Search

Fibrinogen is a blood protein that is essential for clotting. It is converted into the polymer fibrin by the blood enzymes thrombin and factor XIIIa. Fibrinogen is one of the first proteins to be depleted in heavily bleeding patients. Patients with early hypofibrinogenemia need urgent fibrinogen replenishment to prevent the onset of haemorrhage and death. However, currently there is no rapid, sensitive, cheap and easy-to-use fibrinogen assay that can detect fibrinogen concentrations. In this study, we have developed a new paper-based diagnostic to quantify the fibrinogen concentration in blood at room temperature. This diagnostic is a 2-step process: first, plasma is added onto thrombin-treated paper strips where fibrinogen is converted to fibrin; then the strips are placed into an aqueous dye bath where elution occurs. The test operates by measuring the change in hydrophobicity, which increases with fibrinogen concentration under otherwise constant conditions. The diagnostic can precisely measure fibrinogen concentration within the range of 0-2 g L-1, which is ideal for the clinical diagnosis of hypofibrinogenemia. Furthermore, testing needs only 12 μL of plasma, 60 mU of thrombin and 7.5 minutes of testing. This diagnostic has the potential to revolutionise point of care testing and save many lives.

The combination of smartphone technology and colorimetric paper-based microfluidics can enable simple, inexpensive diagnostics. However, imaging colorimetric diagnostic results via smartphones currently requires accessories to mitigate the influence of variability in surrounding lighting conditions. Here, we present an accessory-free smartphone-based colorimetric imaging method that enlists the built-in LED light source to dominate ambient lighting in combination with background and colour rescaling. This simple approach enables quantitative measurements from paper-based tests by compensating for different environmental lighting conditions and is universally applicable with respect to phone models and manufacturers. We demonstrate the method with three dominant phone makes and models in a cell counting application with a paper-based yeast detection device. The detection results are in good agreement with cell counting using automated cell counters. Eliminating the need for make/model specific accessories, this approach helps realize the potential for low-cost, broadly applicable paper-based diagnostics.

Cellulose paper derived from plants is used for daily writing and recording and has historically played an important role in promoting cultural dissemination and inheritance. However, it has attracted increasing attention in recent years, serving as a flexible platform or substrate for environment and energy applications, which is attributed to its many inherent advantages such as biocompatibility, biodegradability, sustainability, low cost, and great capability to be modified. With the development of various industries, especially the flexible electronics industry, the demand for two-dimensional (2D) paper-like materials have increased. Several types of inorganic paper are manufactured and have been widely used in many fields. Among them, hydroxyapatite (HAP)-based and carbon-based inorganic paper exhibit unique advantages and have been well applied in certain fields. In addition, there are many composite papers assembled by several raw materials (cellulose fibers, HAP, and carbon), exhibiting excellent characteristics. Cellulose paper is no longer limited to traditional writing applications and has great potential to be used in many aspects, achieving a stunning change in its role. The emergence of inorganic paper and hybrid paper has further demonstrated the application prospects of paper-like two-dimensional materials. Herein, initially, we present the characteristics of three types of paper and composite paper, and then summarize their typical applications in the environment and energy fields. [ABSTRACT FROM AUTHOR]

Solar-driven interfacial steam generation (SISG) has received increasing attention due to its continuous clean water generation under sunlight irradiation with high photothermal conversion efficiency. However, the inevitable waste of solar thermal energy and the poor adaptability of the photothermal material severely restrict its practical application. Herein, we report for the first time the fabrication of flexible and free-standing alkaline-earth metal ios-mediated graphene oxide nanoribbon paper (GONRs paper) by utilizing the ring-opening and cross-linking reactions of GONRs with M (Mg2+, Ca2+, Sr2+ or Ba2+). Owing to the unique structure, the as-created GONRs-M paper embraces all the desirable capabilities, including light absorption, thermal conversion, and wetting ability, and enables continuous clean water production from seawater and simulated wastewater with nearly 91.5% photothermal conversion efficiency under one solar intensity irradiation (1 kW m−2). In addition, complementary heat loss-induced thermoelectricity is harvested alongside SISG, ensuring simultaneous desalination and electricity production with high efficiency. This facile strategy opens an avenue for developing GONR paper-based durable steam generators, not merely for sustainable clean water production, but also for harvesting low-grade waste energy. [ABSTRACT FROM AUTHOR]

