Search

A paper-based analytical device (PAD) with an integrated composite electrode has been designed and fabricated for non-enzymatic creatinine sensing. Reduced graphene oxide (rGO) was employed to modify the PAD so that it could function as a solid-contact transducer. A new macrocyclic pyrido-hexapeptide derivative was made and used as a special ionophore in the creatinine membrane sensor. The synthesized PAD showed a detection limit of 1.0 µM (S/N = 3) and a potentiometric response towards creatinine throughout a log-linear range of 2.0 µM–10 mM (R2 = 0.9998). The sensor shows significant selectivity for a few related substances, including ephedrine, codeine, ketamine, caffeine, urea, urate, carbinoxamine, and dextromethorphan. It has been established that the testing method is appropriate for the direct potentiometric detection of creatinine in a variety of human urine sample types. When an indicating electrode and a reference electrode are put on the same flexible disposable, this lets applications with a small sample volume be done. For point-of-care creatinine measurement, the developed paper-based analytical equipment is a good choice because it is affordable, easily accessible, and self-pumping (especially when combined with potentiometric detection). [ABSTRACT FROM AUTHOR]

A paper-based analytical device (PAD) is presented with colorimetric/electrochemical dual readouts for the simultaneous sensing of total chromium (Cr) and hexavalent chromium (Cr(VI)). This device consists of a homemade three-electrode system and a patterned paper chip, integrating multiple functions including electrochemical detection, fluid driving, online oxidation, and colorimetric detection. The fiberglass filter paper with a hydrophilic microchannel was used to achieve self-driving fluidics without external equipment. One end of the microchannel was integrated with a homemade three-electrode system to achieve sample loading and electrochemical detection. The middle region on the microchannel was modified with oxidizing reagents to perform online pretreatment, and the yield of Cr(III) oxidation can reach 97.9%, ensuring reliable colorimetric detection of total Cr at another end of the microchannel modified with chromogenic agents. With this device, the signals of Cr(VI) (the signal peak at 0.29 V vs. Ag/AgCl) and total Cr can be obtained in one single injection. After optimization, the limit of detection (LOD) of Cr(VI) and total Cr were 0.01 mg L−1 and 0.06 mg L−1 and the linear ranges were 0.05–3.0 mg L−1 and 0.2–3.0 mg L−1, respectively. The relative standard deviations (RSD) of the electrochemical testing of Cr(VI) results were in a range 1.3%–8.7% (n = 3), and the RSD values of the colorimetric testing of total Cr were between 0.7–9.2% (n = 3). The device's reliability was demonstrated by performing the practical speciation of Cr in tap water, river water, and electroplating wastewater while the recoveries obtained using the present method were in the range 93.5–106%. Overall, the proposed device provides high application prospect in the on-site rapid Cr speciation. [ABSTRACT FROM AUTHOR]

• Surface molecularly imprinted polymer with selective recognition capability to butachlor was fabricated. • A colorimetric paper chip combined with the smartphone was developed to detect butachlor in mung bean. • The sensor has highly selective and sensitive to butachlor with LOD is 1.43 ng/g. • The sensor is simple, cheap, portable and widely used for fast detection. A microfluidic paper chip colorimetric detection system based on surface molecular imprinting of zinc ferrite nanoparticles was established, and the detection images were obtained by smartphone for gray value analysis and determination of butachlor. The best functional monomers and addition ratio were selected by quantum chemical simulation calculation, the properties of the prepared molecularly imprinted polymers were analyzed, and the detection conditions were optimized. The linear range, sensitivity, and selectivity of the method were evaluated. The results showed that under the optimum conditions, the concentration of 2–80 ng/g had a good linear relationship (R2 is 0.9953), the detection limit was 1.43 ng/g, the specificity was good, and the whole detection process did not exceed 20 min. The microfluidic paper chip was applied to detect butachlor in mung bean samples. The results showed that the recovery was 93.4–106.4 %, and the relative standard deviation was less than 5.6 %. [ABSTRACT FROM AUTHOR]

