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Discrimination of nitroarenes with hydrophobic dyes in a polar (H 2 O) environment is difficult but possible via a lab-on-chip, with polymeric dyes immobilized on paper or nylon membranes. Here arrays of 12 hydrophobic poly(p -phenyleneethynylene)s (PPEs), are assembled into a chemical tongue to detect/discriminate nitroarenes in water. The changes in fluorescence image of the PPEs when interacting with solutions of the nitroarenes were recorded and converted into color difference maps, followed by cluster analysis methods. The variable selection method for both paper and nylon devices selects a handful of PPEs at different pH-values that discriminate nitroaromatics reliably. The paper-based chemical tongue could accurately discriminate all studied nitroarenes whereas the nylon-based devices represented distinguishable optical signature for picric acid and 2,4,6-trinitrotoluene (TNT) with high accuracy. [Display omitted] • Discrimination of nitroarenes was possible via a lab-on-chip, with dyes immobilized on paper or nylon membranes. • Hydrophobic poly (p -phenyleneethynylene)s (PPEs) were assembled into a chemical tongue. • Nylon-based devices distinguish picric acid and TNT with high accuracy. [ABSTRACT FROM AUTHOR]

Pancreatic hormones such as insulin play the crucial life-supporting role of glucose metabolism. Due to rapidly growing diabetic disorders and associated health complications globally, combined with the pathogenic viral infections severely affecting people with pre-existing conditions, new user-friendly, affordable molecular diagnostic approaches that offer simplicity, cost-effectiveness, and an ultra-sensitive detection in human biofluids are necessary to improve the global health. In this regard, a low-cost paper device that enables easy monitoring of fasting blood-relevant ultra-low picomolar insulin levels is innovative, giving broader applications to any other similar critical molecular targets. The essential contribution of this lab-on-paper is the combination of label-free electrochemical insulin aptasensing with a paper electrode device as a simpler, cheaper, and reliable molecular diagnostic approach for complex serum samples with supporting independent validation methods for confirming scientific rigor and fit-for-purpose of the presented approach. Our aptasensor features a carboxylated graphene-aptamer surface design offering a clinically relevant quantitative detection of picomolar insulin present in a 10-fold diluted neat serum based on interfacial capacitance changes in proportion to the serum insulin concentration (dynamic range 5–500 pM and limit of detection 1.5 pM). Application for undiluted serum samples is demonstrated. Furthermore, analysis of an actual diabetes patient serum sample and correlation of the capacitance sensor results with peroxidase antibody label-based insulin assay approaches are presented (amperometric detection and a commercial enzyme-linked immunosorbent assay are used as validation methods).

Tetracyclines (TCs) are the most common antibiotic drugs in the world. However, due to the overuse and difficulty of degradation, TCs pollution is becoming a global threat to aquatic and terrestrial biodiversity. Current methods for detecting TCs mainly rely on fluorescent probes or nanomaterials with enzyme-mimicking catalytic activities, which only provide a single signaling mode and are vulnerable to experimental factors. Herein, this study reports the development of an AND logic-gate-based sensing platform for TCs with fluorescent and colorimetric dual-signal readouts using Au@MnO 2 nanoparticles that could be mutually verified for the selective sensing of TCs. It was found that Au@MnO 2 nanoparticles could oxidize TC into its oxidation state (oxTC), resulting in significant green fluorescence emission. Meanwhile, the MnO 2 shell was etched away, and the released Au core nanoparticles gradually aggregated, with a color change from brown to light blue. As such, we established the fluorescence "turn-on" and colorimetric quantitative relationships towards TC with detection limits of 21.9 and 83.3 nM, respectively. Furthermore, Au@MnO 2 -based analytical paper devices were prepared and demonstrated successfully for the fluorescent and colorimetric dual-signal readout detection of TC in real samples. This paper sheds light on the on-site detection of tetracycline using paper-based analytical devices and smartphones. [Display omitted] • AND Logic-gate-based Au@MnO 2 sensing platform for tetracycline (TC) is developed. • Au@MnO 2 -based test paper was demonstrated for the visualization detection of TC. • Au@MnO 2 NPs can oxidize TC into green fluorescent oxTC in the fluorescence mode. • Au@MnO 2 NPs can be etched by TC with distinct color variance in colorimetric mode. • An explanation of the oxidation process of TC into oxTC by Au@MnO 2 is described. [ABSTRACT FROM AUTHOR]