Simultaneous detection of multiple amino acids (AAs) instead of individual AAs is inherently worthwhile for improving diagnostic accuracy in clinical applications. Here, a facile and reliable colorimetric microfluidic paper-based analytical device (μPAD) using carbon dots doped with transition metals (Cr3+, Mn2+, Fe3+, Co2+, Ni2+, Cu2+, and Zn2+) has been provided to detect and discriminate 20 natural amino acids. To make the colourless metal-doped carbon dots suitable for colorimetric assays, they were mixed with ninhydrin to form a charge transfer complex. This optical tongue system, which was constructed by dropping mixtures of ninhydrin with a series of metal-doped carbon dots on a paper substrate in an array format, represented obvious but different colorimetric signatures for every examined amino acid. Since bovine serum albumin was used as a chiral selector reagent for synthesizing the CDs, the sensor device represented excellent selectivity to identify enantiomeric species of AAs. This is the first optical array device that can simultaneously discriminate AAs and several of their enantiomers. We employed various statistical and chemometric methods to analyze the digital data library collected by Image J software, including principal component analysis (PCA), linear discriminant analysis (LDA), and hierarchical cluster analysis (HCA). Twenty AAs could be well distinguished at various concentrations (10.00, 5.00, 2.50, and 1.25 mM). The colorimetric patterns were highly repeatable and were characteristic of individual AAs. Besides qualitative analysis, the designed μPAD-based optical tongue represented quantitative analysis ability, e.g., for lysine in the concentration ranges of 0.005–20.0 mM with a detection limit of 1.0 × 10−6 M and for arginine in the concentration range of 0.12–20.00 mM with a detection limit of 80.0 × 10−6 M. In addition, the binary, ternary, and quaternary mixtures of AAs could also be well recognized with this sensor. [ABSTRACT FROM AUTHOR]

COVID-19 has caused global health problems, and so rapid diagnosis is crucial to slow spread of the disease. Herein, a novel lab-on-paper screening method for SARS-CoV-2 Omicron BA.2 variant was developed using a gold nanoparticle-based colorimetric biosensor along with sensitive detection of SARS-CoV-2 antigen using laser desorption ionization-mass spectrometry (LDI-MS). As a result of antigen–antibody interaction, in the presence of SARS-CoV-2 antigen the gold nanoparticles undergo aggregation and change color from red to light purple, allowing for rapid determination of SARS-CoV-2 antigen with the naked eye. Furthermore, the lab-on-paper method can be directly applied as a substrate for sensitive quantitation of SARS-CoV-2 antigen in saliva using LDI-MS without the use of a conventional organic matrix and sample preparation. LDI-MS offers early diagnosis with high sensitivity, rapidity without sample preparation and lower cost per test compared with reverse transcriptase-PCR, which is crucial for preventing mortality in patients with underlying conditions. This method showed linearity over 0.01–1 μg mL−1 covering the cut-off value of 0.048 μg mL−1 for COVID-19 detection in human saliva. Moreover, a colorimetric sensor for urea was also fabricated in-parallel, for prediction of COVID-19 severity in patients with chronic kidney disease. The color change upon increasing urea concentration directly reflected kidney damage, which is related to increasing risk of mortality among patients with COVID-19. Hence, this platform might be a potential device for non-invasive diagnosis of SARS-CoV-2 Omicron BA.2 variant, which is the variant of most concern because it is transmitted more rapidly than the original SARS-CoV-2 virus and the Delta variant. [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman spectroscopy (SERS) is an emerging analytical technique for chemical analysis, which is favourable due to its combination of short measurement time, high sensitivity and molecular specificity. However, the application of SERS is still limited, largely because in real samples the analyte is often present in a complex matrix that contains micro/macro particles that block the probe laser, as well as molecular contaminants that compete for the enhancing surface. Here, we show a simple and scalable spray-deposition technique to fabricate SERS-active paper substrates which combine sample filtration and enhancement in a single material. Unlike previous spray-deposition methods, in which simple colloidal nanoparticles were sprayed onto solid surfaces, here the colloidal nanoparticles are mixed with hydroxyethyl cellulose (HEC) polymer before application. This leads to significantly improved uniformity in the distribution of enhancing particles as the film dries on the substrate surface. Importantly, the polymer matrix also protects the enhancing particles from air-oxidation during storage but releases them to provide SERS enhancement when the film is rehydrated. These SERS-paper substrates are highly active and a model analyte, crystal violet, was detected down to 4 ng in 10 μL of sample with less than 20% point-by-point signal deviation. The filter paper and HEC effectively filter out both interfering micro/macro particles and molecular (protein) contaminants, allowing the SERS-paper substrates to be used for SERS detection of thiram in mud and melamine in the presence of protein down to nanogram levels without sample pre-treatment or purification. [ABSTRACT FROM AUTHOR]

The effective integration of nanomaterials with underlying current collectors is a key factor affecting the performance of nonenzymatic glucose sensors, where an inappropriate integration structure often leads to poor electron transport and instability. In this work, a seamless integrated electrode was constructed by the in situ immobilizing of a nickel-based metal-organic framework (Ni-MOF) on a three-dimensional (3D) conductive nickel foam (NF) for highly sensitive and durable glucose sensing. Facilitated by a rapid microwave-assisted reaction, a robust interfacial interaction between the Ni-MOF and the substrate was established through in situ conversion from nickel oxide (NiO). The fabricated Ni-MOF/NF electrode exhibits an excellent limit of detection (LOD) of 2.65 μM and an impressive sensitivity (14.31 mA cm-2 mM-1) within the linear range (4-576 μM), which is significantly boosted compared with that of an electrode prepared by a typical drop-casting method (3.56 mA cm-2 mM-1 in 4-1836 μM). Characterization and electrochemical tests reveal that this integrated structure on the one hand contributes to fast electron transport and thus has enhanced sensitivity and on the other hand leads to exceptional durability with its structural integrity maintained under bending, shaking, and ultrasonication. Moreover, this seamless integration method was also employed to immobilize the Ni-MOF converted from the pre-chemically deposited NiO layer on another type of substrate, 3D carbon paper (CP), demonstrating the versatility of this facile strategy in creating diverse electrochemical electrodes for applications beyond glucose sensing. [ABSTRACT FROM AUTHOR]