A microcapillary grooved paper-based analytical device capable of dual-mode sensing (colorimetric and electrochemical detection) was demonstrated for analysis of viscous samples (e.g., human saliva). Herein, a hollow capillary channel was constructed via laser engraved micropatterning functions as a micropump to facilitate viscous fluidic transport, which would otherwise impede analysis on paper devices. Using salivary thiocyanate as a model analyte, the proposed device was found to exhibit a promising sensing ability on paper devices without the need for sample pretreatment or bulky instrumentation, as normally required in conventional methods used for saliva analysis. An extensive linear dynamic range covering detection of salivary thiocyanate for both high and trace level regimes (5 orders of magnitude working range) was collectively achieved using the dual-sensing modes. Under optimal conditions, the limit of detection was 6 μmol L−1 with a RSD of less than 5%. An excellent stability for the μpumpPAD was also observed for over 30 days. Real sample analysis using the proposed device was found to be in line with the standard chromatographic method. Benefitting from simple fabrication and operation, portability, disposability, low sample volume (20 μL), and low cost (< 1 USD), the μpumpPAD is an exceptional alternative tool for the detection of various biomarkers in saliva specimens. [ABSTRACT FROM AUTHOR]

Cyanide anion can be found in foodstuffs, tobacco smoke and a variety of types of waters, mainly originating from anthropogenic activities. Due to its highly toxic nature, several agencies have established limits for cyanide levels in water. Additionally, monitoring cyanide levels in biological samples, such as blood and urine, is crucial for obtaining clinical information about the health condition of patients. Therefore, there is a pressing need for the development of simple, cost-effective, and reliable analytical methods capable of quantifying cyanide at low concentrations. This study presents a novel analytical method for the selective and sensitive determination of cyanide based on analyte volatilization, pre-concentration via single-drop microextraction (SDME) using a selective reagent, and colorimetric quantification using a paper-based analytical device. For this, 10 mL of a liquid sample was acidified with phosphoric acid and the generated HCN was collected using a single drop of 3 μL of a palladium dimethylglyoximate solution (Pd (DMG) 2 2−) positioned in the flask headspace using a syringe. The reaction of Pd (DMG) 2 2− leads to the formation of Pd(CN) 4 2− and the demasking of the organic ligand. After 15 min of extraction time, the reagent drop was added to a paper-based analytical device that has been previously impregnated with 3 μL of nickel chloride, resulting in the formation of a red precipitate of nickel (II) dimethylglyoximate. Digital images of the paper-based device were captured and the red channel (R) was used for quantification purposes. Under optimized conditions, the method demonstrates a suitable linear relation (r2 > 0.99) ranging from 26 to 286 μg L−1 and a limit of detection of 5 μg L−1. As a proof of concept, cyanide levels were quantified in water and urine samples using this method. The proposed approach offers high sensitivity and selectivity while requiring only a small volume of reagents. Furthermore, it exhibits a high degree of portability for in-situ applications. A selective and sensitive method for the determination of cyanide using HS-SDEM. [Display omitted] • Cyanide in liquid samples was determined by combining HS-SDME and digital image analysis. • Colorimetric reaction is performed on a microfluidic paper-based analytical device. • The reagent is easy to prepare and highly selective for cyanide. • Under optimized conditions, a limit of detection of 5 μg L-1 was achieved. • The point-of-care device is suitable for cyanide determination in water and urine samples. [ABSTRACT FROM AUTHOR]

Herein we report the first two distance-based microfluidic paper-based analytical devices (μPADs) using fluorescence to quantify aluminum. In addition to their read-by-eye quantification, the devices are simple to fabricate, require no sample pretreatment or preconcentration, and have a shelf life of >5 months. The first device is designed in a "chemometer" format where the length of a fluorescent band linearly responds to an Al(III) concentration. The second device uses a radial design where the fluorescent diameter also linearly responds to an Al(III) concentration. The chemometer device has a detection limit of 2.5 ppm (100 μM) and a linear range from 2 to 54 ppm Al(III) (100 μM–1 mM), R2 = 0.989). The radial device has a detection limit of 0.9 ppm (33 μM) and a linear range from 2 to 24 ppm Al(III) (100–900 μM, R2 = 0.968). The utility of the μPADs were successfully demonstrated by measuring Al(III) in two water effluent samples from the Gold King Mine near Silverton, CO. Image 1 • Distance-based detection of Al(III) in water samples. • Radial and linear distance based detection demonstrated. • Method gives accurate results in natural waters. [ABSTRACT FROM AUTHOR]

