic concentration range of the detection. The paper-based sensor can accurately and conveniently quantify Zn2+ in drinking water, dietary supplement, and fertilizer samples. • New series of fluorescent ligands having variable hydrophobicity were synthesized. • Paper-based sensors for of Zn2+ with distance-based quantification were developed. • Dynamic range of Zn2+ quantification increases with hydrophobicity of the ligands. • The sensor is handy for quantitative analysis of Zn in water and food supplements. [ABSTRACT FROM AUTHOR]

High levels of Cu (II) in the human body can cause kidney dysfunction, liver cirrhosis, and many neurological diseases, such as Wilson's disease (WD). Therefore, rapid and efficient detection of Cu (II) in urine is highly essential. First, by a simple multiple seeded growth method, the gold nanoclusters (Au NCs) embedded metal-organic framework (ZIF-8) is decorated on cellulose paper to generate a fluorescent Au NCs@ZIF-8 paper. Then the Au NCs@ZIF-8 paper is loaded on the fluidic cartridge integrated with the syringe for ultra-sensitive urine copper detection. The fluorescence paper is intercalated in a reusable fluidic cartridge and attached to a syringe, allowing the fluidic cartridge to flow a amount of samples through the paper. The interaction of Cu (II) with in situ growth of Au NCs@ZIF-8 on the paper induced fluorescence quenching, which fluorescence images can be recorded and analyzed by the portable smartphone-assisted device. Furthermore, a large amount of sample solution was flowed through the Au NCs@ZIF-8 paper, enabling more Cu (II) to react with the Au NCs@ZIF-8 paper on the novel paper-based analytical device (nPAD). Cu (II) detection can be completed by nPAD in 20 mins, and the limit of detection was as low as 9.2 nM. We show the value of the paper device for on-site detection of copper (II) and indicate that it has excellent potential for clinical applications and environmental monitoring. • A novel paper-based sensor was employed for ultrasensitive and accurate detection of Cu2+. • A fluorescent paper-based device is prepared by in-situ embedding the Au NCs@ZIF-8 on cellulose paper. • Au NCs@ZIF-8 paper equipment integrated with the fluidic cartridge dramatically boosts the sensitivity of detection. • The nPDA based on Au NCs@ZIF-8 paper equipment achieved a nanomole detection limit. • The nPDA was clinically validated with excellent accuracy for universal detection of Cu2+ in urine. [ABSTRACT FROM AUTHOR]

Microplastics (MPs) pollution has become a vital issue of worldwide concern owing to its associated hazards and the ubiquitous accumulation of MPs particles, which is correlated to their small sizes. Rapid identification and quantification of MPs represents an ongoing challenge in the field of environmental research. In this work, we prepared a fluorescence nanoprobe for identifying polyethylene (PE) MPs and developed a readily available method for the fast quantification of PE MPs in fluorescence mode. A kind of sulfur-doped carbon nanoparticles (S-CNPs) was prepared using nitrated pyrene and dithiosalicylic acid as precursors via a solvothermal process. S-CNPs showed no fluorescence emission in the solid state, whereas visible fluorescence was observed by labeling PE MPs. The surface environment-dependent emission of S-CNPs is an important factor in explaining the different emissions of different types of MPs, such as PE, polyvinyl chloride (PVC), and polystyrene (PS) for MPs identification. Notably, the distinction between PE and polypropylene (PP) was achieved using these S-CNPs according to their different staining efficiencies. Owing to its fast staining ability, a paper-based method for PE MPs quantification in water samples was developed using a simple vacuum-assisted suction filtration method and filter paper soaked with S-CNPs. Utilized as a readily available identification and quantification platform, these S-CNPs have great potential and could pave the way for MPs monitoring. • S-CNPs were prepared for rapid staining polyethylene microplastics. • Sulfur doping may have a positive effect on improving staining efficiency in these S-CNPs system. • A paper-based fluorescent sensor was constructed for the quantitative analysis in aqueous environmental samples. [ABSTRACT FROM AUTHOR]

