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An advanced sensing platform for the on-site and real-time monitoring of cyanide (CN−) pollution was developed, addressing the key challenges of enhancing the selectivity and sensitivity, whilst simplifying the sensing process. This platform features a novel colorimetric sensor (PDA-BMN) created by incorporating a receptor for CN− recognition within a polydiacetylene (PDA) conjugated polymer system. The interaction of CN− with the receptor distorted the π-conjugated backbone, causing a distinct color change from blue to orange, with a limit of detection (LOD) of 0.55 µM, thereby highlighting its high sensitivity. The PDA-BMN system was integrated into a lateral flow assay (LFA) strip to facilitate on-site monitoring. The LFA strip was strategically designed with a partially pressed zone to reduce the fluid flow rate, enhance the reaction time, and increase the probability of interaction with the PDA-BMN sensor. This innovation resulted in a significant colorimetric transition, enabling the rapid and sensitive detection of CN− without the requirement for analytical instruments. This study demonstrates the effectiveness of combining PDA and LFA systems for real-time environmental monitoring, offering a robust, efficient, and user-friendly solution for detecting CN− pollution. [Display omitted] • A PDA-BMN colorimetric sensor was developed for the detection of CN–. • Interactions between CN− and the receptor distorted the π-conjugated backbone. • This sensor was sensitive (LOD = 0.66 μM), giving a blue-to-orange color change. • The PDA-BMN system was integrated into an LFA strip to facilitate on-site monitoring. • Pressing this strip reduced the fluid flow rate, enhancing the detection performance. [ABSTRACT FROM AUTHOR]

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).

Paper-based analytical devices possess desirable properties such as low cost, convenient production, and rapid output. These advantages over conventional analytical devices have attracted tremendous attention in recent years, and an abundance of fabrication techniques have been achieved with different designs. Related approaches are adopted by scientists and engineers from different research fields to create practical devices tailored for various applications. Among a diverse selection of strategies, paper-based analytical devices featuring enclosed channels can protect its contents from environmental harm, which is helpful in designing paper-based devices aimed toward practical use. However, superior properties of enclosed device designs have often been neglected when a paper-based platform is selected, and related discussion is still lacking in the field. To fill this empty space in the relevant literature, important issues are highlighted and recent research achievements are included in this article, which should have implication for scientists interested in sensing technology, analytical chemistry, material science, and miniaturized devices. For the convenience of reader's understanding, this article provides a general introduction to the basic properties and concepts of paper-based analytical devices. Firstly, commonly used fabrication strategies and detection methods are mentioned, with an in-depth emphasis on paper-based devices with enclosed channels, including breakthroughs in device types, thoughts on novel fabrication, and practical application examples. Subsequently, other important topics related to enclosed paper-based device design are summarized, and future challenges and opportunities in the field are also discussed. Image 1 • Brief introduction to the background of paper-based analytical devices. • In-depth discussion of paper-based analytical devices with enclosed channels. • How enclosed channels improve device lifetime and flow properties. • Challenges and perspective opportunities for enclosed paper-based devices. [ABSTRACT FROM AUTHOR]

Background: Paper-analytical devices (PADs) have gained popularity as a simple and low-cost alternative for determining a wide range of analytes including proteins. Even though several colorimetric PADs methods for protein estimation are reported in literature, they lack justification for the chosen method and parameters therein. Aim: Major aim of this work was to thoroughly evaluate the most commonly used colorimetric protein assays and recommend the most appropriate method for PADs platform. Method: We performed following six colorimetric protein assays on PADs: biuret, lowry, bicinchoninic acid, bradford, bromocresol green, and tetrabromophenol blue. We obtained assay signal by analyzing images of the PADs and then assessed analytical figures of merit. Result: Precision, accuracy, LOD, and LOQ of PADs protein assay methods ranged from 1.2 to 6.4%, 73.3–102.4%, 0.3–3.8 ​mg/mL, and 1.2–12.8 ​mg/mL, respectively. Out of six methods, we determined bromocresol green and tetrabromophenol blue as the best methods for serum and urine samples, respectively based on their optimized parameters and analytical figures of merit. The total average serum and urine protein in human samples were found to be 94.6 ​± ​16.2 ​mg/mL and 2.1 ​± ​1.5 ​mg/mL, respectively using PADs methods. The PADs result on human samples moderately correlated with the results from spectrophotometric determination (r2 ​> ​0.6). Conclusion: Paper-based protein assays were easy to perform and were completed with thousand-fold less volume of samples/reagents without a spectrophotometer compared to conventional assay methods. After testing human samples, we found one protein assay method may not be appropriate for all types of samples.

