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We present a colorimetric probe based on polyvinylpyrrolidone-capped gold nanoparticles (PVP-AuNPs) that is sensitive and selective for cysteine (Cys). A microfluidic paper-based analytical device (μ-PAD) with embedded dried PVP-AuNPs at the polyethersulfone (PES) paper surface is used for Cys detection. When thiol molecules attach to PVP-AuNPs in the presence of Cys, they clump together, and this causes the solution's color to shift from red to blue within 5 minutes. The device is capable of detecting Cys levels between 1.0 μM and 50.0 μM with a limit of detection (LOD) of 0.2 μM under optimized conditions. The stability of the μ-PAD was tested for 100 days, demonstrating re-dispersibility to detect Cys levels in blood. Dried PVP-AuNP-μPADs were integrated with blood plasma separation modules for point-of-care (POC) Cys detection. Consequently, the device shows potential as a self-sustaining, quantification platform with a recovery percentage ranging from 98.44 to 111.9 in clinical samples.

Hydrogen Peroxide (H 2 O 2 ) is a highly hazardous, toxic, and carcinogenic chemical compound utilised in various industries-based applications. Despite strict restriction, they are deliberately added to food items such as milk as preservatives to increase its shelf life. Herein, we have formulated a green rapid colorimetric nanosensor for detection of H 2 O 2 in milk using cotton leaves as both reducing and functionalizing agent for synthesis of silver nanoparticles (AgNPs). UV-Vis spectra exhibit a strong plasmonic peak at around 434 nm. X-Ray Diffraction (XRD) analysis was performed to determine the crystallinity of the nanoparticles. Field Emission Scanning Electron Microscope (FESEM) and Transmission Electron Microscope (TEM) characterizations revealed spherical morphology with size approximately ∼16 nm. This functionalized nanoparticle could colorimetrically sense presence of H 2 O 2 in milk samples both in liquid media and on paper substrates with Limit of Detection (LOD) of 8.46 ppm even in presence of other interfering substances in milk. This inexpensive route will pave the way for in depth research., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

We proposed a triple functional SERS substrate by immobilized Ag nanoparticles on the surface of filter paper. The high dense Ag nanoparticles were distributed on the SERS substrate via in-situ growth process. By optimizing the parameter in preparation process, the optimal filter paper SERS substrate was fabricated by using 30 mM of AgNO 3 with 20 S growth time. Due to capillary-effect wicking of cellulose fiber, the paper SERS substrate provide simple, fast and pump-free function for transferring analyte onto sharp tip through development of fluid. The fluid flow also brings target concentrate effect within the tip area. Furthermore, the separation feasibility was obtained during the development process of fluid. The preconcentrated effects not only enhanced the SERS signal of analyte, but also improve the fluorescence visible effect. The filter paper SERS substrate was successfully used for separating, concentrating and detecting Sudan dye from chili product, the detection limit could achieve 10 -6 M. This study developed a portable, cost-effective and eco-friendly SERS substrate for separating and detecting trace chemical in food., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

The exploration into nanomaterial-based nonenzymatic biosensors with superb performance in terms of good sensitivity and anti-interference ability in disease marker monitoring has always attained undoubted priority in sensing systems. In this work, we report the design and synthesis of a highly active nanocatalyst, i.e., palladium and platinum nanoparticles (Pt&Pd-NPs) decorated ultrathin nanoporous gold (NPG) film, which is modified on a homemade graphene paper (GP) to develop a high-performance freestanding and flexible nanohybrid electrode. Owing to the structural characteristics the robust GP electrode substrate, and high electrochemically catalytic activities and durability of the permeable NPG support and ultrafine and high-density Pt&Pd-NPs on it, the resultant Pt&Pd-NPs-NPG/GP electrode exhibits excellent sensing performance of low detection limitation, high sensitivity and anti-interference capability, good reproducibility and long-term stability for the detection of small molecular biomarkers hydrogen peroxide (H 2 O 2 ) and glucose (Glu), and has been applied to the monitoring of H 2 O 2 in different types of live cells and Glu in body fluids such as urine and fingertip blood, which is of great significance for the clinical diagnosis and prognosis in point-of-care testing.