On-site multi-enzymes detection and inhibitors screening are still challenging and particularly urgent. Here, dual-channel foldable microfluidic paper (μPAD)-based parallel enzymatic reaction systems were fabricated for simultaneous visual colorimetric detecting acetylcholinesterase (AChE) and α-glucosidase (α-Glu) together with screening inhibitors. μPAD composing of two layers with dual channels was designed and prepared facilely by a permanent marker. AChE and α-Glu catalyze pre-loaded substrates into products (thiocholine (TCh), ascorbic acid (AA)) on the 1st layer. Parallelly, oxidase-like MnO 2 nanosheets oxidize pre-dropped colorless 3,3′,5,5′-tetramethylbenzidine (TMB) to blue oxidized TMB (oxTMB) on the 2nd layer. After simple folding μPAD, TCh and AA can reduce oxTMB to TMB, resulting in color fading. Obviously, bioenzyme and nanozyme reactions under different pH can simultaneously occur on the μPAD. Furthermore, colorimetric results can be easily captured and on-site quantitatively analyzed by smartphone. As a result, a convenient, efficient, sensitive, and specific platform has been constructed for simultaneous detecting AChE and α-Glu in human serum samples (recoveries, 92.1–105.0%; relative standard deviations, < 3.6%), and screening inhibitors from synthesized compounds and natural products. The developed platform provides constructive insights for exploitation of visual detecting strategies for simultaneous sensing muti-targets for point-of-care testing of disease and development of drugs. [Display omitted] • Visual colorimetric detection of AChE and α-Glu and screening of inhibitors. • Dual-channel foldable μ PAD for on-site simultaneous visual detection. • Parallel enzymatic reaction strategy matches different working pH. • The proposed platform had facile, portable, and visual advantages in POCT. [ABSTRACT FROM AUTHOR]

A completely lab-made paper/graphene-based 3D pop-up device (3D-PP) for the analysis of carbaryl (CBR), a pesticide widely used in crop production, is proposed. The device is composed of a nitrocellulose sensor equipped with reduced graphene oxide (rGO) and a foldable 3D paper pop-up. The rationale of the device is based on 3D and 2D configurations to allow the whole analytical procedure. In the 3D arrangement sample pre-concentration and hydrolysis occur; after folding (2D), contact with the complementary nitrocellulose-based sensor is ensured. The sensor, constituted by nanostructured graphene film, allows to obtain the necessary electroanalytical performance. 3D-PP has been shaped and nanostructured using a CO 2 -laser plotter and finished using low-cost benchtop instruments, ensuring in-series manufacturing of the device modules. 3D-PP includes the main steps required for CBR determination, i.e. (i) pre-concentration/purification, (ii) hydrolysis, (iii) medium neutralization, and (iv) electrochemical detection. 3D-PP was challenged for CBR quantification in model solutions and different grain samples. The response linearity (1.5–33 μM) and LOD (0.4 μM) obtained ensures CBR determination at the European-law admitted maximum residue levels (MRL). As proof of applicability, to simulate contaminates samples, different grains (i.e. soft and durum wheat, kamut, and barley) were spiked, before extraction, with CBR at three concentration levels corresponding to 0.5x, 1x, and 1.5x MRL; in all cases, quantitative and reproducible recoveries were obtained (93–109%; RSD ≤ 6%, n = 3). 3D-PP is produced using cellulosic components and solvent-free approaches, includes all CBR analysis steps, and returns reliable results in 15 min, resulting portable and usable with a smartphone [Display omitted] • A paper/graphene-based device for integrated carbaryl (CBR) analysis is proposed. • CO 2 -laser was used to shape and nanostructure the paper-based platform. • Complete CBR analysis is strategically enclosed in a 3D foldable paper pop-up (3D-PP). • 3D-PP design and sensing ability allow CBR residues analysis at EU-law limits. • 3D-PP analysis ability was proven in soft and durum wheat, kamut, and barley. [ABSTRACT FROM AUTHOR]