The development of flexible current collectors as an indispensable component in energy storage devices has been in strong demand for the ever-growing market of flexible and wearable electronics. Herein, flexible and conductive paper-based current collectors are fabricated by directly depositing a metallic Ni layer composed of spiny Ni nanospheres of 400 nm diameter on the surface of filter paper via electroless deposition. The metallic paper shows excellent electric and mechanical properties: the sheet resistance is 2.7 Ω cm−2 (R0 = 0.8 Ω cm−2) after 5000 bending cycles and the mass density is only 0.35 g cm−3. MnO2 is selected as an electrode active material to explore the role of flexible and conductive paper-based current collectors in supercapacitors. Electrochemical results reveal that the largest areal specific capacitance is 1095 mF cm−2 at 1 mA cm−2 and the excellent electrochemical performance can be attributed to the hierarchical porous fibre structure of paper and the lower contact resistance between the active material and the current collector. Note that the approach can be applied to an enlarged size of metallic conductive paper or textile, presenting a simple and feasible method to fabricate flexible current collectors in a large scale. [ABSTRACT FROM AUTHOR]

The combination of electron-deficient viologen ligands with electron-rich POMs is a typical acceptor–donor system that has recently received much attention. Under solvothermal and hydrothermal conditions, by introducing three symmetric viologen ligands into POM-based hybrid materials, we successfully constructed four POMs–viologen inorganic–organic hybrid compounds, namely (1,3-bcbpy)2·(δ-Mo8O26) (1) (1,3-bcbpy·2Cl = 1,1′-bis(3-carboxybenzyl)-4,4′-bipyridine dichloride), {CoII(1,4-bcbpy)2(H2O)2[H2(β-Mo8O26)]}·2H2O·2CH2O (2), (1,4-bcbpy)2·(δ-Mo8O26)·2H2O (3) (1,4-bcbpy·2Cl = 1,1′-bis(4-carboxybenzyl)-4,4′-bipyridine dichloride, CH2O = formaldehyde), and {CuII(1,1-pmbby)2(H2O)[H2(β-Mo8O26)2]}·5H2O·C2H7N (4) (1,1-pmbby·2Cl = 1,1′-[1,4-phenylbis(methylene)]bis-(4,4′-bipyridine)dichloride, C2H7N = dimethylamine). These four compounds exhibit different fascinating structures, especially compound 4 is a typical metal–organic framework. Compounds 1–4 exhibit good discoloration behaviors under various external stimuli. For example, compounds 1–4 showed a positive response to the irradiation from a 300 W Xe lamp. When a positive voltage was applied to the ECD based on compounds 1–4, 1/2/3/4-ECD underwent a significant color conversion. What's more, compound 4 also showed obvious discoloration results after heating. In a word, 1–4 are multifunctional discoloration materials under different external stimuli. In addition, the coated filter paper prepared based on compound 3 can be used as a new printing material medium and can be successfully applied in erasable inkless printing and dual anti-counterfeiting. [ABSTRACT FROM AUTHOR]

The global efforts in electrifying our society drive the demand for low-cost and sustainable energy storage solutions. In the present work, a novel material concept was investigated to enable fabrication of several 10 meter-long rolls of supercapacitor paper electrodes on a pilot-scale paper machine. The material concept was based on cationized, cellulose-rich wood-derived fibres, conducting polymer PEDOT:PSS, and activated carbon filler particles. Cationic fibres saturated with anionic PEDOT:PSS provide a conducting scaffold hosting the activated carbon, which functions as the active charge-storage material. The response from further additives was systematically investigated for several critical paper properties. Cellulose nanofibrils were found to improve mechanical properties, while carbon black enhanced both the conductivity and the storage capacity of the activated carbon, reaching a specific capacitance of 67 F g−1. This pilot trial shows that "classical" papermaking methods are fit for the purpose and provides valuable insights on how to further advance bio-based energy storage solutions for large-scale applications. [ABSTRACT FROM AUTHOR]

The fast and precise detection of potential allergen-specific immunoglobulin E (sIgE) is imperative for the diagnosis and appropriate treatment of allergic diseases. In this study, we have successfully fabricated a novel paper-based immunoassay device for the detection of sIgE in allergic diseases. We used Can f 1, one of the main dog allergens, as a model allergen to detect sIgE in human sera. To achieve excellent performance, the experimental parameters were optimized. Further, we extended this device for potential applications in the clinical diagnosis of allergic diseases: worthwhile clinical performance in the detection of allergens was achieved as compared to that achieved by commercial enzyme-linked immunosorbent assay (ELISA) kit. Therefore, it was proven that this strategy has the advantages of high-throughput, rapid, sensitive, and highly accurate detection of trace amounts of sIgEs. Furthermore, by simply changing the antigen and antibody, this device could be used for the high-throughput detection of other allergens, so as to achieve multiallergen detection and appropriate desensitization therapy, thereby making it promising in the determination of allergic diseases in clinics.