Paper based assays are paving the way to automated, simplified, robust and cost-effective point of care testing (POCT). We propose a method for fabricating three dimensional (3D) microfluidic paper based analytical devices (μPADs) via combining thin adhesive films and paper folding, which avoids the use of cellulose powders and the complex folding sequence and simultaneously permits assays in several layers. To demonstrate the effectiveness of this approach, a 3DμPADs was designed to conduct more assays on a small footprint, allowing dual colorimetric and electrochemical detections. More importantly, we further developed a 3D platform for implementing automated and multiplexed ELISA in parallel, since ELISA, a routine and standard laboratory method, has rarely been used in practical analyses outside of the laboratory. In this configuration, complex and multistep diagnostic assays can be carried out with the addition of the sample and buffer in a simple fashion. Using Troponin I as model, the device showed a broad dynamic range of detection with a detection limit of 0.35 ng/mL. Thus, the developed platforms allow for various assays to be cost-effectively carried out on a single 3D device, showing great potential in an academic setting and point of care testing under resource-poor conditions. fx1 • Based on thin adhesive films and paper folding, 3D paper devices were assembled. • A paper device was developed to allow dual colorimetric and electrochemical detection. • A 3D platform was developed for implementing automated and multiplexed ELISA in parallel. [ABSTRACT FROM AUTHOR]

Abstract Paper based biosensor devices have the benefit of easy-use, low-cost and environmental friendly for point-of-care diagnostic application. In this research, we report a novel form of paper based biosensor with hierarchical assembled nanomaterials and MOF enhanced bio-probes for the simultaneous detection of microRNA-141 (miR-141) and microRNA-21 (miR-21) which have the potential for early cancer detection. The combination of multi-dimensional nanomaterial allows low impedance and high sensing area on typical poorly defined paper substrate. MOF conjugated bio-probe, methylene blue (MB) and ferrocene (Fc) with distinguishable electrochemical signal, further contributed to the high selectivity and sensitivity. Simultaneously detection of miR-141 and miR-21 with a detection limit of 0.1 fM was demonstrated under optimal conditions. All these features enable accurately target detection in serum samples. Therefore, this strategy is of promising as an inexpensive, easy access diagnosis platform for cancers by means of simultaneously detection of a variety of miRNA biomarkers. Highlights • MoS 2 /AuNPs/AgNW paper-based electrode was used as sensing platform. • Hairpin DNA nanostructures-based biosensor was developed with the detection limit of 0.1 fM. • PtCuMOFs/DNA was used for simultaneous detection miRNA and signal amplification. • The DNA biosensor could be utilized in real serum sample analysis. [ABSTRACT FROM AUTHOR]

In this work, a paper device consisted of a patterned paper chip, wicking pads, and a base was fabricated. On the paper chip, DNA–gold nanoparticles (DNA–AuNPs) were deposited and Hg2+ ions could be adsorbed by the DNA–AuNPs. The formed DNA–AuNP/Hg2+ nanozyme could catalyze the tetramethylbenzidine (TMB)–H2O2 chromogenic reaction. Due to the wicking pads, a larger volume of Hg2+ sample could be applied to the paper device for Hg2+ detection and therefore the color response could be enhanced. The paper device achieved a cut-off value of 50 nM by the naked eye for Hg2+ under optimized conditions. Moreover, quantitative measurements could be implemented by using a desktop scanner and extracting grayscale values. A linear range of 50–2000 nM Hg2+ was obtained with a detection limit of 10 nM. In addition, the paper device could be applied in the detection of environmental water samples with high recoveries ranging from 85.7% to 105.6%. The paper-device-based colorimetric detection was low-cost, simple, and demonstrated high potential in real-sample applications.