Knowing the level of sugars in food and beverages is essential because they are related to diseases such as diabetes, and obesity, among others. In this regard, an approach has been designed, characterized, and applied to develop the first all-in-one paper-based microfluidic analytical device for the quantification of sugars in milk samples. In particular, the powerful combination of the paper-based platform, the facile manufacturing, and the on-demand customization, allowed to obtain a stand-alone platform that was capable to store all the reagents necessary for the assay, to treating the sample by removing major interferences due to lipids and proteins, and to visualize the results in minutes. A wax-patterned chromatographic paper was finely designed to provide a reagent-free platform for the use of non-specialists applied towards the analysis of sugars' content (lactose as the main sugar). Sugars were electrochemically quantified down to 0.16 g L−1 with a repeatability of 5%. To strengthen the efficacy of the novel platform, the electrochemical paper-based analytical device has been applied to commercial milk, including skimmed, semi-skimmed, whole, and lactose-free, confirming satisfactory performance with analytical reliability. This paper-based architecture opens novel avenues for portable (bio)sensing of other relevant species, not only in the agri-food field. [Display omitted] • Fully-printed and paper-based electrochemical device for application to sugars in milk. • The structure of chromatographic paper avoids tasks for final users. • The separation of the protein fraction is autonomously performed on the paper-based strip. • High-porous surface of chromatographic paper allows to reduce the time of analysis/reaction. • Everything has been obtained with the use of affordable and in-house procedures. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Molecularly imprinted paper-based sensor was prepared via polymerization-free method. • The synthesis was carried out by dissolving nylon-6 in formic acid. • The use of filter paper increases the versatility and manageability of the material. • Sensor was evaluated by extracting aqueous solutions of quinine and a soda drink. • Molecularly imprinted paper-based analytical device can be reused at least six times. Abstract In the last years, the imprinting technology has raised attention and different polymers with artificial recognition sites towards a target molecule have been developed. In this article, a polymerization-free method ―which only requires the dissolution of nylon-6 polymer and its subsequent incubation with the template molecule― has been employed for the preparation of a molecularly imprinted polymer directly immobilized on filter paper, thus increasing the versatility and manageability of the new material. The molecularly imprinted paper-based analytical device (MIP PAD) has been coupled to a fluorimeter via a custom-built platform, which enables direct measurement of the fluorescence at the surface of the MIP PAD. Extraction efficiency of the MIP PAD was evaluated using quinine as model analyte, measuring the fluorescence directly at the MIP PAD surface after incubation on aqueous standards of quinine and soda drink, showing that the performance of the imprinted material was superior to that of the non-imprinted polymer. In addition, the selectivity of the MIP PAD versus analogous organic fluorescent molecules has been further evaluated using norfloxacin, observing that the molecular imprinting results in selective extraction of quinine. The performance of the method has been evaluated for quantitative analysis, achieving limits of detection (LOD) and quantification (LOQ) for aqueous standards of 0.37 and 1.24 mg L−1, respectively, while in the case of spiked soda drink the LOD and LOQ were 0.63 and 2.11 mg L−1, respectively. The reproducibility of the measurements was also evaluated, observing values within range 2.30 and 9.07% measured as relative standard deviation. [ABSTRACT FROM AUTHOR]

Numerous fabrication methods have been reported for microfluidic paper-based analytical devices (μPADs) using barrier materials ranging from photoresist to wax. While these methods have been used with wide success, consistently producing small, high-resolution features using materials and methods that are compatible with solvents and surfactants remains a challenge. Two new methods are presented here for generating μPADs with well-defined, high-resolution structures compatible with solvents and surfactant-containing solutions by partially or fully fusing paper with Parafilm ® followed by cutting with a CO 2 laser cutter. Partial fusion leads to laminated paper ( l -paper) while the complete fusion results in infused paper ( i -paper). Patterned structures in l -paper were fabricated by selective removal of the paper but not the underlying Parafilm ® using a benchtop CO 2 laser. Under optimized conditions, a gap as small as 137 ± 22 μm could be generated. Using this approach, a miniaturized paper 384-zone plate, consisting of circular detection elements with a diameter of 1.86 mm, was fabricated in 64 × 43 mm 2 area. Furthermore, these ablation-patterned substrates were confirmed to be compatible with surfactant solutions and common organic solvents (methanol, acetonitrile and dimethylformamide), which has been achieved by very few μPAD patterning techniques. Patterns in i -paper were created by completely cutting out zones of the i -paper and then fixing pre-cut paper into these openings similar to the strategy of fitting a jigsaw piece into a puzzle. Upon heating, unmodified paper was readily sealed into these openings due to partial reflow of the paraffin into the paper. This unique and simple bonding method was illustrated by two types of 3D μPADs, a push-on valve and a time-gated flow distributor, without adding adhesive layers. The free-standing jigsaw-patterned sheets showed good structural stability and solution compatibility, which provided a facile alternative method for fabricating complicated μPADs. [ABSTRACT FROM AUTHOR]