Managing food contamination from bacteria has been an ongoing issue in the public health and industrial fields. Enzymatic substrates possessing optical properties, e.g. fluorescence or color manifestation, are widely exploited in pathogenic/non-pathogenic bacteria culture methods. Recently, various chromogenic substrates have been utilized in the development of point-of-care diagnostic tools. Herein, four types of chromogenic substrates were exploited to develop paper-based sensors for major foodborne pathogens. We designed a compact sized three-dimensional paper device with a simple user interface. By inserting functional layers in the middle of multilayers, pre-lysis and pH regulation steps were excluded and the analysis time was subsequently reduced, while only one sample droplet was needed for the whole analysis process. After the enzymatic reactions had proceeded, target-specific colors appeared. When it was combined with enrichment, 101 cfu mL-1 of pathogens were successfully detected in 4-8 hours, while those in milk samples were readily sensed in 12 hours. The proposed bacteria sensor exhibited great advantages of low cost, portability and simple operation, while showing a respectable limit-of-detection as low as 101 cfu mL-1 and below. Significantly, we emphasize that it takes fewer steps than existing methods and provides a reduced analysis time owing to the layer functionalization.

We developed a multiplexed point-of-care immunodiagnostic assay for antibody detection in human sera made through the vertical stacking of functional paper layers. In this multiplexed vertical flow immunodiagnostic assay (xVFA), a colorimetric signal is generated by gold nanoparticles captured on a spatially-multiplexed sensing membrane containing specific antigens. The assay is completed in 20 minutes, following which the sensing membrane is imaged by a cost-effective mobile-phone reader. The images are sent to a server, where the results are rapidly analyzed and relayed back to the user. The performance of the assay was evaluated by measuring Lyme-specific antibodies in human sera as model target antibodies. The presented platform is rapid, simple, inexpensive, and allows for simultaneous and quantitative measurement of multiple antibodies and/or antigens making it a suitable point-of-care platform for disease diagnostics.

A paper-based platform was investigated in which the selective detection of oligonucleotide targets by hybridization was accomplished via the enhancement of fluorescence emission from intrinsically labeled DNA probes that were immobilized on the surface of quantum dots (QDs). Multiple copies of a derivative of thiazole orange, an intercalating dye known to form non-emissive dimers, were conjugated to single-stranded oligonucleotide probes. Dimerization resulted in the formation of H-aggregates where excitonic interactions led to the suppression of fluorescence. The hybridization of the oligonucleotide probe with a complementary target resulted in the enhancement of fluorescence emission as the dimers dissociated and the dyes preferentially intercalated with the duplex. The detection of oligonucleotide targets using this configuration eliminated the need for labeling the target strands, and fluorescence intensity was proportional to the extent of hybridization. In addition, the dye molecules were excited using Foerster Resonance Energy Transfer (FRET) from QD donors, which resulted in improved selectivity and allowed for ratiometric detection. A solution-phase hybridization assay based on similar operational principles has been previously reported, and this new work investigated the advantages offered for this transduction scheme using paper-based solid-phase substrates. QD-probe conjugates were immobilized in sufficient density on the paper matrix to provide for multiple-donor-multiple-acceptor interactions that resulted in a 20-fold enhancement of acceptor emission compared to the solution-based assay, providing a limit of detection of 0.1 pmol. The paper-based assay provided for the reduction of the time needed for sample preparation and data acquisition, demonstrated that transduction was possible in a complex matrix (goat serum) without compromising on the performance observed in buffer solution, and that oligonucleotides generated from standard PCR amplification could be detected.

In this study, we demonstrate a three-dimensional surface-modified origami-paper-based analytical device (3D-soPAD) for immunoassay applications. The platform enables the sequential steps of immunoassays to be easily performed using a folded, sliding paper design featuring multiple pre-stored reagents, allowing us to take advantage of the vertical diffusion of the analyte through the different paper layers. The cellulose substrate is composed of carboxymethyl cellulose modified with N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide, which provide covalent bonding sites for bio-recognition molecules. After the optimization of the operation parameters, we determined the detection limit of the 3D-soPAD for human immunoglobulin G (HIgG) which can be as low as 0.01 ng mL-1, with a total turnaround time of 7 min. In order to study the long-term storage of the platform, anti-HIgG horseradish peroxidase (aHIgG-HRP) conjugates were stored by freeze-drying in sugar matrices composed of 10% sucrose/10% trehalose (w/w%) on the paper device, retaining 80% of their activity after 75 days of storage at 4 °C. To evaluate the performance of the paper device using real samples, we demonstrated the detection of protein A (a biomarker for Staphylococcus aureus infection) in highly viscous human synovial fluid. These results show that the proposed 3D-soPAD platform can provide sensitive, high-throughput, and on-site prognosis of infection in resource-limited settings.