Nitrite (NO 2 −) is a widely used food additive and long-term aging of cooked leftovers may also contribute to the formation of NO 2 −, excessive consumption of NO 2 − is harmful to human health. Developing an effective sensing strategy for on-site monitoring of NO 2 − has attracted considerable attention. Herein, a novel colorimetric and fluorometric probe ND-1 based on photoinduced electron transfer effect (PET) was designed for highly selective and sensitive detection of nitrite (NO 2 −) in foods. The probe ND-1 was strategically constructed by employing naphthalimide as the fluorophore and o -phenylendiamine as the specific recognition site for NO 2 −. The triazole derivative ND-1-NO 2 - could be produced exclusively by reacting with NO 2 −, leading to a visible colorimetric change from yellow to colorless accompanied by a significantly enhanced fluorescence intensity at 440 nm. The probe ND-1 exhibited promising sensing performances towards NO 2 − including high selectivity, rapid response time (within 7 min), low detection limit (47.15 nM) and wide quantitative detection range (0–35 μM). In addition, probe ND-1 was capable of quantitative detecting of NO 2 − in real food samples (including pickled vegetables and cured meat products) with satisfactory recovery rates (97.61%–103.08%). Moreover, the paper device loaded by probe ND-1 could be utilized for visual monitoring of NO 2 − levels variation of stir-fried greens. This study provided a feasible method for the accurate, traceable and rapid on-site monitoring NO 2 − in foods. [Display omitted] • A colorimetric and fluorometric probe was developed for detection of NO 2 −. • The probe was validated for analysis of natural NO 2 − in diverse food samples. • A paper-based device has been designed for visual quantitative detection of NO 2 −. • It provides a visual and convenient method for real-time monitoring the change of NO 2 − content in fried vegetables. [ABSTRACT FROM AUTHOR]

Regular monitoring of glucose and ketone contents in the body is vital for diabetic patients. Although estimation of the ketone content is necessary for proper healthcare monitoring, the research on the detection of ketone bodies is still nascent. Moreover, inaccurate eye-estimations and reliability are the key limitations of the widely used methodologies for estimating glucose in urine. Hence, simple procedures for fabricating reliable sensors are crucial for on-demand healthcare monitoring. Herein, we posit that a commercially available laser printer, without any added modifications, can be used to make paper-based sensors for colorimetric estimation of glucose and ketone in urine. We conducted a comprehensive experimental investigation to optimize the device designs for rapid estimation of the biomarkers. Also, for the first time, we present a detailed dynamic model of the flow-field in a variable cross-section paper device while considering the species transport and reaction kinetics within the porous media. Finally, we performed experiments with real urine samples to validate that our devices could detect results with zero false negatives. We believe that our present investigation and methodology can enable rapid and reliable fabrication of paper-based sensors for several fundamental studies and applications on affordable and non-invasive healthcare monitoring. [Display omitted] • A simple laser printer was used to make paper-based sensors for reliable estimation of glucose and ketone in urine. • A model was developed considering the variable channel area, the species transport and reaction kinetics in a paper device. • A desktop-based application was also developed for automatic estimation of the biomarkers in urine. • The methodology detected results with zero false negatives for complex real diseased samples. [ABSTRACT FROM AUTHOR]