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]

L’articolo esamina l’evoluzione dei pop-up books destinati all’infanzia, nel periodo compreso tra la fine del Settecento e la fine del Novecento e, in particolare, la personalità artistica di alcuni editori/paper engineer (Dean and Son, Lothar Meggendorfer, Ernest Nister, S. Louise Giraud, Vojtĕch Kubăsta). Il contributo illustra inoltre il funzionamento di alcuni dispositivi cartotecnici da loro progettati e realizzati. Resta deliberatamente escluso dall’indagine il pop-up book digitale, che presenta caratteristiche e problematiche diverse rispetto al libro cartaceo e che pertanto esulano dall’ambito di interesse del saggio.

Abstract: In the present study, we aimed to determine the applicability of a paper container for the vitrification of in vitro matured (IVM) bovine oocytes. In experiment 1, IVM oocytes were exposed to vitrification solution (20% dimethylsulfoxide (DMSO), 20% ethylene glycol (EG), and 5 mol/L sucrose), using a two‐step method, for 30 s; loaded onto either a paper container or Cryotop; and stored in liquid nitrogen. No significant difference (P < 0.05) in the survival and blastocyst formation rates after in vitro vitrification was observed between the paper container and Cryotop. In experiment 2, IVM oocytes were exposed to either a two‐ or three‐step vitrification solution. The three‐step vitrification solution was not significantly different from the two‐step solution in terms of oocyte survival, cleavage and blastocyst rates. In experiment 3, in vitro produced blastocysts were graded according to the manual of the International Embryo Transfer Society (grades 1 and 2) and vitrified using the two‐ and three‐step methods. For grade 2 blastocysts, the three‐step method showed significantly higher (P < 0.05) survival and hatched blastocyst rates than the two‐step method, whereas for grade 1 blastocysts, no significant difference was observed. In conclusion, the paper device and three‐step technique are suitable for oocytes and embryo vitrification. [ABSTRACT FROM AUTHOR]

Telomerase is extensively expressed in various cancer cells and recognized as a target for cancer drug discovery. In the present study, a simple and amplification-free fluorescence assay based on polyamidoamine starburst dendrimer (PAMAM dendrimer)-activated paper device is proposed for sensitive detection of telomerase activity through hybridization of Cy5 modified single strand DNA probes with telomerase extension products. The paper substrate is fabricated by hand drawing according to a template, which is low cost, instrument free and easy operation. PAMAM is rich in amino groups on its surface and employed to immobilize the telomerase substrate (TS) primer. Highly sensitive detection of telomerase activity in HeLa cell lysate of 10 cells is achieved since the PAMAM dendrimer-activated paper surface can provide high density of binding sites for immobilization of TS primer. The experimental results also demonstrate that the assay can be employed to evaluate telomerase activity levels of various cell lines and screen telomerase inhibitors. [ABSTRACT FROM AUTHOR]

Paper-based analytical devices are an emerging class of lightweight and simple-to-use analytical platform. However, challenges such as instrumental requirements and chemical reagents durability, represent a barrier for less-developed countries andmarkets. Herein, we report an advanced laminated device using red emitting copper nanocluster and RGB digital analysis for signal improvement. Upon RGB system assistance, the device signal-to-background ratio and the calibration sensitivity are highly enhanced under a filter-free setup. In addition, the calibration sensitivity, limit of detection, and coefficient of determination are on par with those determined by instrumental fluorescence analysis. Moreover, the limitation of using oxidation-susceptible fluorescent nanomaterials is overcome by the introduction of protecting tape barriers, antioxidative sheets, and lamination enclosing. The robustness of device is highly advanced, and the durability is prolonged to more than tenfold. [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]