Rapid detection of pesticides in fruits is an ongoing challenge. The objective of the present study was to develop novel fluorescent microfluidic paper chips for specific recognition and sensitive detection of the pesticide 2,4-D through the electron-transfer-induced fluorescence quenching mechanism. CdTe quantum dots (QDs) were deposited onto cellulose paper (base material) to yield imprinted paper chips (paper@QDs@MIPs). This method allows the transferability of the molecularly imprinted fluorescence sensor from the liquid phase to the solid phase (paper base) for rapid and portable analysis. The resultant imprinted paper chips were effectively characterized, and they exhibited ideal ordered spatial network structure, chemical stability, and fluorescence property. The paper@QDs@MIPs showed that 2,4-D binding significantly reduced the fluorescence intensity within less than 18 min, and it achieved satisfactory linearity in the range of 0.83-100 μM and high detectability of 90 nM. The recognition specificity for 2,4-D relative to its analogues was shown, and the imprinting factor was 2.13. In addition, the recoveries of the spiked bean sprouts at three concentration levels ranged within 94.2-107.0%, with a relative standard deviation of less than 5.9%. Collectively, the device provided an effective platform for rapid recognition, convenience, and detection of trace food pollutants in complex matrices, thereby ensuring food safety and further promoting surface imprinting studies.

Paper-based microfluidics was initially developed for use in ultra-low-cost diagnostics powered passively by liquid wicking. However, there is significant untapped potential in using paper to internally guide porous microfluidic flows using externally applied pressure gradients. Here, we present a new technique for fabricating and utilizing low-cost polymer-laminated paper-based microfluidic devices using external pressure. Known as microfluidic pressure in paper (μPiP), devices fabricated by this technique are capable of sustaining a pressure gradient for use in precise liquid handling and manipulation applications similar to conventional microfluidic open-channel designs, but instead where fluid is driven directly through the porous paper structure. μPiP devices can be both rapidly prototyped or scalably manufactured and deployed at commercial scale with minimal time, equipment, and training requirements. We present an analysis of continuous pressure-driven flow in porous paper-based microfluidic channels and demonstrate broad applicability of this method in performing a variety of different liquid handling applications, including measuring red blood cell deformability and performing continuous free-flow DNA electrophoresis. This new platform offers a budget-friendly method for performing microfluidic operations for both academic prototyping and large-scale commercial device production. [ABSTRACT FROM AUTHOR]

Uniformly dispersing silver nanowires (AgNWs) in polymer matrices is of paramount importance for developing high-performance electromagnetic interference (EMI) shielding materials. Herein, new flexible and robust high-efficiency bacterial cellulose (BC)-based EMI shielding papers were developed via a modified step-by-step in situ biosynthesis method, in which, AgNWs were well distributed in the BC network. The BC nanofibers and AgNWs could form an effective entangled network with hydrogen bonding, efficiently strengthening the produced BC/AgNW papers. An electrical conductivity of 608 365 S m−1 was achieved for a BC/AgNW paper with a AgNW content of 36.5 wt%, which is superior to almost all AgNW-containing papers reported so far. Moreover, the BC/AgNW paper could sustain mechanical deformation and vigorous washing, without losing electrical conductivity. Additionally, this paper presents an ultrahigh specific EMI shielding effectiveness of ∼6400 dB mm−1, which is higher than almost all previously reported AgNW-based polymer composites. The proposed approach in this study provides a facile and scalable fabrication route for producing flexible and highly conductive BC/AgNW papers, which are of great potential as electrically conductive components and EMI shielding elements in advanced applications. [ABSTRACT FROM AUTHOR]

Flexible energy storage devices are of significant interest for wearable device applications. In this regard, paper, which is thin, light, flexible, and highly porous, has emerged as a next-generation energy-storage material. Here, we introduce a facile technology for fabricating a supercapacitor based on a single sheet of paper, in which the electrodes are vertically separated by the patterning of hydrophobic barriers. The positive and negative electrodes can be simultaneously sectionalized as active layers and current collectors in a single-layer porous paper supercapacitor, such that the gel electrolyte infiltrates the device without any additional assembly. The solid-state supercapacitor with vertically layered electrodes exhibits a large areal capacitance of 560.2 mF cm−2 at 0.2 mA cm−2 and stable flexibility and foldability. The maximum power and energy densities were 1.597 mW cm−2 and 28.74 μW h cm−2, respectively, which highly exceed those of previously reported multi-sheet paper-based supercapacitors. [ABSTRACT FROM AUTHOR]

Recently, paper has gained traction in the biotechnology research field due to its ability to be a substrate for 3D cell culture. In this work, we demonstrate the application of paper-based 3D cell culture for rapid and easy screening of the effect of natural compounds on melanin production. Whatman No. 1 filter paper was used as the substrate for B16F10 melanoma cell culture. The use of paper is beneficial for supporting the 3D structure of cells, which makes the result more reliable due to the similarity to in vivo conditions. Furthermore, paper is beneficial for melanin observation due to melanin's black color, which is easily in situ visualized after it is cultured on white paper. Matrigel was used to encapsulate cells before being pipetted onto the paper to prevent the passing of cells through paper pores. The intensity of melanin can then be observed with the naked eye and analyzed by scanning the paper. The analysis process took only 20 minutes, which is faster than that of the conventional absorbance spectroscopy, owing to the elimination of centrifugation, melanin solubilization, and the absorbance measurement step. The color intensity on the paper showed a direct proportion with increased α-MSH concentrations, confirming that the color on the paper was melanin. The 3D structure of cells was confirmed by using a scanning electron microscope. To demonstrate the application of the paper-based scaffold, paper-based 3D cell culture was used for screening the effects of Kojic acid and Arbutin on melanin production, which showed increased anti-melanogenesis effects with increased concentrations of natural compounds. High cell viability was observed over 120 hours. In conclusion, the developed paper-based scaffold can be used for screening the effect of natural compounds on melanin production, as a rapid and simple method with low cost.