The colorimetric sensor usually depends on enzyme-mediated signal amplification to achieve trace analysis of ochratoxin A (OTA) residues in food samples. However, the enzyme labeling and manual addition of reagents steps increased assay time and operation complexity, restricting their application in point-of-care testing (POCT). Herein, we report a label-free colorimetric device integrating a 3D paper-based analytical device and a smartphone as handheld readout for rapid and sensitive detection of OTA. Using vertical-flow design, the paper-based analytical device enables the specific recognition of target and self-assembly of G-quadruplex (G4)/hemin DNAzyme to be performed, then employs DNAzyme for transducing the OTA binding event signal into a colorimetric signal. The design of independent functional units, including biorecognition unit, self-assembly unit and colorimetric units, which can address crowding and disorder of biosensing interfaces and improve the recognition efficiency of aptamer (apta). In addition, we eliminated signal losses and nonuniform coloring by introducing carboxymethyl chitosan (CMCS) to obtain perfectly focused signals on colorimetric unit. On the basis of parameter optimization, the device exhibited a detection range of 0.1–500 ng/mL and a detection limit of 41.9 pg/mL for OTA. Importantly, good results were obtained in spiked real samples, indicating applicability and reliability of developed device. [Display omitted] • A label-free and enzyme-free colorimetric 3D μPAD was designed with a smartphone as a readout device. • The G4/hemin DNAzyme with high peroxidase-like activity was acted as signal amplification element. • The device displayed low detection limit of 41.9 pg/mL for OTA. • The favorable practical applicability was obtained for OTA detection in real samples. [ABSTRACT FROM AUTHOR]

[Display omitted] • A smartphone/PAD system was developed for iodate measurement in table salt. • The developed method performed comparably with commercial test kits. • The results of the present method agree well with the reference method. • The proposed method supports the green analytical technique. A digital colorimetric sensor was developed for the on-site measurement of iodate in food-grade salt. It involved a paper-based analytical device (PAD) containing an immobilized iodide/starch reagent and a smartphone as the detection system. Iodate ions produce a blue-black coloration on the PAD, the smartphone captures a digital image of the PAD, and an installed mobile app performs an analysis to generate color values related to the intensity of the color in the PAD. Parameters in the image acquisition and PAD preparation were optimized, and a matrix-matched calibration plot was employed for quantification. The plot exhibited a linear response in the concentration range of 10 to 100 mg iodate kg−1 of salt, and a detection limit of 2.20 mg kg−1 was determined. The present method was applied to analyze real samples, and the results agreed well with those obtained using the reference method at the 95% confidence level. [ABSTRACT FROM AUTHOR]

A rapid, simple and affordable method for arsenic speciation analysis is described in this work. The proposed methodology involves in situ arsine generation, transfer of the volatile to the headspace and its reaction with silver nitrate at the detection zone of a paper-based analytical device (PAD). Thus, silver nitrate acts as a recognition element for arsine in the paper-based sensor. The chemical reaction between the recognition element and the analyte derivative results in the formation of a colored product which can be detected by scanning the detection zone and data treatment with an image processing and analysis program. Detection and injection zones were defined in the paper substrate by formation of hydrophobic barriers, thus enabling the formation of the volatile derivative without affecting the chemical stability of the recognition element present in the PAD. Experimental parameters influencing the analytical performance of the methodology, namely color mode detection, composition of the paper-based sensor and hydride generation and mass transfer conditions, were evaluated. Under optimal conditions, the proposed method showed limits of detection and quantification of 1.1 and 3.6 ng mL −1 , respectively. Remarkably, the limit of detection of the method reported herein was much lower than the maximum contaminant levels set by both the World Health Organization and the US Environmental Protection Agency for arsenic in drinking water, unlike several commercially available arsenic test kits. The repeatability, expressed as relative standard deviation, was found to be 7.1% (n = 8). The method was validated against the European Reference Material ERM ® -CA615 groundwater and successfully applied to the determination of As(III), As(V) and total inorganic As in different water samples. Furthermore, the method can be used for the screening analysis of total arsenic in waters when a cut-off level of 7 ng mL −1 is used. [ABSTRACT FROM AUTHOR]