The authors describe a semi-quantitative colorimetric method for visual detection of organophosphorus pesticides (OPs). It is based on the aspect ratio dependent absorbance of gold nanorods (AuNRs) which is due to the localized surface plasmon resonance. The aspect ratio can be tailored by the Au(III) complex formed with cetyltrimethylammonium bromide (CTAB) which is affected by acetylcholinesterase (AChE) based hydrolysis. OPs act as inhibitors of this reaction. In the absence of OPs, the product (thiocholine) of enzymatic hydrolysis consumes almost all the Au(III) species. In this case, the amount of residual Au(III)-CTAB complexes is small, and etching of the AuNRs does not occur. In the presence of OPs, however, the activity of AChE is inhibited. Hence, only small quantities of (or no) thiocholine is produced, and Au(III) is not consumed. Au(III) is capable of etching AuNRs and to change their aspect ratio. This leads to a color change from brownish to gray, cyan, green, blue, purple, red, and colorless that can be easily observed with bare eyes. The AuNRs were incorporated into cellulose paper to obtain a paper stripe for visual detection of OPs. Under optimal conditions, both methods (AuNRs in aqueous solutions and on paper) allowed various OPs to be determined. Applied to parathion, the method had a detection limit as low as 1.2 ppb and a linear range from 0.01 to 1.84 ppm. It was applied to the analysis of cabbage washing solutions and sea water samples, and acceptable accuracy and good resolution were found. In our preconception, the method represents a valuable tool for on-site detection of OPs in agriculture products and food. [ABSTRACT FROM AUTHOR]

A simple and sensitive colorimetric method is developed for organophosphrous pesticides (OPs) analysis based on the enzymatic hydrolysis reaction of acetylcholinesterase and the dissolution of gold nanoparticles (AuNPs) in Au 3+ -cetyltrimethylammonium bromide (Au 3+ -CTAB) solution. In the absence of OPs, the enzymatic hydrolysis product, thiocholine, would reduce Au 3+ and protect the AuNPs from dissolution by the Au 3+ -CTAB. In the presence of OPs, however, the activity of AChE is inhibited, which could not or could only produce a small amount of thiocholine to consume the Au 3+ . In this case, the large amount of residual Au 3+ dissolves the AuNPs and decreases both the concentration and size of the AuNPs, thus leading to an obvious red-to-light pink or red-to-colorless color change. Under optimal conditions, the colorimetric method could indicate the presence of OPs, with the concentration down to 0.7 ppb. After loading AuNPs on a cellulose paper, an AuNPs-coated dipstick is developed for the detection of OPs, which is highly sensitive with an observable limit of detection of 35 ppb. Practical sample analyses in tap water, apple washing solution, and sea water indicate the colorimetric method has acceptable accuracy and good stability, even in the system containing 5 M of NaCl. Regarding these merits, the as-proposed method could be applied for the point-of-care analysis of OPs in complex systems. [ABSTRACT FROM AUTHOR]

Paper-based analytical devices are an emerging class of lightweight and simple-to-use analytical platform. However, challenges such as instrumental requirements and chemical reagents durability, represent a barrier for less-developed countries and markets. Herein, we report an advanced laminated device using red emitting copper nanocluster and RGB digital analysis for signal improvement. Upon RGB system assistance, the device signal-to-background ratio and the calibration sensitivity are highly enhanced under a filter-free setup. In addition, the calibration sensitivity, limit of detection, and coefficient of determination are on par with those determined by instrumental fluorescence analysis. Moreover, the limitation of using oxidation-susceptible fluorescent nanomaterials is overcome by the introduction of protecting tape barriers, antioxidative sheets, and lamination enclosing. The robustness of device is highly advanced, and the durability is prolonged to more than tenfold.

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]

Loop-mediated isothermal amplification (LAMP) has been widely used for detecting pathogens. However, power-free and clear visualization of results still remain challenging. In this study, we developed a paper device integrated with power-free DNA detection strategy realized by polydopamine aggregation. In the presence of DNA amplicons, the polymerization of dopamine into aggregated polydopamine was hindered, while in the absence of DNA amplicons, polydopamine aggregation is facilitated. The porosity of the paper enabled the capillary flow of dispersed polydopamine for positive sample, while aggregated polydopamine remained at the bottom of the paper strip due to large size of the aggregates for negative sample. Based on this mechanism, we fabricated a slidable paper device integrating LAMP with dopamine polymerization for the naked-eye detection, operated in a seamless manner. Moreover, the introduced paper device was successfully used to detect DNA extracted from Escherichia coli O157:H7 and SARS-CoV-2 within 25 min, as well as Enterococcus faecium within 35 min. The detection limits of both Escherichia coli O157:H7 and SARS-CoV-2 were 10−4 ng/μL. The introduced paper device can be used as a simple and sensitive tool for detecting multiple infectious pathogens, making it an ideal tool particularly for resource-limited environment. • Polydopamine aggregation-based readout of LAMP amplicons was developed for multiplex pathogen detection. • LAMP and dopamine-based detection was performed using a paper device. • The paper device could detect E. coli O157:H7, E. faecium, and SARS-CoV-2. • LOD of the paper device was as low as 10 − 4 ng/μL of DNA template. [ABSTRACT FROM AUTHOR]