Cellular movement is essential in the formation and maintenance of healthy tissues as well as in disease progression such as tumor metastasis. In this work, we describe a paper-based Transwell assay capable of quantifying cellular invasion through an extracellular matrix. The paper-based Transwell assays generate similar datasets, with equivalent reproducibility, to commercially available Transwell assays. With different culture configurations, we quantify invasion: upon addition of an exogenous factor or in the presence of medium obtained from other cell types, in an indirect or direct co-culture format whose medium composition is dynamically changing, and in a single-zone or parallel (96-zone) format.

A novel paper-based analytical device (PAD) was fabricated and developed for the simple and rapid determination of the albumin to creatinine ratio (ACR) in urine samples. The detection was based on a colorimetric reaction using bromocresol green (BG) in a phosphate buffer (PB) at pH 4 for the determination of albumin (AL) and creatinine (CR). BG changes color from greenish-yellow to bluish-green in the presence of AL and/or CR. Picric acid (PA) in 0.25 M NaOH was used to detect CR, and PA changes color from yellow to orange. Under the optimal conditions, the working range was 10 to 350 mg dL-1 with a detection limit of 7.1 and 5.4 mg dL-1 for AL + CR and CR detection, respectively. The repeatability was evaluated, and the %RSD value was less than 8.23 (n = 10). The ACR was obtained by calculating the AL and CR colorimetric results. Finally, the proposed devices were applied to the determination of AL, CR, and ACR in urine samples. The results obtained by the developed PADs were in good agreement with the standard method and demonstrated the method could reliably measure AL, CR, and ACR. The proposed method provides a low-cost, simple, sensitive, and promising tool for diagnostic identification assay for chronic kidney disease (CKD).

In this work, a versatile point-of-care assay platform based on a microfluidic paper-based analytic device (μPAD) was developed for the simultaneous detection of multiple targets. The μPAD with a central zone and six test zones is fabricated by a simple and inexpensive wax printing method. A flower-like hybrid nanocomplex synthesized with specific dual enzymes and Cu3(PO4)2 inorganic nanocrystals is spotted in the test zones on the μPAD, followed by the introduction of assay targets. Using dual-enzyme inorganic hybrid nanoflowers in the μPAD as nanobiocatalysts, which preserve the activity and enhance the stability of the enzymes, based on the H2O2-mediated catalytic oxidizing chromogenic reaction produced by glucose/uric acid, the developed multiplex paper-based nanobiocatalytic system is demonstrated to enable simultaneous and sensitive detection of glucose and uric acid with a detection limit of 60 and 25 μM, respectively. More importantly, it has been successfully used for detecting glucose and uric acid levels in human whole blood samples. The developed multiplex paper-based nanobiocatalytic system features very easy fabrication and operation, low cost, and high sensitivity and has promising prospects for a clinical multianalyte point-of-care test.

Microfluidic paper-based analytical devices (μPADs) have been widely explored for point-of-care testing due to their simplicity, low cost, and portability. μPADs with multiple-step reactions usually require precise flow control, especially flow-delay. This paper reports the numerical, mathematical, and experimental studies of flow delay through wax valves surrounded by PDMS walls on paper microfluidics. The predried surfactant in the sample zone diffuses into the liquid sample which can therefore flow through the wax valves. The delay time is automatically regulated by the diffusion of the surfactant after sample loading. The numerical study suggested that both the elevated contact angle and the reduced porosity and pore size in the wax printed region could effectively prevent water but allow liquids with lower contact angles ( e.g. , surfactant solutions) to flow through. The PDMS walls fabricated using a low-cost liquid dispenser effectively prevented the leakage of surfactant solutions. By controlling the quantity, diffusion distance, and type of the surfactant predried on the chip, the system successfully achieved a delay time ranging from 1.6 to 20 minutes. A mathematical model involving the above parameters was developed based on Fick's second law to predict the delay time. Finally, the flow-delay systems were applied in sequential mixing and distance-based detection of either glucose or alcohol. Linear ranges of 1-100 mg dL -1 and 1-40 mg dL -1 were achieved for glucose and alcohol, respectively. The lower limit detection (LOD) of glucose and alcohol was 1 mg dL -1 . The LOD of glucose was only 1/11 of that detected using μPADs without flow control, indicating the advantage of controlling fluid flow. The systematic findings in this study provide critical guidelines for the development and applications of wax valves in automatic flow delay for point-of-care testing.