[Display omitted] • 2k factorial designs were used to optimize the µPADs methods. • Interferences as proteins and carbohydrates were removed in situ on the µPAD. • The formation of ABTS radical on the µPAD was 90 % faster than the batch method. • Samples analysis was only of 5 min for total polyphenols and antioxidant capacity. • Non-significant differences between the proposed µPAD and batch method. A µPAD to determine the total polyphenol content (TPC) by Folin-Ciocalteau (FC) method, and antioxidant capacity by ABTS method, coupling an in-situ pretreatment zone with Carrez reagents is proposed. Conditions of FC, K 2 S 2 O 8 , ABTS reagents concentrations, pH, and incubation were established using 2k factorial designs. The proposed µPAD showed linearities upper than 0.99 in ranges 0.150–2.000 mg L−1 and 0.100–1.000 mg L−1 for FC and ABTS methods, respectively, detection limits were lower than 0.135 mg L−1, precision lower than 13.47 %, and recoveries between 82.27 % and 114.60 %. Ten different food samples were analyzed to demonstrate the applicability of the µPAD, and the results were compared with those obtained by the batch methods, showing no significant differences (p > 0.05). The µPAD in-situ sample treatment allowed removing interferences before the TPC and ABTS detection avoiding overestimation of the results. [ABSTRACT FROM AUTHOR]

• A simple and on-site paper-based analytical device for determine peroxide value. • Needing low amount of samples, solvents, and reagents and does not need glassware and skilled personnel. • A well-defined inverse logarithmic calibration curve is established between color intensity and PV. Peroxide value (PV) is one of the most typically used quality parameters to monitor lipid oxidation. Here, a simple paper-based analytical device (PAD) has been developed to determine PV in vegetable oils. The analysis is based on setting up the iodometric titration, where hydroperoxides in the oil are reacted with excess iodide ions to generate iodine molecules, on the paper substrate. The device is composed of two paper layers acting as reaction and detection zones, aligned in a metallic mold. A well-defined inverse logarithmic calibration curve was established between the measured PV by the official iodometric method (ISO;3960, 2017) and the color intensity of PAD. It offered a working range of 0.01–30.0 meq/Kg. The limit of detection of 0.015 meq/Kg demonstrated enough sensitivity of the method to estimate peroxide value in edible oils. On-site and visual detection, low cost, simplicity, and less solvent consumption are advantages of the proposed device. [ABSTRACT FROM AUTHOR]

We described a new paper-based device for performing flow injection analysis (FIA) in this article. A homemade three-electrode system, an origami paper strip, and a ceramic microheater were attached to a modular plastic supporting structure. Continuous flow in the origami paper strip was generated by the combination of capillary and the evaporation enhanced by a microheater. The proposed device was optimized and characterized by using K 4 Fe(CN) 6 /K 3 Fe(CN) 6 as a probe of chronoamperometry. Under optimal conditions, the device can perform a single analysis within 1 min and enable over 200 injections in one sequential test. To demonstrate its applicability, the device was utilized to detect uric acid in human serum and urine samples. The limit of detection was 1.1 μM and the linear range was from 0.01 mM to 1 mM. Moreover, the testing results of the real samples agreed with the reference values. The proposed method exhibits great promise for developing a convenient and high-performance FIA system on paper substrates. • A paper-based analytical device for flow injection analysis was developed based on locally enhanced evaporation. • The device combines the advantages of short analysis time and high injection capacity. • The device can perform a single analysis within 1 min and enable over 200 injections in one sequential test. • This device was successfully applied to detect uric acid in human serum and urine samples. [ABSTRACT FROM AUTHOR]

[Display omitted] • Products of urease catalyzes urea induce color change of Prussian blue nanoparticles. • A paper-based sensor depending on the Prussian blue pH sensitivity is developed. • Smartphone captures color signals of the sensor to achieve rapid detection of urea. Depending on the pH sensitivity of Prussian blue nanoparticles (PB NPs) and the specificity of urease-catalyzed urea, a paper-based colorimetric sensor was developed using urease, PB NPs, and cellulose filter paper. With the assistance of a smartphone, the rapid detection of urea can be realized. Under the optimal conditions, the linear range of the paper-based sensor for detection of urea is 0.5–5.0 mM, and the limit of detection is 0.27 mM. The RSD values of within-batch and between-batch repeatability are 2.5 % and 0.9 %, respectively. The method was successfully applied to the detection of urea in spiked milk samples and artificial urine sample, and the recoveries are in the range of 91.8–107.9%. The developed paper-based colorimetric sensor is a simple, economic, and rapid method that can be used for the determination of urea in real samples, particularly in resource-poor regions. [ABSTRACT FROM AUTHOR]