This article presents the development of a photothermal biosensing integrated with microfluidic paper-based analytical device (PT-μPAD) as a quantitative biosensor method for monitoring sarcosine in human control urine, plasma, and serum samples. The device utilizes gold nanoparticles (AuNPs) as both a peroxidase-like nanozyme and a photothermal substrate to enable sarcosine detection. In our PT-μPAD, hydrogen peroxide (H 2 O 2 ) is generated through the oxidation of sarcosine by a sarcosine oxidase (SOx) enzyme. Subsequently, the H 2 O 2 flows through the paper microchannels to the detection zone, where it etches the pre-deposited AuNPs, inducing a temperature change upon exposure by a 532 nm laser. The temperature variation is then measured using a portable and inexpensive infrared thermometer. Under optimized conditions, we obtained a linear range between 10.0 and 40.0 nmol L -1  (R 2  = 0.9954) and a detection limit (LOD) of 32.0 pmol L -1 . These values fall within the clinical range for sarcosine monitoring in prostate cancer diagnostics in humans. Moreover, our approach exhibits high selectivity without interfering effects. Recovery studies in various human control samples demonstrated a range of 99.05-102.11 % with the highest RSD of 2.25 %. The PT-μPAD was further validated for sarcosine determination in human control urine and compared with a commercial ELISA assay, revealing no significant difference between these two methods at a 95 % confidence level. Overall, our proposed sarcosine biosensor is well-suited for prostate cancer monitoring, given its affordability, sensitivity, and user-friendliness, even for unskilled individuals. Moreover, this strategy has promising prospects for broader applications, potentially detecting various biomarkers as a point-of-care (POC) diagnostic tool., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Background: Alzheimer's disease (AD), one of the most prevalent neurodegenerative diseases, results in severe cognitive decline and irreversible memory loss. Early detection of AD is significant to patients for personalized intervention since effective cure and treatment methods for AD are still lacking. Despite the severity of the disease, existing highly sensitive AD detection methods, including neuroimaging and brain deposit-positive lesion tests, are not suitable for screening purposes due to their high cost and complicated operation. Therefore, these methods are unsuitable for early detection, especially in low-resource settings. Although regular paper-based microfluidics are cost-efficient for AD detection, they are restricted by a poor limit of detection (LOD)., Results: To address the above limitations, we report the ultrasensitive and low-cost nanocellulose paper (nanopaper)-based analytical microfluidic devices (NanoPADs) for detecting one of the promising AD blood biomarkers (glial fibrillary acidic protein, GFAP) using Surface-enhanced Raman scattering (SERS) immunoassay. Nanopaper offers advantages as a SERS substrate, such as an ultrasmooth surface, high optical transparency, and tunable chemical properties. We detected the target GFAP in artificial serum, achieving a LOD of 150 fg mL -1 ., Significance: The developed NanoPADs are distinguished by their cost-efficiency and ease of implementation, presenting a promising avenue for effective early detection of AD's GFAP biomarker with ultrahigh sensitivity. More importantly, our work provides the experimental routes for SERS-based immunoassay of biomarkers on NanoPADs for various diseases in the future., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Herein, a cost-effective and portable microfluidic paper-based sensor is proposed for the simultaneous and rapid detection of glucose, free amino acids, and vitamin C in fruit. The device was constructed by embedding a poly(carboxybetaine acrylamide) (pCBAA)-modified cellulose paper chip within a hydrophobic acrylic plate. We successfully showcased the capabilities of a filter paper-based microfluidic sensor for the detection of fruit nutrients using three distinct colorimetric analyses. Within a single paper chip, we simultaneously detected glucose, free amino acids, and vitamin C in the vivid hues of cyan blue, purple, and Turnbull's blue, respectively, in three distinctive detection zones. Notably, we employed more stable silver nanoparticles for glucose detection, replacing the traditional peroxidase approach. The detection limits for glucose reached a low level of 0.049 mmol/L. Meanwhile, the detection limits for free amino acids and vitamin C were found to be 0.236 mmol/L and 0.125 mmol/L, respectively. The feasibility of the proposed sensor was validated in 13 different practical fruit samples using spectrophotometry. Cellulose paper utilizes capillary action to process trace fluids in tiny channels, and combined with pCBAA, which has superior hydrophilicity and anti-pollution properties, it greatly improves the sensitivity and practicality of paper-based sensors. Therefore, the paper-based colorimetric device is expected to provide technical support for the nutritional value assessment of fruits in the field of rapid detection.