• Low-cost paper device was fabricated for fast screening of tetracycline in milk. • The desirable porous structure of the device strengthened the detection signal. • Large quantity of 20 types of commercial milks was tested to validate the method. • The method can be used for continuously monitoring TC's dynamic degradation. A low-cost and portable paper-based analytical device has been developed for high throughput and on-site monitoring TC residue in milk through visualized colorimetric reaction. The filtration and concentration effect induced by the porous nature of paper contribute to strengthen the color intensity, leading to quantitative and sensitive detection of tetracycline reaching 1 ppm detection limit, with the linear range of 1–100 ppm both in water and milk samples. The applicability was demonstrated by detection of TC in 18 different types of real milk samples with good recovery ranging from 88% to 113%. Furthermore, the dynamic degradation behavior of tetracycline was monitored through the device. To the best of our knowledge, this is the first report of colorimetric detection of tetracycline in milk using the paper-based device. This simple, fast, cost-effective (~$0.50 per device) and equipment-free paper-based platform provides a promising tool for future application in food and environmental safety. [ABSTRACT FROM AUTHOR]

In this work, a paper device consisted of a patterned paper chip, wicking pads, and a base was fabricated. On the paper chip, DNA–gold nanoparticles (DNA–AuNPs) were deposited and Hg2+ ions could be adsorbed by the DNA–AuNPs. The formed DNA–AuNP/Hg2+ nanozyme could catalyze the tetramethylbenzidine (TMB)–H2O2 chromogenic reaction. Due to the wicking pads, a larger volume of Hg2+ sample could be applied to the paper device for Hg2+ detection and therefore the color response could be enhanced. The paper device achieved a cut-off value of 50 nM by the naked eye for Hg2+ under optimized conditions. Moreover, quantitative measurements could be implemented by using a desktop scanner and extracting grayscale values. A linear range of 50–2000 nM Hg2+ was obtained with a detection limit of 10 nM. In addition, the paper device could be applied in the detection of environmental water samples with high recoveries ranging from 85.7% to 105.6%. The paper-device-based colorimetric detection was low-cost, simple, and demonstrated high potential in real-sample applications. [ABSTRACT FROM AUTHOR]

In this work, a self-circulation oxygen-hydrogen peroxide-oxygen (O 2 -H 2 O 2 -O 2 ) system with photogenerated electrons as fuel and highly active hemin monomers as operators was engineered for ultrasensitive cathode photoelectrochemical bioassay of microRNA-141 (miRNA-141) using a stacked sealed paper device. During the circulation, the photogenerated electrons from BiVO 4 /Cu 2 O photosensitive structures assembled on a reduced graphene oxide paper electrode first reduced the electron acceptors (dissolved O 2 ) to H 2 O 2 , which was then catalytically decomposed by hemin monomers to generate O 2 again. The regenerated O 2 continued to be reduced, which made O 2 and H 2 O 2 stuck in the infinite loop of O 2 -H 2 O 2 -O 2 accompanied by the fast consumption of photogenerated electrons, generating an amplified photocurrent signal. When a target existed, a duplex-specific nuclease-induced target recycling reaction with dual trigger DNA probes as the output was performed to initiate the assembly of bridge-like DNA nanostructures, which endowed the self-circulation system with dual destruction functions as follows. (i) Reduced fuel supply: the assembled DNA bridges acting as a negatively charged barrier prevented the photogenerated electrons from participating in the O 2 reduction to H 2 O 2 . (ii) Incapacitation of operators: DNA bridging induced the dimerization of hemin monomers linked on the DNA hairpins to catalytically inactive hemin dimers, leading to the abortive regeneration of O 2 . These destruction functions resulted in the circulation interruption and a remarkably decreased photocurrent signal. Thus, the developed cathode photoelectrochemical biosensing platform achieved ultrasensitive miRNA-141 detection with a linear range of 0.25 fM to 1 nM and a detection limit of 83 aM, and it also exhibited high accuracy, selectivity, and practicability.