Electrochemical sensing technology integrated with a paper-based analytical device (PAD) offers an effective method for analyte detection. Nevertheless, it is still challenging to realize reliable and sensitive analysis owing to the basic shortcomings (inferior conductivity and high batch-to-batch variability) of paper-based working electrodes (WE) and lack of efficient signal amplification label. Herein, we proposed a novel electrochemical aptasensor to detect ochratoxin A (OTA), with MXene-Au as sensing substrates and Pt nanoparticles (NPs) anchored hollow structure NiCo-layered double hydroxides (Pt@NiCo-LDH) as signal amplification materials. The complementary DNA (cDNA) was firstly assembled onto the MXene-Au/WE via Au-S bonds. Then aptamer (apta)-binding Pt@NiCo-LDH with excellent peroxidase (POD)-like activity was immobilized through hybridization to trigger the "signal on" state, generating a significant electrochemical signal. The presence of OTA enabled the dissociation of the apta-cDNA hybrid, releasing signal amplification labels to achieve "signal off" state. Based on the "signal on/off" strategy, the aptasensor exhibited a wider linear range from 20 fg/mL to 100 ng/mL and a lower limit of detection of 8.9 fg/mL (S/N = 3). This work provided a new avenue for the versatile design of electrochemical paper-based platform that enabled the on-site detection of various analytes. [Display omitted] • Mxene-Au as sensing substrates exhibited high conductivity, good stability and low batch-to-batch variation. • Pt@NiCo-LDH showed excellent peroxidase-like catalytic activity and high durability to environmental conditions. • The electrochemical OTA aptasensor based on "signal on/off" strategy showed a wider linear and a lower limit of detection. • This work provided a new avenue for broad spectrum detection of analytes by simply altering the specific aptamer. [ABSTRACT FROM AUTHOR]

Pathogens are a persistent threat to human health, causing infectious disease and millions of deaths annually. The accurate and timely detection of pathogens is crucial in disease prevention, treatment, and monitoring. Although reliable detection methods are well established, many of them are still limited in use to clinical laboratories due to the need for costly and specialized instrumentation. In this study, we demonstrate a handheld and low-cost pathogen sensor consisting of a paper-based analytical device (μPAD) that can perform immunoassays and quantify analyte concentration by integrating with an automated color detection system that analyzes the color intensity of the μPAD. The core of the proposed sensor is the portable color detection system that can read the red-green-blue color of the paper emitted light from fluorescent nanomaterials, including graphene quantum dots (GQDs) and gold nanoclusters (AuNCs), which are conjugated with antibodies to indicate the immunoassay results, converting the presence of a pathogen to a colorful fluorescence signal. By adopting GQDs and AuNCs with high quantum yield and relatively high fluorescence intensity as the sensing signal, the paper-based detection system decreases the detection limit to as low as subnanogram/mL. Furthermore, GQDs and AuNCs can emit distinguishable fluorescence under the same light source (UV light) and possess limited background interference from the cellulose, enabling two or more analytes to be simultaneously detected with one UV light. Furthermore, a reaction time of just 10 min is needed, enabling diagnoses to be made in a timely manner and with high sensitivity. As a result, the proposed handheld pathogen sensor can rapidly detect the presence of pathogens with enhanced sensitivity and multiplexity, along with low instrumentation requirements, making it suitable for use in resource-limited settings where medical infrastructure is lacking. [Display omitted] • A handheld sensor consisting of a paper device and a color detection system was developed for on-site pathogen detection. • The system can read the color of the paper emitted light converting the presence of a pathogen into a fluorescence signal. • The high quantum yield GQDs and AuNCs help decrease the detection limit for multiple pathogens detection. [ABSTRACT FROM AUTHOR]