Uric acid (UA) is an important biomarker, as a high concentration in blood can lead to gout and further renal syndrome. Although several point-of-care testing (POCT) devices have been reported to detect UA, there are some limitations such as the requirement for uricase and the complicated pretreatment of serum/plasma samples, which restricts their use at home or in undeveloped areas. In this work, we developed an approach by applying Zn 2+ to precipitate proteins and cells in whole blood to avoid interference with the chromogenic reaction. We used carboxymethylcellulose (CMC) to immobilize tetramethylbenzidine (TMB) on a nitrocellulose membrane for colorimetric detection. Using the oxidization properties of H 2 O 2 , which turns TMB into oxidized tetramethylbenzidine (TMBox) in the presence of catalyst gold nanoparticles (AuNPs), we successfully constructed an enzyme-free paper-based POCT device using the reduction reaction of UA and TMBox for simple, speedy, and cheap colorimetric detection of UA, achieving a detection time of 8 min, a linear range of 0-150 μg/mL, and an LOD of 25.79 μg/mL. The UA concentration in whole blood samples was further measured and correlated well with the clinical value (R 2  = 0.8212). Thus, the proposed assay has the potential for POCT diagnosis, monitoring, and prognosis of diseases related to UA., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.)

Herein, a flexible near-infrared (NIR) light-actuated photoelectrochemical (PEC) lab-on-paper device was constructed toward miRNA-122 detection, utilizing the combination of DNA-programmed NaYF 4 /Yb,Tm upconversion nanoparticles (UCNPs) and the Z -scheme AgI/WO 3 heterojunction grown in situ on gold nanoparticle-decorated 3D cellulose fibers. The UCNPs were employed as light transducers for converting NIR light into ultraviolet/visible (UV/vis) light to excite the nanojunction. The multiple diffraction of NaYF 4 /Yb,Tm matched the absorption band of the Z -scheme AgI/WO 3 heterojunction, resulting in enhanced PEC photocurrent output. This prepared Z -scheme heterojunction effectively directed charge migration and highly facilitated the electron-hole pair separation. Target miRNA-122 activated the nonenzyme catalytic hairpin assembly signal amplification strategy, generating duplexes which caused the exfoliation of NaYF 4 /Yb,Tm UCNPs from the biosensor electrode and lowered the photocurrent under 980 nm irradiation. Under optimized circumstances, the proposed NIR-actuated PEC lab-on-paper device presented accurate miRNA-122 detection within a wide linear range of 10 fM-100 nM with a low limit of detection of 2.32 fM, providing a reliable strategy in the exploration of NIR-actuated PEC biosensors for low-cost, high-performance bioassay in clinical applications.