Paper-based ion-selective optodes (ISOs) allow for low-cost ion measurements using widely accessible optical detectors such as smartphones, representing an attractive analytical platform for medical testing and environmental monitoring. Previously reported paper-based ISOs rely on plasticized PVC membranes or PVC/plasticizer-free adsorption layers containing hydrophobic sensing chemicals. In this paper, we studied a new format of paper-based ISOs, in which a plasticizer phase containing sensing chemicals is deposited onto cellulose paper without using a hydrophobic polymer like PVC. Compared to ISOs without plasticizers and polymers, the plasticizer-based ISOs show much higher pH sensitivity when using chromoionophore I and tetrakis[3,5-bis(trifluoromethyl)phenyl]borate as the sensing chemicals. When the sensing layer further contains a solid ionophore with high molecular rigidity, the plasticizer-based ISOs for cations also exhibit enhanced sensitivity than the plasticizer-free ISOs. However, when the ionophore is a liquid at room temperature or has a long alkyl chain, the plasticizer-based and plasticizer-free ISOs have comparable responses because the ionophore behaves as a pseudo-plasticizer. Compared to ISOs with both plasticizers and polymers, the elimination of hydrophobic polymers like PVC makes inkjet printing more efficient and preserves the capillary action of the porous paper. By using the newly launched Samba cartridge with smaller nozzles, the plasticizer-based and polymer-free optodes for sodium, potassium, and calcium ions are prepared by inkjet printing for the first time. In an example application, the inkjet-printed plasticizer-based and polymer-free ISOs are used for colorimetric measurements of urine calcium. • Plasticizer-based and polymer-free ion-selective optodes are fabricated on cellulose paper. • The use of plasticizers enhances the optode performance compared to plasticizer-free optodes. • Inkjet printing of the plasticizer-based optode ink is realized using the newly launched Samba cartridge. • The inkjet-printed optodes are used for colorimetric calcium measurements in urine. [ABSTRACT FROM AUTHOR]

• Br doped PEDOT modified carbon paper electrode is constructed through situ thermal polymerization. • The photocurrent of Br doped PEDOT was enhanced due to the doping of Br. • Br doped PEDOT was adopted as photoactive material the first time and was applied in PEC. • The as-prepared electrode can be volume production with good reproducibility. • The constructed Hg2+ PEC sensor exhibited speedy response, outstanding stability, excellent selectivity, wide linear range. Mercury (Hg) is a kind of the most common heavy metals with high toxicity in nature, existing in water, soil, and even food. Hence, it is of great importance to develop a simple, effective way to detect Hg2+. Flexible sensing has attracted extensive attention in recent years, which can be flexibly applied in various detection environments. Poly(3,4-ethylenedioxythiophene) (PEDOT) with conjugation structure which can accelerate the transfer of electrons and inhibit the recombination of carriers is favorable to the photoelectrochemical (PEC) process. Here, Br doped PEDOT modified carbon paper with narrower bandgap was firstly fabricated through situ thermal polymerization which exhibited high photocurrent intensity under visible-light irradiation. The success synthesis of PEDOT was confirmed by SEM, XPS, FT-IR and Raman spectrum. Meanwhile, the as-prepared electrode can be mass produced with good reproducibility. Based on excellent performance of as-prepared electrode of Br doped PEDOT/carbon paper, we constructed a PEC sensing platform for Hg2+ detection with the detection limit of 0.3 nM and linear range from 1 nM to 450 nM. In addition, the PEC sensor exhibited speedy response, outstanding stability, excellent selectivity, wide linear range, and was used for determination of Hg2+ in river water samples with recover range of 97.7–104.5 % and RSD of 2.8–4.7 %. [ABSTRACT FROM AUTHOR]

We developed an electrochemical paper-based device (ePAD) for the online separation and simultaneous determination of structurally similar carbofuran (CBF) and carbaryl (CBR). Our device combined paper chromatography and an electrochemical sensor as a single system for increasing the selectivity to simultaneous detection of the two pesticides. During the simultaneous detection of CBF and CBR, the separation of the two carbamate compounds depends on the differences between the movements of the substances on the chromatographic paper in the moving phase flow. The isolated pesticides were electrochemically measured using an amperometric method. Under optimal conditions, which include the effect of the mobile phase, separation channel, and the applied potential, the proposed device provides a linear range for the simultaneous determination of CBF and CBR from 0.1 to 2.0 and 0.5–7.5 mg L−1, with the limits of detection at 0.06 and 0.40 mg L−1, respectively. Furthermore, we successfully used the developed device to determine CBF and CBR in water, cucumber, and cabbage samples. The obtained results correspond to results obtained from a standard method. This developed ePAD is low-cost and uses a low sample volume (2 µL). Moreover, it is disposable, portable, and a promising tool for the on-site quantification of pesticides in actual samples. • Paper chromatography integrated with electrochemical detection (ePAD) is highlighted. • A separation-based ePAD was first developed for detection of CBF and CBR pesticides. • Online separation and simultaneous detection of structurally similar compound were achieved. • The ePAD provides highly selective and sensitive detection of CBF and CBR. • This sensor was successfully applied to determine CBF and CBR in real samples. [ABSTRACT FROM AUTHOR]