We developed a simple and low-cost cell culture monitoring system utilizing a paper-based analytical device (PAD) and a smartphone. The PAD simultaneously analyses glucose and lactate concentrations in the cell culture medium. Focusing on the fact that animal cells consume glucose and produce lactate under anaerobic conditions, oxidase- and horseradish peroxidase (HRP) enzyme-mediated colorimetric assays were integrated into the PAD. The PAD was designed to have three laminated layers. By using a double-sided adhesive tape as the middle layer and wax coating, a bifurcated fluidic channel was prepared to manipulate sample flow. At the inlet and the outlets of the channel, a sample drop zone and two detection zones for glucose and lactate, respectively, were positioned. When sample solution is loaded onto the drop zone, it flows to the detection zone through the hydrophilic fluidic channel via capillary force. Upon reaching the detection zone, the sample reacts with glucose and lactate oxidases (GOx and LOx) and HRP, immobilized on the detection zone along with colorless chromophores. By the Trinder’s reaction, the colorless chromophore is converted to a blue-colored product, generating concentration-dependent signal. With a gadget designed to aid the image acquisition, the PAD was positioned to the smartphone-embedded camera. Images of the detection zones were acquired using a mobile application and the color intensities were quantified as sensor signals. For the glucose assay using GOx/HRP format, we obtained the limit of detection (LOD ∼0.3 mM) and the limit of quantification (LOQ ∼0.9 mM) values in the dynamic detection range from 0.3 to 8.0 mM of glucose. For lactate assay using LOx/HRP, the LOD (0.02 mM) and the LOQ (0.06 mM) values were registered in the dynamic detection range from 0.02 to 0.50 mM of lactate. With the device, simultaneous analyses of glucose and lactate in cell culture media were conducted, exhibiting highly accurate and reproducible results. Based on the results, we propose that the optical sensing system developed is feasible for practical monitoring of animal cell culture. [ABSTRACT FROM AUTHOR]

[Display omitted] • An eco-friendly and sensitive method for nitrite determination was developed. • Application of a reliable Central composite design to optimize the process. • The simplified method was validated and comparable to the Griess method. • A rapid paper-based analytical device was applied for nitrite determination. A new eco-friendly, rapid, and sensitive spectrophotometric method was developed to determine small quantities of nitrite, based on a diazotization mechanism. In an acidic solution, sulfathiazole was first diazotized with sodium nitrite, followed by adding phosphate buffer to form a yellow-colored compound, which showed maximum absorption at 450 nm, without the need for the addition of coupling agents such as N-(1-naphthyl) ethylenediamine. The effects of reagents amount and the optimal experimental conditions were examined by Central composite design. The simplified method presented a wide linear range of nitrite between 0.091 μg mL−1 and 1.47 μg mL−1, a sensitivity of 0.447 Abs mL µg−1, a determination coefficient of 0.998, and a low limit of detection of 0.053 μg mL−1. The simplified method was found to be comparable to the Griess method. It was evaluated for the measurements of nitrite using the accuracy profile approach. The validation procedure results established that 80% of the future results would be within the acceptability limit of 10% over the validation domain ranging from 0.174 μg mL−1 to 1.37 μg mL−1. The developed method was furtherly applied in the determination of nitrite using a developed paper-based analytical device that detected a nitrite concentration of 3 μg mL−1 which is considered by the World Health Organization to be the maximal permissible limit of nitrite in drinking water. [ABSTRACT FROM AUTHOR]

• A novel chemiluminescence (CL) system was established for the determination of deltamethrin (DM). • The system is based on the enhancing effect of polyphosphate (PP) on graphene quantum dots (GQDs)-KMnO 4 CL reaction. • Two peaks were observed, at 490 and 695 nm as a characteristic emission for this unique CL system. • A simple paper-based analytical device (PADs) was used as platform for the analysis. A paper-based analytical device (PADs) combined with a powerful chemiluminescence (CL) system was established for the determination of deltamethrin (DM), based on the enhancing effect of polyphosphate (PP) on graphene quantum dots (GQDs)-KMnO 4 CL reaction. A possible mechanism for the obtained emission was proposed using the CL spectra, fluorescence and ultraviolet-visible patterns. The reaction of KMnO 4 and GQDs can lead to generation of GQDs in excited state (GQDs*), which can emit at 490 nm. Interestingly, PP changes the CL mechanism and the main emitter becomes Mn2+ instead of GQDs leading to a strong emission at 695 nm. Furthermore, the obtained multi-emission CL system was examined for analytical applications. The initial experiments showed that the amplified CL emission of the GQDs-KMnO4 system was selectively quenched in the presence of trace levels of DM, probably due to its effective interaction with GQDs or reaction with KMnO 4. This observation led to a facile, reliable and sensitive PADs-CL probe, developed for the determination of DM residue in food samples. Using this CL system and under the optimized experimental conditions, the generated signal is decreased by increasing DM concentration in the range of 0.3−10 μg mL-1 with limit of detection (LOD) of 0.15 μg mL-1. [ABSTRACT FROM AUTHOR]