The transfusion of ABO-compatible blood with blood with an unknown phenotype may result in alloimmunization, particularly in multitransfused patients. Minor blood-group phenotyping and the selection of negative blood for specific antigens reduce post-transfusion complications. With this study, a device called the DROP and READ instrument was developed with a PAD (paper-based device) and various software to phenotype ABO, Rh (D, C, c, E, e), and Mi a antigens. EDTA (Ethylene diamine tetra-acetic acid) blood samples were collected from donors, volunteers, and newborns, and were then tested with the DROP and READ instrument according to the lateral flow and RBC agglutination principle. The results were compared with those obtained by using a routine column agglutination test or the tube method. Results: a total of 205 samples were tested (150 from EDTA blood donors, 50 from EDTA blood volunteers, and 5 from the cord blood of newborns). The device yielded 100% accuracy, sensitivity, and specificity, a positive predictive value, and a negative predictive value when interpreting the ABO, Rh (D, C, c, E, e), and Mi a antigens. The DROP and READ instrument is developed to automatically interpret the results, and the device provided endpoint results without centrifugation and prevented misinterpretations from human error.

A new Cd II -based luminescent metal-organic framework (LMOF) with the formula {[Cd(BIBT)(NDC)]·solvents} n (JXUST-32, BIBT = 4,7-bi(1 H -imidazol-1-yl)benzo-[2,1,3]thiadiazole and H 2 NDC = 2,6-naphthalenedicarboxylic acid) was successfully synthesized by a solvothermal method. JXUST-32 shows a two-dimensional (4,4)-connected network and exhibits significant fluorescence red shift and slight enhancement for H 2 PO 4 - and CO 3 2- sensing with detection limits of 0.11 and 0.12 μM, respectively. In addition, JXUST-32 has good thermal stability, chemical stability and recyclability. Significantly, JXUST-32 represents a fluorescence red-shift dual response MOF sensor for H 2 detection and the analytes can be identified by the naked eye, aerosol jet printing filter paper, light-emitting diode beads and luminescent films.4 - and CO 3 2- detection and the analytes can be identified by the naked eye, aerosol jet printing filter paper, light-emitting diode beads and luminescent films.

Here, we report an inkjet-printed graphene paper electrode (IP-GPE) for the electrochemical analysis of mercuric ions (Hg(ii)) in industrial wastewater samples. Graphene (Gr) fabricated on a paper substrate was prepared by a facile solution-phase exfoliation method in which ethyl cellulose (EC) behaves as a stabilizing agent. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were utilized to determine the shape and multiple layers of Gr. The crystalline structure and ordered lattice carbon of Gr were confirmed by X-ray diffraction (XRD) and Raman spectroscopy. The nano-ink of Gr-EC was fabricated on the paper substance via an inkjet printer (HP-1112) and IP-GPE was exploited as a working electrode in linear sweep voltammetry (LSV) and cyclic voltammetry (CV) for the electrochemical detection of Hg(ii). The electrochemical detection is found to be diffusion-controlled illustrated by obtaining a correlation coefficient of 0.95 in CV. The present method exhibits a better linear range of 2-100 μM with a limit of detection (LOD) of 0.862 μM for the determination of Hg(ii). The application of IP-GPE in electrochemical analysis shows a user-friendly, facile, and economical method for the quantitative determination of Hg(ii) in municipal wastewater samples., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

We describe a method for the differentiation of carboxylate anions on disposable paper supports (common printer paper, filter paper, chromatography paper), based on differential patterns of interactions between carboxylates and a fluorescent sensing system. The sensor was built from commercially available components, namely a polycationic fifth generation amine-terminated poly(amidoamine) dendrimer (PAMAM G5) and a small organic fluorophore (calcein) through non-covalent interactions. The assay’s physical dimensions were chosen to conform to the microwell plate standard so detection could be carried out on widely available plate reader instrumentation. The sensing complex was first deposited in spots on a paper support to prepare the sensor strip; a carboxylate solution was then loaded on each spot. Nuanced changes in fluorescence were associated with carboxylate binding to the PAMAM dendrimer, characteristic of the structure and affinity of each carboxylate. Such signal changes, interpreted through Linear Discriminant Analysis (LDA), contained enough information to recognize and successfully discriminate most anions in the panel. Among the substrates we tested, chromatography paper was the most promising. The relationship between the structure of the carboxylates and the patterns giving rise to their differentiation was also discussed. Finally, the long-term stability (“shelf life”) of the pre-assembled [calcein·dendrimer] sensing system was found to be excellent when deposited on paper support. [ABSTRACT FROM AUTHOR]

In this work, paper-based flexible X-ray detectors were developed. Outstanding detection performance and high stability were realized by combining the intrinsic flexibility of the PbI2 nanocrystal, and the bendability of cellulose fiber paper. The devices were prepared using a scalable solution infiltration method and a screen-printing method. The PbI2 nanocrystal was coating onto the fiber instead of filling the micropore between the fibers. This special microstructure suppresses the effect of the carrier lateral diffusion by restricting the transport of the photoexcited carriers along the longitudinal direction of fibers, which promotes carrier transport, and improves photodetection performance. All of the pixels showed a high consistency of sensitivity, and a high signal-to-noise ratio, which ranged from 76.7 to 78.3 mC Gy-1 cm-2, and 296.4 to 327.3, respectively. In addition, benefitting from the unfilled micropores which serve as a stress buffer zone, the devices reveal high flexibility when the composite structure is in tension or compression. After 1000 bending cycles, no cracks were found in the nanocrystalline layer on the fibers, and the photocurrent was maintained at over 87%. In addition, a linear array X-ray imager was successfully implemented using the as-fabricated devices. [ABSTRACT FROM AUTHOR]