• This PDA-paper chips can detect pH1N1 virus directly with the naked-eye through color change. • The detection sensitivity of PDA-paper chips is improved by disturbing the PDA matrix with temperature increase. • PDA-paper chip as a colorimetric biosensor is suitable to use as point-of-care testing (POCT) device. We have developed polydiacetylene (PDA)-based colorimetric biosensor for point-of-care testing (POCT) to detect high infectious pH1N1 virus among influenza A virus with the naked eye by color change. For this purpose, we first prepared PDA-PVDF membrane by immobilizing PDA onto the PVDF membrane through photo-polymerization, and then conjugated an antibody specifically binding to the influenza A virus into this membrane to form PDA-paper chips. This PDA-paper chips exhibited unique chromatic properties involving a color change from blue to red under various external conditions (temperature and pHs). Especially, we showed the color change of this paper chip in the presence of pH1N1 virus, confirming its potential as a POCT device. Furthermore, we have developed POCT systems based on PDA-paper chips by developing program, which is possible to visually detect viruses using only PDA-paper chips at a high concentration and detect and analyze them at low concentrations using both paper chips and program (App.). Further, this program will be updated to enable quantitative analysis of the virus. [ABSTRACT FROM AUTHOR]

Highlights • The microfluidic paper based analytical devices (μPADs) with no need of hydrophobic backside can be fabricated by microembossing within 1 min. • The protruded structure is obtained after embossing, which becomes the channel after heating the wax on the backside of the filter paper. • The μPADs with minimum 2 mm channel width were made by Whatman No. 3 paper at pressure larger than 50 kg/cm2, and wax heating time ranging from 15 to 45 s. • The glucose detection was performed and a linear relationship was obtained between 5–50 mM glucose concentrations. Abstract In this study, fabrication of microfluidic paper based analytical devices (μPADs) by microembossing was proposed. Different from the embossing methods described in the literature, the filter paper was embossed such that a protruded structure was formed, which subsequently became the channel after heating the wax at the backside of the filter paper. It was found that, when using the Whatman No. 3 filter paper, the embossing pressure needed to be larger than 50 kg/cm2 in conjunction with using a minimal 2-mm wide channel, and the wax heating time ranged from 15 to 45 s in order to obtain a reliable μPAD with repetitive and consistent results. In addition, there was no need of a hydrophobic material as the backside support. The glucose detection was demonstrated using the μPADs as fabricated and a linear relationship was obtained between 5 and 50 mM glucose concentrations. With the proposed method, the processing time of fabricating μPADs can be reduced within approximately 1 min. [ABSTRACT FROM AUTHOR]

This study presents a simple, fast, and sensitive method for multiplexing heavy metal detection. Using a chemically patterned microfluidic paper-based analytical device (C-μPAD), silane compounds terminating in amine (NH 2 ), carboxyl (COOH), and thiol (SH) were immobilized on a patterned chromatography paper via condensation reactions. Three chromogenic reagents that react distinctly with Ni(II), Cr(VI), and Hg(II) were then covalently coupled to these functional groups. These functionalized C-μPADs were then evaluated for heavy metals ions detection with spiked water samples. Using a single-plex platform, we achieved detection limits as low as 0.24 ppm for Ni(II), 0.18 ppm for Cr(VI) and 0.19 ppm for Hg(II). The detection limits for this single-plex platform were twice as good as those obtained in previous studies using colorimetric analysis due to the formation of homogeneous metal complexes from immobilized chromogenic reagents. Furthermore, by minimizing cross-reaction with chelating agents and maximizing reaction uniformity, multiplex heavy metal ion detection was successfully demonstrated for lake-water samples spiked with various concentrations of heavy metal ions with high precision. This functionalized C-μPAD provides a highly portable and rapid on-site monitoring platform for multiple heavy metal ions detection with extremely high repeatability, which is useful for resource-limited areas and developing countries. [ABSTRACT FROM AUTHOR]

We report an innovative sensor for the determination of low levels of total cholesterol (TC) in saliva. The sensor consists of an enzyme-loaded nitrocellulose (NC) paper and an impedimetric sensor based on hybrid material derived from Pt black/PEDOT:PSS (BPt/PEDOT) and Pt black/Nafion (BPt/Nafion) composite. The enzyme-loaded NC paper combined impedimetric sensor with the BPt/Nafion composite was able to detect TC values in the range of 5–4000 ng/ml with a normalized sensitivity (impedance change) of 7.5%/decade at 1 kHz and 0.99 linear correlation. In order to detect cholesterol in saliva reliably, the detection limit should be lower than the clinical level in saliva (5–46 μg/ml). The fabricated sensor had a detection limit that was sufficiently low and it had a wide detection range. In addition, the impedimetric sensor with BPt/Nafion composite exhibited more reproducible and cholesterol-selective normalized impedance changes than the sensor with the BPt, BPt/PEDOT electrode. In the human serum and saliva test, the impedance change from diluted serum and saliva concentration was compared. The impedimetric sensor exhibited relatively well matched correlation between diluted serum and standard TC. And TC concentration in saliva was at least 10 −3 less than the concentration in the serum. [ABSTRACT FROM AUTHOR]