A new design of a paper-based analytical device (PAD) for membraneless gas-separation with subsequent determination of iodate is presented. The rectangular PAD was invented as the folded pattern, where two circular reservoirs: the donor reservoir and the acceptor reservoir were situated in "a single paper" for convenient use. The hydrophobic barrier of each reservoir was easily fabricated by painting with a permanent marker. The PAD was demonstrated for the quantitative analysis of iodate, based on the fluorescence quenching of the bovine serum albumin-stabilized gold nanoclusters (BSA-AuNCs). The BSA-AuNCs were fast prepared by a microwave-assisted approach. The nanoclusters solution was applied into the acceptor reservoir, while the sample, iodide and sulfuric acid were sequentially aliquoted into the donor reservoir. After folding the PAD, the donor and the acceptor were mounted together via a two-sided mounting tape. The headspace between the two reservoirs allows membraneless gas-separation of free iodine from the donor to diffuse into the acceptor. Etching of gold core of the nanoclusters in the acceptor resulted in quenching of the red emission, was monitored by two methods, i.e. "fluorometric detection" (λ ex : 490 nm, λ em : 630 nm) and "image capture" of the acceptor under the UV irradiation by a smart phone's camera. Two calibrations were plotted accordingly to their detections and good linearities (r2 ˃ 0.98) were observed from 0.005 to 0.1 mmol L−1 iodate. High accuracy (mean recovery: 95.1 (±4.6) %) and high precision (RSD < 3%) were obtained. The lower limits of detection were 0.005 mmol L−1 (with fluorometric detection) and 0.01 mmol L−1 (with image capture). The method was effectively applied for the measurement of iodate in iodized salts and fish sauces without prior sample pre-treatment. Image 1 • A new design of a foldable paper-based analytical device (PAD) for membraneless gas-separation. • The foldable PAD composes of the donor and the acceptor reservoirs in the same paper for easy to use. • Highly sensitive detection of iodate based on fluorescence quenching of the gold nanoclusters. • Two detection methods on the PAD were viable: (i) fluorometric detection and (ii) image capture. • High accuracy (Mean recovery: 95.1 (+ 4.6) %) and high precision (RSD < 3 %). [ABSTRACT FROM AUTHOR]

Paraquat is a highly toxic herbicide. Paraquat poisoning is often fatal and is an important public health threat in many places. The quick identification and timely initiation of treatment based on timely analysis of the paraquat concentration in urine/serum could improve the prognosis for patients. However, current paraquat concentration measurements are time-consuming and difficult to implement due to the expensive and bulky equipment required. To address these practical challenges, paper-based devices have emerged as alternative diagnostic tools for improving point-of-care testing. In this study, we demonstrate the successful use of a paper-based analytical device for the accurate detection of urine paraquat concentration. The developed paper-based analytical device employs colorimetric paraquat concentration measurements. The R2 value for the urine paraquat standard curve was 0.9989, with a dynamic range of 0–100 ppm. The limit of detection was 3.01 ppm. Two other optical-based approaches, Spectrochip and NanoDrop, were used for comparison. The results suggest that the developed paper-based analytical device is comparable to other colorimetric measurements, as determined by Bland–Altman analysis. The device was clinically validated using urine from six paraquat-poisoned patients. The results prove that the developed paper-based analytical device is accurate, easy-to-use, and efficient for urine paraquat concentration measurement, and may enable physicians to improve clinical management. [ABSTRACT FROM AUTHOR]