Electrochemical oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) has received increasing attention as it is an eco-friendly strategy for synthesizing a key monomer for the production of bio-based plastics. Developing efficient, low-cost and stable electrocatalysts is crucial for this electrochemical reaction. In this work, we have reported a facile process for the synthesis of hybrid nanosheet-structured NiCo2O4 on carbon fiber paper (NiCo2O4-CFP) for the efficient electrochemical conversion of HMF into FDCA. As a non-noble binary metal-based catalyst, NiCo2O4-CFP featured a nanosheet network and 3D nanosheet flower-like microspheres, showing 94.3% selectivity and 89.6% faradaic efficiency (FE) for FDCA, which outperformed its single component metal oxides NiO-CFP and Co3O4-CFP. And it also exhibited relatively high stability by maintaining over 80% FE after four successive cycles. The proposed mechanism suggested that the synergistic effect of Ni and Co elements in NiCo2O4 could facilitate HMF oxidation. [ABSTRACT FROM AUTHOR]

Triboelectric nanogenerators (TENGs) have been widely used for self-powered gas sensors recently. However, limitations such as low sensitivity especially for trace concentrations of NH3 and narrow detection ranges inevitably pose serious challenges. Herein, a kind of highly sensitive self-powered gas sensor based on a PANI/cellulosic hierarchical structure (PC-TENG) was developed to detect NH3 gas. The hierarchical structure provides excellent gas permeability and huge numbers of gas adsorption sites. Meanwhile, the most effective structure design of the integrated self-powered NH3 sensors (PANI acts as the electrode/tribo-material) was identified by a comparison of different structure designs (PANI plays a single role of the electrode or tribo-material, or double roles of the both). Benefitting from the abundant gas adsorption sites, and the coordinate regulation of the PANI's surface tribo-state and impedance caused by protonation–deprotonation of PANI, the rationally designed PC-TENG exhibits outstanding sensing properties, with a minimum detection limit as low as 100 ppb and a maximum limit of 500 ppm, wherein the maximum output voltage and current of the PC-TENG are 23 V and 0.17 μA, respectively. And the sensitivity of the PC-TENG was up to 45.41% ppm−1 from 0.1 to 1 ppm, and 15.17% ppm−1 from 1 to 50 ppm. In particular, the sensitivity for trace concentrations of NH3 (0.1 to 50 ppm) is the highest value among reported studies. In addition, the mature processing technique of commercial nitro-cellulosic paper and its eco-friendly nature further provide the feasibility of large-scale production and application of environmentally friendly self-powered NH3 sensors. [ABSTRACT FROM AUTHOR]

Viologens exhibit excellent color responses to external stimuli owing to their desirable redox properties. They have been widely studied in electrochromic and photoluminescent materials. Generally, polymeric materials have better processing properties and longer service life than small organic molecules. Herein, a viologen-containing polyurethane was synthesized and used to prepare an electrochromic device and a paper-based amine detector. The obtained electrochromic device displayed an excellent electrochromic behavior when subjected to an external voltage as low as 1.0 V. Moreover, the designed paper-based amine detector exhibits a highly sensitive color-change response when exposed to liquid amine solutions (down to 1 ppm concentration) or gaseous ammonia. The results of this study demonstrated that the developed viologen-containing polyurethane exhibits excellent electrochromic performance and the designed amine-detecting paper chips are an excellent tool for amine detection. [ABSTRACT FROM AUTHOR]

Pesticide residues are a serious problem towards agriculture, environment and food safety, so it is highly desirable to develop a swift, efficient and portable pesticide detection method. A fluorescence visual sensing method for glyphosine based on a nitrogen-doped biomass carbon quantum dot (N-CQD) paper-based sensor was developed. The fluorescence signal was quenched by Fe3+ in a static quenching process, and then the fluorescence of N-CQDs was recovered after adding glyphosine. Under the optimal experimental conditions and when tested with a fluorescence spectrofluorometer, the detection of glyphosine showed a two-stage linear pattern in the range of 0.1–0.6 μM and 0.6–1.6 μM with a detection limit of 0.075 μM. Then, the RGB values of different concentrations of glyphosine on the filter paper chip were detected by the software of the smartphone-color identifier. The logarithm of the glyphosine concentration was linearly related to the G value of RGB in the range of 0.25–10.00 mM and with a detection limit of 0.15 mM. The method was applied to measuring glyphosine-spiked juice and flour samples, and the recovery rates were 87.60–112.69% and 93.27–105.83%, respectively. The proposed N-CQDs/Fe3+ system had wide applications, and it was expected to be fast and effective at detecting pesticide residues. [ABSTRACT FROM AUTHOR]