The early detection of prostate cancer (CaP), one of the most common cancers in males, improves treatment efficacy. However, current methods to detect CaP are limited by specificity and sensitivity or require an invasive and unpleasant procedure. Therefore, there is a need for a novel, fast, and noninvasive CaP detection method. This proof-of-concept study aimed to diagnose CaP from urine samples by detecting the UV-induced fluorescent clusters formed in situ that reflect a urine composition specific to CaP patients using fluorescence spectroscopy. The UV-induced clusters formed upon irradiation by UV light with a wavelength of 254 nm were detected at excitation and emission wavelengths of 400 nm and 460 nm. Fifteen patients with CaP were correctly distinguished from 5 controls. The different stages of CaP could be further determined using molecular imprinting technology. Additionally, a paper-based analytical device was developed that enabled the correct identification of stage I cancer patients by fluorescent spectroscopy detection and the naked eye. In conclusion, this novel, easy-to-operate, point-of-care assay can enable early diagnosis of CaP with high accuracy and judgement of the disease stage. The simplicity, as well as versatility of the proposed method, will enable its application also to other diseases and disorders. • Easy-to-operate, point-of-care assay for diagnosis of prostate cancer from urine samples. • Prostate cancer detection with high accuracy and judgement of the disease stage. • UV-Induced fingerprint spectroscopy was combined with molecularly imprinted polymers. • Simple diagnostic by a paper-based analytical device was enabled. [ABSTRACT FROM AUTHOR]

Programmed death ligand 1 (PD-L1) of tumor-derived extracellular vesicles (T-EVs) is an important biomarker to predict immunotherapy response. The traditional bioassays of T-EVs PD-L1 are limited by the detection specificity because of the distribution of the signals by PD-L1 from nontumor-derived EVs, which leads to unsatisfactory predictive accuracy. In this work, we developed a simple and ultrasensitive method for the quantification of T-EVs PD-L1 by using the lipid bilayer magnetic interface as the isolation and enrichment carrier along with hybridization chain reaction (HCR) for signal amplification in a paper-based device. First, magnetic beads were covered by liposome bilayers and then anchored with the cholesterol modified epithelial cell adhesion molecule (EpCAM) aptamer to construct a fluid multivalent magnetic interface and realize the high-performance isolation of T-EVs. Moreover, the biosensor relied on the PD-L1 aptamer to initiate the HCR of EVs. Benefiting from the high isolation ability of the lipid bilayer magnetic interface and the high signal amplification ability of HCR, the dual-aptamer-based biosensor is capable of highly sensitive detection of T-EVs with a detection limit as low as 5.0 EVs·µL−1 in a paper-based device. Overall, the paper-based lipid bilayer magnetic interface biosensor not only can serve as an alternative tool for predicting the immunotherapy response but also displays great potential in point-of-care disease diagnosis. • A paper-based lipid bilayer magnetic affinity interface for detection of T-EVs PD-L1. • The lipid bilayer magnetic interface realizes the high-performance isolation of the T-EVs. • PD-L1 aptamer was used to initiate the HCR of EVs to amplify the signal. • The dual-aptamer-based biosensor realizes ultrasensitive detection of T-EVs. • The biosensor can detect T-EVs in cancer patient samples without purification. [ABSTRACT FROM AUTHOR]

Patients under medical emergency may require urgent blood transfusion as life-saving measures, including the situations demanding for operative intervention. However, while traditional blood grouping is an established practice before such procedures are administered, possibilities of having rare blood groups (like Bombay factor/hh group) remain to be undetected. Unfortunately, such rare blood groups may trigger adverse haemolytic reactions post the intervention, disrupting the success of blood transfusion, organ transplantation, and in vitro fertilization process-flow, among others. Currently, the established option for isolating such patients is to carry out elaborate DNA sequencing, albeit only after they start presenting life-threatening symptoms that may be difficult to arrest, whereas any approach of detecting such patients a-priori remains to be introduced. Here, we report the development of an affordable three-fold test kit that integrates the isolation and purification of the DNA sample from few drops of blood (∼70 microliter), perform its isothermal amplification and arrive at a rapid readout that is agnostic to any colorimetric inference. We demonstrate the efficacy of this methodology in a portable, user-friendly and inexpensive sample-to-answer framework that is amenable for execution at the patient's site without demanding laboratory-centric procedures, within about 30 min of sample dispensing. The favourable sensitivity and specificity of the technology presents it as a value proposition for routine screening prior to administering blood-group sensitive clinical procedures – a paradigm that has thus far not been reported. • First point-of-care test for rare blood group. • Genomic DNA isolation, isothermal amplification and detection -in-one sample-to-answer format. • Detecting a deletion mutation of a test gene with high sensitivity and specificity. • Small volume (∼70 microleter) of human blood samplesneeded for the 30-minute test. • Executable outside controlled laboratory settings with high efficacy. [ABSTRACT FROM AUTHOR]