The pyrophosphate ion (P 2 O 7 4- , PPi) plays a critical role in various biological processes and acts as an essential indicator for physiological mechanism investigations and disease control monitoring. However, most of the currently available approaches for PPi species detection for practical usage still lack appropriate indicator generation, straightforward detection requirements, and operation convenience. In this study, a highly sensitive and selective PPi detection approach via the use of nanozymatic carbon dots (CDs) is introduced. This strategy eliminates the common need for metal ions in the detection process, where a direct indicator-PPi interaction is adopted to provide straightforward signal reports, and importantly, through a green indicator preparation. The preparation of this nanozymatic CDs' indicator utilizes an aqueous solution refluxing, employing galactose and histidine as the precursor materials. The mild conditions of the solution refluxing produce fluorescent CDs exhibiting peroxidase-mimic properties, which can catalyze the o -phenylenediamine oxidation under the presence of H 2 O 2 . The introduction of PPi species, interestingly, inhibits this process very efficiently, the extent of which can be colorimetrically monitored by the generated yellow product 2,3-diaminophenazine. Spectroscopic results point to CD surface functional groups' selective binding toward PPi species, which severely interferes with the electron transfer process in the enzymatic catalysis. Relying on this CD peroxidase-mimetic property inhibition, sensitive and selective recognition of PPi reaches a detection limit of 4.29 nM, enabling practical usage in complex matrixes. Owing to the superior compatibility and high stability of nanozymatic CDs, they can also be inkjet-printed on paper-based devices to create a portable and convenient platform for PPi detection. Both the solution and the paper-device-based selective recognitions confirm this unique and robust metal-free inhibitive PPi detection, which is supported by a convenient green preparation of nanozymatic CDs.

Background: Paper-analytical devices (PADs) have gained popularity as a simple and low-cost alternative for determining a wide range of analytes including proteins. Even though several colorimetric PADs methods for protein estimation are reported in literature, they lack justification for the chosen method and parameters therein., Aim: Major aim of this work was to thoroughly evaluate the most commonly used colorimetric protein assays and recommend the most appropriate method for PADs platform., Method: We performed following six colorimetric protein assays on PADs: biuret, lowry, bicinchoninic acid, bradford, bromocresol green, and tetrabromophenol blue. We obtained assay signal by analyzing images of the PADs and then assessed analytical figures of merit., Result: Precision, accuracy, LOD, and LOQ of PADs protein assay methods ranged from 1.2 to 6.4%, 73.3-102.4%, 0.3-3.8 ​mg/mL, and 1.2-12.8 ​mg/mL, respectively. Out of six methods, we determined bromocresol green and tetrabromophenol blue as the best methods for serum and urine samples, respectively based on their optimized parameters and analytical figures of merit. The total average serum and urine protein in human samples were found to be 94.6 ​± ​16.2 ​mg/mL and 2.1 ​± ​1.5 ​mg/mL, respectively using PADs methods. The PADs result on human samples moderately correlated with the results from spectrophotometric determination (r 2  ​> ​0.6)., Conclusion: Paper-based protein assays were easy to perform and were completed with thousand-fold less volume of samples/reagents without a spectrophotometer compared to conventional assay methods. After testing human samples, we found one protein assay method may not be appropriate for all types of samples., Competing Interests: There are no conflicts to declare., (© 2020 The Authors.)

This work describes the preparation of bimetallic Cu-Pd nanoparticles (NPs) on supports like reduced graphene oxide (rGO), graphitic carbon nitride (g-C3N4) and MoS2 sheets with a size of <10 nm. rGO is found to be the best support for synthesizing Cu-Pd NPs with controlled shape, size and oxidation state. The Cu-Pd/rGO nanocomposite also demonstrated the best peroxidase and oxidase mimicking activity compared to Cu-Pd/g-C3N4 and Cu-Pd/MoS2 nanocomposites. The peroxidase mimicking activity of Cu-Pd/rGO was investigated in more detail, and a glucose oxidase (GOx) based glucose sensor was constructed that is based on the enzymatic formation of H2O2 and the Cu-Pd NPs-assisted oxidation of tetramethylbenzidine by H2O2 to give a blue-green coloration with absorption maxima at 652 nm. The assay has a 0.29 μM detection limit and a detection range that extends from 0.2 to 50 μM. The method was applied to the determination of glucose in diluted serum samples, and results compared well to those acquired with a clinical analyzer. The method also was applied in a colorimetric paper-based test stripe that can detect glucose within 10 min.Schematic representation of a sensitive colorimetric glucose assay based on bimetallic Cu-Pd nanoparticles supported on 2D nanosheets, and construction of a paper based device for rapid glucose detection. [ABSTRACT FROM AUTHOR]