As one of the essential trace elements in life activities, copper ion (Cu 2+ ) plays a very important role in human health. However, copper-containing pesticides are usually used for sterilization and disinfestation in agriculture. Thus, the residues of copper-containing pesticides in agricultural samples increase the risk of excessive intake of Cu 2+ for human. The development of an effective method for detecting Cu 2+ is still an important task. Herein, a detecting system based on AuNCs@ZIF-8 modified paper and smartphone platform was developed for visual detection of Cu 2+ in agricultural samples. Herein, a detecting system based on AuNCs@ZIF-8 modified paper and smartphone platform was developed for visual detection of Cu 2+ in agricultural samples. In the detecting system, gold nanoclusters (AuNCs) were packaged by ZIF-8 to limit their molecular motion and enhance the fluorescence effectively. In the meanwhile, by ultrasound-assisted biomimetic mineralizing, AuNCs@ZIF-8 composites were uniformly synthesized in situ on the surface of the paper fibers to indicate Cu 2+ by fluorescence quenching. A portable visual monitoring system consisted of the prepared Cu 2+ paper sensor and a smartphone platform was then successfully built and applied to on site detecting Cu 2+ in agricultural samples. The limit of detection (LOD) was 4.57 μM and recovery rate varied from 96.50 % to 121.58 %. The developed detecting system for Cu 2+ has the advantages of easy preparation and operation, and is very suitable for the use in agricultural products and farmland., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Glutathione (GSH) acts a crucial role in the normal operation of manifold life activities and is closely bound up with many human diseases. Here, a SERS-colorimetric bimodal paper-based biosensor based on Mn-doped CDs/silver nanoparticles (Mn-CDs/AgNPs) has been fabricated for high-efficiency quantification of intracellular GSH. The Mn-CDs/AgNPs with fine oxidase-like characteristic and SERS enhancement ability has been assembled onto the Whatman filter paper (WFP) to cleverly fabricate paper chip (Mn-CDs/AgNPs@WFP) which can trigger the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) into blue TMBox and simultaneously enhance the SERS signal of TMBox. However, the introduction of GSH inhibits the oxidation of TMB, leading to color fading of paper chip and diminishment of SERS signal. Considering this, the bimodal paper-based sensing platform can be exploited for SERS-colorimetric detection of GSH, manifesting excellent selectivity, reliable stability, and satisfactory precision. The detection limits of SERS and colorimetric detection modes are as low as 0.41 μM and 0.53 μM, respectively. Furthermore, this proposed bimodal biosensor has been successfully utilized for the determination of intracellular GSH and validated by commercial GSH assay kit, which provides a mighty and convenient tool for intracellular GSH detection and can boost future effort about exploitation of other multimode paper-based biosensors as well as promote their appliances in disease diagnosis., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Paper-based surface-enhanced Raman scattering (SERS) optical nanoprobes provide ultrasensitive analyte detection; however, they lack selectivity, making them difficult to use in real-world sample analysis without a pretreatment process. This work describes the design of a microfluidic paper-based SERS substrate based on molecularly imprinted nanogels decorated with silver nanoparticles to simultaneously detect bisphenol A (BPA) and bisphenol S (BPS) traces in plastic toys and receipts. The synthesized nanogels have two characteristics that boost SERS performance: molecularly imprinted cavities that allow for selective adsorption and a wrinkled surface that creates uniformly distributed hot spots. Simple paper-based sensor devices were built as 'drop and read' SERS substrates with a separate reservoir to detect a single target, while advanced SERS platforms were designed as a microfluidic chip with two reservoirs connected by a channel for simultaneous detection of BPA and BPS. The SERS platform with a single reservoir showed outstanding analytical performance for the detection of BPA and BPS, with low detection limits of 0.38 pM and 0.37 pM, respectively. The microfluidic paper-based sensor allowed simultaneous and selective detection of BPA and BPS with detection limits estimated at 0.68 nM and 0.47 nM, respectively. The developed sensors are successfully applied to detect BPA and BPS in plastic products and receipts. Finally, the results obtained with our method showed greater sensitivity than those of commercially available ELISA kits, and the acquired values within the ELISA detection range were in excellent agreement., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier B.V.)