A strategy to integrate capillary flow, electric field and Fenton reaction was developed to remove ionic dyes from water or concentrated NaCl solution for the first time. Tissue paper was used to construct capillary flow. The flow rates of water and crystal violet (CV) through it were measured, and then fitted with Lucas-Washburn model, Bosanquet model, and the fixed-bed adsorption model, respectively. Subsequently, an external electric field along the paper channels was introduced to prevent CV from flowing through the paper by electrostatic repulsion. Meanwhile, energy consumption of the integrated process was very low. For a concentrated NaCl (above 1 wt%) and dye solution, HClO formed by the electrolysis of Cl- ions further degraded CV. The relationship between voltage and NaCl concentration in the separation process was also investigated. Moreover, Fenton reaction was introduced to regenerate MnO 2 -coated paper and to enable the reutilization of the polluted device. Finally, removal of three ionic dyes (CV, methyl blue, and methylene blue) in water or 5 wt% NaCl solution were tested with a large paper device, in which the permeate was automatically collected by gravity. All the experiments showed 100% dye rejection with a water flow rate of 10–18 mL/h (at a cross-section area of 25 × 10−6 m2) and an energy consumption of 0.5–0.8 kwhm−3 to treat 100 ppm dye solution, and flow rate of 9–11 mL/h, energy consumption of 4.8–5.2 kwhm−3 to treat a solution of 100 ppm dye and 5 wt% NaCl. Overall, the results demonstrate the significant potentials of this new strategy for dye removal application. [Display omitted] • Dye separation via electrostatic repulsion through paper device driven by capillary flow. • Fitting flow velocities of water and dye by Bosanquet and adsorption-bed models. • Dye and dye/salt solution separation by electrostatic repulsion and electrolysis of Cl-. • Integration of Fenton reaction to regenerate MnO 2 -coated paper or increase water flux. • Flow rate of 10–18 mL/h, energy cost of 0.5–0.8 kwhm−3 to treat 100 ppm dye wastewater. [ABSTRACT FROM AUTHOR]

Wastewater-based surveillance of the COVID-19 pandemic holds great promise; however, a point-of-use detection method for SARS-CoV-2 in wastewater is lacking. Here, a portable paper device based on CRISPR/Cas12a and reverse-transcription loop-mediated isothermal amplification (RT-LAMP) with excellent sensitivity and specificity was developed for SARS-CoV-2 detection in wastewater. Three primer sets of RT-LAMP and guide RNAs (gRNAs) that could lead Cas12a to recognize target genes via base pairing were used to perform the high-fidelity RT-LAMP to detect the N, E, and S genes of SARS-CoV-2. Due to the trans-cleavage activity of CRISPR/Cas12a after high-fidelity amplicon recognition, carboxyfluorescein-ssDNA-Black Hole Quencher-1 and carboxyfluorescein-ssDNA-biotin probes were adopted to realize different visualization pathways via a fluorescence or lateral flow analysis, respectively. The reactions were integrated into a paper device for simultaneously detecting the N, E, and S genes with limits of detection (LODs) of 25, 310, and 10 copies/mL, respectively. The device achieved a semiquantitative analysis from 0 to 310 copies/mL due to the different LODs of the three genes. Blind experiments demonstrated that the device was suitable for wastewater analysis with 97.7% sensitivity and 82% semiquantitative accuracy. This is the first semiquantitative endpoint detection of SARS-CoV-2 in wastewater via different LODs, demonstrating a promising point-of-use method for wastewater-based surveillance.

Complex target SELEX always have been an intriguing approach to the scientific community, as it offers the potential discovery of novel biomarkers. We herein successfully performed SELEX on Bungarus caeruleus venom to develop a panel of highly affine aptamers that specifically recognizes the B. caeruleus (common krait) venom and was able to discriminate the B. caeruleus venom from Cobra, Russell's, and Saw-scaled viper's venom. The aptamers generated against the crude venom also lead to the identification of the specific component of the venom, which is β-Bungarotoxin, a toxin uniquely present in the B. caeruleus venom. The best performing aptamer candidates were used as a molecular recognition element in a paper-based device and were able to detect as low as 2 ng krait venom in human serum background. The developed aptamer-based paper device can be used for potential point-of-care venom detection applications due to its simplicity and affordability. [ABSTRACT FROM AUTHOR]