This work describes the preparation of bimetallic Cu-Pd nanoparticles (NPs) on supports like reduced graphene oxide (rGO), graphitic carbon nitride (g-C 3 N 4 ) and MoS 2 sheets with a size of <10 nm. rGO is found to be the best support for synthesizing Cu-Pd NPs with controlled shape, size and oxidation state. The Cu-Pd/rGO nanocomposite also demonstrated the best peroxidase and oxidase mimicking activity compared to Cu-Pd/g-C 3 N 4 and Cu-Pd/MoS 2 nanocomposites. The peroxidase mimicking activity of Cu-Pd/rGO was investigated in more detail, and a glucose oxidase (GOx) based glucose sensor was constructed that is based on the enzymatic formation of H 2 O 2 and the Cu-Pd NPs-assisted oxidation of tetramethylbenzidine by H 2 O 2 to give a blue-green coloration with absorption maxima at 652 nm. The assay has a 0.29 μM detection limit and a detection range that extends from 0.2 to 50 μM. The method was applied to the determination of glucose in diluted serum samples, and results compared well to those acquired with a clinical analyzer. The method also was applied in a colorimetric paper-based test stripe that can detect glucose within 10 min. Graphical abstract Schematic representation of a sensitive colorimetric glucose assay based on bimetallic Cu-Pd nanoparticles supported on 2D nanosheets, and construction of a paper based device for rapid glucose detection.

This paper presents a whole-cell biosensor that operates in conjunction with a smartphone-based fluorescence diagnostic system on a paper device to monitor the concentration of gold ions in human urine. The heavy metal-tolerant bacteria Cupriavidus metallidurans was genetically engineered for use as a chassis in a red fluorescent protein (RFP)-based microbial sensor. The biosensor is highly sensitive to gold ions, with a detection limit of 110 nM. The proposed smartphone-based analysis system provides a user-friendly approach to design tools of personal health monitoring for reporting the presence of gold ions in human urine.

Flexible electronics will form the basis of many next-generation technologies, such as wearable devices, biomedical sensors, the Internet of things, and more. However, most flexible devices can bear strains of less than 300% as a result of stretching. In this work, we demonstrate a simple and low-cost paper-based photodetector array featuring superior deformability using printable ZnO nanowires, carbon electrodes, and origami-based techniques. With a folded Miura structure, the paper photodetector array can be oriented in four different directions via tessellated parallelograms to provide the device with excellent omnidirectional light harvesting capabilities. Additionally, we demonstrate that the device can be repeatedly stretched (up to 1000% strain), bent (bending angle ±30°), and twisted (up to 360°) without degrading performance as a result of the paper folding technique, which enables the ZnO nanowire layers to remain rigid even as the device is deformed. The origami-based strategy described herein suggests avenues for the development of next-generation deformable optoelectronic applications.

Organic layered materials have intercalation and dynamic properties. The dynamic properties are tuned by the intercalation of the guests. In general, however, it is not easy to achieve the homogeneous and thin coating of the layered materials on substrates with complex shapes because of the two-dimensional anisotropic structures. In the present work, the layered organic composites were homogeneously coated on a variety of substrates for application to practical devices. The metal-ion-intercalated layered polydiacetylene (PDA-M n+ ) with tunable stimuli-responsive color-change properties was coated on substrates, such as paper and cotton consisting of cellulose fibers. The homogeneous and thin coating of the precursor monomer crystal was achieved on the substrates through the controlled crystal growth. The intercalation and topochemical polymerization generated PDA-M n+ on the substrates. The PDA-M n+ -coated devices visualized temperature distribution of two-dimensional surface and three-dimensional space in real time.