Traditional paper-based packaging commonly needs to be coated to achieve sufficient mechanical and barrier performances. In this research, a bio-based coating for paper was developed from carbamate starch (Sc), calcium lignosulfonate (CL), and cellulose nanofibrils (CNF). Controlling the electrostatic and hydrogen-bonding interactions among the components of the coating was conducive to tailoring the structure and performance of the coated paper. When the degree of substitution (Ds) of Sc was 0.10, the amount of CL was 1.00 g, and the amount of CNF was 0.65 % of the weight of Sc, the paper coated with the resulting 0.10Sc-1.00CL-0.65CNF coating exhibited increased hydrophobicity and excellent mechanical, air-barrier, and UV-light-barrier properties. After the addition of 0.10 % of silver nano-particles (AgNPs) to the 0.10Sc-1.00CL-0.65CNF coating, the paper coated with the resulting 0.10Sc-1.00CL-0.65CNF-0.10AgNPs coating exhibited good antibacterial activity against Escherichia coli and Staphylococcus aureus. The coated paper was used as the packaging for cherry tomatoes stored under ambient conditions. Due to the synergistic preservation effects of the Sc-CL-CNF coating and AgNPs, the shelf life of the cherry tomatoes was at least 7 days. The coated paper described herein has the potential for applications in the food packaging sector., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

A combination of multiple methods can greatly intensify the removal efficiency of hazardous substances. Herein, the synergistic utilization of adsorption and catalysis achieved for the highly efficient removal of hexavalent chromium (Cr 6+ ). A paper-based palladium nanoparticles/UiO-66-NH 2 (PdNPs/UiO-66-NH 2 /LP) composite catalyst was prepared using lignocellulose paper-based material (LP) for the loading of UiO-66-NH 2 MOFs materials, with the lignin in LP as the reducer for the in-situ synthesis of PdNPs (12.3 nm) on UiO-66-NH 2 MOF materials. Lignocellulose paper-based materials with high strength (82 N·m/g) realized low-cost and environmentally friendly preparation and guaranteed the practicability of PdNPs/UiO-66-NH 2 /LP composite catalyst. The prepared PdNPs/UiO-66-NH 2 /LP achieved high-efficiency catalytic activity for hazardous Cr 6+ removal through a constructed adsorption-catalytic synergistic system, in which the removal efficiency of Cr 6+ in 10 min was increased by 2 times compared with a composite catalyst without MOFs loading. Finally, the PdNPs/UiO-66-NH 2 /LP composite catalyst demonstrated the great efficiency and practicality of water pollution treatment through synergistic adsorption enrichment and catalytic reduction., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

In this study, nanomaterials capable of enzyme-free glucose quantification and colorimetric readout are integrated into a microfluidic paper-based analytical devices (μPADs). Gold nanoparticles (AuNPs) and silver nanoparticles (AgNPs) were utilized as a peroxidase-like nanozyme and a colorimetric probe to achieve glucose monitoring. In this developed device, glucose is oxidized by AuNPs to generate hydrogen peroxide (H 2 O 2 ), which flows in the paper microchannels toward detection zones. H 2 O 2 then etches the immobilized AgNPs to induce a color change. The intensity of color change is easily monitored using a smartphone application. Following method optimization, we obtained a linear range from 0.50 to 10.0 mmol L -1  (R 2  = 0.9921) and a detection limit (LOD) of 340.0 μmol L -1 . This falls in the clinically relevant range for glucose monitoring and diabetes diagnosis in humans. In addition, the total analysis time is just 20 min, which is significantly less than the same experiment performed in the solution phase. Also, our method is markedly selective; other substrates do not interfere. The recovery test in human control samples was in the range of 98.47-102.34% and the highest relative standard deviation (RSD) was 3.58%. The enzyme-free approach for glucose sensing is highly desirable for diabetes diagnosis as it replaces the more expensive enzyme with cheaper nanomaterials. Furthermore, since nanomaterials are more environmentally stable compared to enzymes, it has the potential for widespread deployment as point-of-care diagnostics (POC) in resource-limited settings., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