• "Signal-on" electrochemical biosensor based on a competitive immunoassay was created. • The device pattern was designed to reduce the unnecessary processing and analysis time. • The amounts of OTC were successfully quantified in agricultural products. • This sensor provides high selectivity, sensitivity, portability, and low cost. In this work, we describe a new "signal-on" electrochemical biosensor based on a competitive immunoassay with a label-free format for the facile, sensitive and cost-effective determination of oxytetracycline (OTC). The device pattern was designed and printed on low-cost filter paper to construct a disposable paper-based analytical device (PAD) using a wax printing technique. The sensor consisted of a capture anti-OTC antibody (anti-OTC) and OTC-conjugated bovine serum albumin (OTC-BSA). Anti-OTC was first anchored onto the functionalized PAD, followed by the competitive binding of the OTC target and OTC-BSA. The amount of the captured OTC was examined by observing the signal response of the redox [Fe(CN) 6 ]3−/4−. In the presence of OTC, the current response was significantly increased with increasing OTC concentration, whereas the signal response was negligible in the absence thereof. The detected OTC concentration was linear over a range of 1−200 ng mL-1, and the corresponding values of 0.33 and 1.1 ng mL-1 were obtained for the limit of detection (LOD) and limit of quantitation (LOQ), respectively. This introduced sensor displayed high sensitivity and specificity, and the amounts of OTC were successfully quantified in agricultural products. This developed signal-on sensor may be an alternative tool for determining OTC residues and broader antibiotic targets. [ABSTRACT FROM AUTHOR]

A cheap/rapid technique for the fabrication of μPADs is presented for point of care analysis. Hydrophobic channels were formed across the width of the paper by spraying hot pure wax. This biocompatible novel process yielded uniform 300 ± 5 μm hydrophilic microchannels on paper, without the use of the cleanroom, UV lamp, or organic solvents and was completed in a single step without the need for a hotplate. Hot wax is properly impregnated across paper thickness by spraying under optimized temperature and pressure. Our method is advantageous in the cost and ease of fabrication, process time (<1 min), the feasibility of mass-fabrication, readout, environmental considerations and multiplexing due to the embossed structure of remnant wax. The performance of the resulting μPAD was assessed on a multiplexed Uric acid and Nitride assay, bearing 95% of confidence level in the readout against standardized tests. A novel RGB processing app was developed for smart-phones to quantify colorimetric read-outs through a heuristic normalization equation that converts RGB to integer systems. This combinatorial sensor demonstrates a good linear range (up to 800 μM for Uric acid and 1250 μM for Nitride), low detection limit (100 μM for uric acid and 156 μM for nitride). Image 1 • 300 μm hydrophilic microchannels are fabricated on paper by wax-spraying in single step. • Proper impregnation achieved by tuning of hot wax temperature and pressure. • Embossed wax channels are fabricated in 1 min, suitable for multiplexing. • Wax enabled μ PAD quantified uric-acid, nitrite & glucose by a combinatorial smart-phone App. [ABSTRACT FROM AUTHOR]

Rapid and accurate detection of nucleic acids plays a major role in biological research and clinical diagnostics. Here, a 3D multiple self-cleaning electrochemical ratiometric microfluidic paper-based analytical device (SER-μPAD) has been constructed for manganese super oxide dismutase (MnSOD) gene detection on the basis of the inner reference probe and exonuclease Ш (Exo Ш)-assisted analytes recycling amplification method. To simplify manual operations, a multipath self-cleaning tab that could manipulate fluid transport was introduced into the paper-based device, realizing time-programmable self-cleaning of the electrode. For achieving sensitive detection of MnSOD gene, the methylene blue (MB)-modified capture probe (CP) as the inner reference element was first self-assembled on triangular Au nanosheets modified paper working electrode to provide a built-in correction and improve the detection accuracy. When MnSOD gene existed, it hybridized with the hairpin-structured signal probe, triggering the cyclic amplification with the assistance of Exo Ш selective digestion to engender numerous residual DNA labeled with ferrocene (Fc) that could be captured on electrode surface by CPs. Hence, the Fc tags were close to the electrode surface, resulting in the oxidation peak current of Fc (I Fc) increase, while that of MB (I MB) was constant on account of the unchanged distance between the MB tags and the electrode. The value of I Fc / I MB was linear with MnSOD gene concentration from 10 nM to 1200 nM, and the detection limit was 3.91 nM. This strategy provides an accurate, robust, and sensitive method for nucleic acids detection and shows great potential in the construction of portable devices. • The T-AuNSs were successfully grown in situ on the cellulose fibers. • A multipath self-cleaning tab was designed to achieve self-cleaning process. • An inner reference probe was introduced to improve the reproducibility. • Exo Ш-aided analytes cyclic amplification greatly improved the sensitivity. • The device showed great potential in the construction of portable devices. [ABSTRACT FROM AUTHOR]