Many microfluidic "lab on paper" devices have been demonstrated for point-of-use applications, but scalable fabrication methods are necessary for these devices to make it past the proof-of-concept stage and become viable commercial products. Commercially available wax printers such as the Xerox ColorQube presented a near-ideal compromise between cost, ease of prototyping, and throughput, but in 2016, these printers were discontinued, and now, alternative methods are needed. In this review, we survey current paper analytical device (PAD) fabrication methods through the lens of scalability, focusing on the tradeoffs between resolution, ease of prototyping, cost, and throughput. Categories discussed include handmade, semi-automated, batch, laboratory-based, printer-based, and roll-to-roll fabrication methods. Hand-, batch-, semi-automated, and laboratory-based fabrication methods suffer from low throughput and high hands-on labor requirements. Roll-to-roll methods are high throughput but costly, while printer-based methods offer a compromise between cost and throughput. By highlighting the comparative merits of existing methods, we hope to offer insight into what makes a method "scalable" or "manufacturable." • We compare throughput, cost, ease of prototyping, and resolution for 25 classes of paper device fabrication methods. • Most fabrication methods are not suitable for medium- or large-scale manufacture. • Printer-based and roll-to-roll methods offer the most direct translation from lab to factory scale. [ABSTRACT FROM AUTHOR]

• The MoS 2 -AuNPs probe showed uniquely inherited structure and excellent electrochemical characteristic. • The carbon paper functionalized with MoS 2 -AuNPs demonstrated the outstanding detection performance of p53 gene. • The biosensor exhibits a relatively lower detection limit of 68 fM for p53 gene detection. • The planned biosensor could discriminate well between the mutated and wild type p53 gene extracted from tumor cells. p53 gene is one of the most important anticancer genes and has been recognized as a typical biomarker for the early diagnosis, classification, and prognosis evaluation of cancers. In this work, a novel biosensing strategy integrating MoS 2 -AuNPs modified carbon paper (CP) conductive substrate and enzyme signal amplification technique was developed for p53 gene detection. We constructed an immobilized DNA S1 probe and a biotinylated DNA S3 probe, which could induce the formation of an S1-p53-S3 DNA sandwich complex in the presence of target sequence p53. After conjugating avidin-HRP via biotin-avidin reaction, 3,3',5,5'-tetramethylbenzidine would be catalyzed for signal amplification in the presence of H 2 O 2 so that the induced electrochemical response would change with proportional to the abundance of p53 gene. The proposed biosensor exhibited two linearities in the range of 1.0 × 10−15 ∼ 1.0 × 10-12 M and 1.0 × 10-12 ∼ 1.0 × 10-6 M, and the limit of detection (LOD) was 68 fM. No significant interferences were observed during detecting real serum samples. Moreover, it is worth pointing out that the biosensor together with its disposable, low-cost, and stable features can discriminate well between the mutated and wild type p53 gene extracted from tumor cells (wtTP53 in MCF-7 and mutated in SK-BR-3), demonstrating a promising applicability for clinical test. [ABSTRACT FROM AUTHOR]

Palladium in the form of G-Pd nanocomposite possesses multiple enzyme mimicking activity. It catalyzes the oxidation of dopamine, glutamate, H 2 O 2 and NADH through dopamine oxidase, glutamate oxidase, peroxidase and NADH oxidoreductase biomimetic activity. Kinetic studies were performed to calculate the catalytic parameters of G-Pd nanocomposite towards the substrates for a potential heterogeneous catalyst. Among them, glutamate oxidase activity was coupled with peroxidase activity of G-Pd for the detection of glutamate, in the form of a paper based sensor. Analytical performance of G-Pd nanocomposite catalyzed glutamate detection was characterized, and found to be linear in the range 0–400 μM and 400–8000 μM with limit of detection and quantification of 49.4 μM and 117.9 μM respectively. Results from the present study provides substantial progress in the practical application of nanomaterials as heterogeneous catalysts with multi enzyme mimicking property. G-Pd nanocomposite overcomes the complexity of enzyme based biosensors due to less number of reagents, better stability due to the absence of enzymes with mild storage conditions. Multi-mimetic catalytic activity of Pd will find applications in the field of analytical chemistry, biosensors, energy, environment and food safety. [ABSTRACT FROM AUTHOR]

We present a tilted fiber Bragg grating (TFBG) sensor coated with crystal violet/perfluorinated sulfonic acid (CV/Nafion) composite film for relative humidity (RH) monitoring. The composite film demonstrates the characteristics of an optical "humidity test paper" by exhibiting a color transition from yellow to green within a RH range of 10 % to 80 %. This color variation indicates its potential to effectively monitor RH levels in diverse environments. To achieve a quantitative RH sensing, we coat CV/Nafion composite film on an etched TFBG (ETFBG), where surrounding RH changes can be measured from spectral responses of ETFBG transmission. In experiments, the proposed the CV/Nafion-coated ETFBG sensor exhibits RH sensitivities of 0.068 dB/%RH and 3 pm/%RH for intensity change and wavelength shift measurements, respectively, within a relative humidity (RH) range of 10 % to 80 %. Additionally, based on intensity measurement, short response and recovery times of ∼4.4 and ∼4.6 s are estimated from a continuous RH monitoring. • The proposed sensor's color will change from yellow to green with the increasing of the RH. • The proposed sensor could be used for RH detection of liquids, gases, and solids. • High RH detection sensitivity of 0.068 dB/% RH was obtained. • The response and recovery times are 4.4 s and 4.6 s respectively. [ABSTRACT FROM AUTHOR]

Arsenic contamination is widespread in water bodies and poses a significant risk to human health, thus developing a rapid and inexpensive in situ method for the detection of arsenic is urgently needed. In this study, a chitosan-catechol carbon paper electrode was fabricated by electrodeposition of chitosan on a conductive carbon paper and subsequential electro-oxidative grafting of catechol. This chitosan-catechol modified electrode demonstrated good performance in detecting trace amounts of arsenic, which is mainly due to the significantly amplification of oxidation signals generated by ferrocene (Fc) on chitosan-catechol hydrogel. The interaction of As(III) with quinone and semiquinone radicals results in the decrease of electronic transmission nodes. The modified electrode exhibited a good detection capability of low concentration As(III) with a detection limit 0.82 ppb by differential pulse voltammetry (DPV). In addition, the chitosan-catechol modified sensor has the merits of high reproducibility, durability and strong resistance to ionic interference. Further successful detection of As(III) in actual rice and soil samples suggests its good potential in the field of in situ detection. [Display omitted] • Modified paper sensor was constructed by catechol grafting without gold modification. • The redox of catechol allows a significant amplification of oxdation signals. • Modified paper sensor achieves a LOD of 0.82 ppb for As(III) detection. • Actual rice and soil samples can be analyzed by the modified paper sensors. [ABSTRACT FROM AUTHOR]

Excellent detection capability, a simple assay procedure, and easy device acquisition are three key factors to analyze biomarkers for disease diagnosis using a point-of-care device in resource-limited settings or in emergency situations. However, constructing a platform with the simultaneous presence of these factors to sense multiple biomarkers remains a challenge. In the spirit of "frugal science", a simple method is developed by combining a low-cost portable paper centrifuge with surface-enhanced Raman scattering (SERS) immunoassay for sample pretreatment and multiple-cytokine (IL-6, IL-1, and TNF-α) detection. The paper centrifuge can achieve rapid blood separation as a commercial centrifuge and also concentrate sandwich immune composites to generate abundant hot spots, thus enhancing the SERS signal. By analyzing three prospective cytokines (IL-6, IL-1, and TNF-α) closely related to tumors, the combined paper centrifugation–SERS immunoassay method realizes sensitive assays with detection limits down to 0.86, 0.42 and 0.22 pg/mL. Meanwhile, the proposed approach possesses capabilities of specific recognition and accurate quantitative detection for three cytokines in serum. Hence, the constructed multifunctional SERS platform is expected to be applied in the development of decentralized and battery-free diagnostic devices in facility-limited areas and field settings. [Display omitted] • A combined paper centrifugation–SERS immunoassay method is developed. • Paper centrifuge can achieve rapid blood separation as a commercial centrifuge. • Sensitive, quantitative, and specific detection for three cytokines are realized. [ABSTRACT FROM AUTHOR]