MicroRNAs (miRNAs) have emerged as a promising class of biomarkers for early detection of various cancers, including ovarian cancer. However, quantifying miRNAs in human blood samples is challenging owing to the issues of sensitivity and specificity. In this study, hsa-miR-200a-3p of the miR-200a sub-family, which is a biomarker of ovarian cancer, was used as the analyte to demonstrate the analytical capability of an integrated biosensing platform using an extremely sensitive surface-enhanced Raman scattering (SERS) nanotag-nanoaggregate-embedded beads (NAEBs), magnetic nanoparticles (MNPs), a pair of highly specific locked nucleic acid (LNA) probes, and a semi-automated paper-based electrowetting-on-dielectric (pEWOD) device to provide labor-less and thorough sample cleanup and recovery. A sandwich approach where NAEBs are modified by one LNA-1 probe and MNPs are modified by another LNA-2 probe was applied. Then, the target analyte miRNA-200a-3p was introduced to form a sandwich nanocomplex through hybridization with the pair of LNA probes. The pEWOD device was used to achieve short cleanup time and good recovery of the nanocomplex, bringing the total analysis time to less than 30 min. The detection limit of this approach can reach 0.26 fM through SERS detection. The versatility of this method without the need for RNA extraction from clinical samples is expected to have good potential in detecting other miRNAs.

In this study, we demonstrate that palladium-platinum bimetallic nanoparticles (Pd@Pt NPs) as the nanozyme, combined with a multi-layer paper-based analytical device and DNA hybridization, can successfully detect Mycobacterium tuberculosis . This nanozyme has peroxidase-like properties, which can increase the oxidation rate of the substrate. Compared with horseradish peroxidase, which is widely used in traditional detection, the Michaelis constants of Pd@Pt NPs are fourteen and seventeen times lower than those for 3,3',5,5'-tetramethylbenzidine and H 2 O 2 , respectively. To verify the catalytic efficiency of Pd@Pt NPs, this study will execute molecular diagnosis of Mycobacterium tuberculosis . We chose the IS 6110 fragment as the target DNA and divided the complementary sequences into the capture DNA and reporter DNA. They were modified on paper and Pd@Pt NPs, respectively, to detect Mycobacterium tuberculosis on a paper-based analytical device. With the above-mentioned method, we can detect target DNA within 15 minutes with a linear range between 0.75 and 10 nM, and a detection limit of 0.216 nM. These results demonstrate that the proposed platform (a DNA-nanozyme integrated paper-based analytical device, dnPAD) can provide sensitive and on-site infection prognosis in areas with insufficient medical resources.

Herein, a versatile surface enhanced Raman scattering (SERS) platform was firstly constructed by integrating conductive metal organic framework (CMOF) with controlled electrodeposition of Au nanoparticles (Au NPs) on flexible carbon paper (CP-CMOF@Au) for sensitively recognizing diazepam (DZP) in aquatic products. The CMOF not only provided a pre-concentration effect for boosting sensitivity, but also dramatically improved the intrinsic electrical conductivity contributing to homogeneous distribution of Au NPs and forming SERS-active "hot spot" with superior stability and reproducibility. Based on CP-CMOF@Au chip, DZP can be sensitively detected with low limit of detection of 0.64 ng mL -1 and wide linear detection range from 0.001 to 10 μg mL -1 . Also, DZP in aquatic products can be collected and recognized using multiple approaches (drip coating, soaking and wiping) with excellent reusability and satisfactory recovery of 85.8-103.3%. This method would provide an ingenious SERS strategy for rapidly monitoring DZP in aquatic products with good practical applicability., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Engineered collaborative biochemical techniques and regulated nanomaterials (NMs) offer extraordinary opportunities for improving the analysis performance of lateral flow immunoassay (LFIA). Herein, inspired by the ability of macromolecules (e.g., proteins) to assemble into new functional units and the remarkable optical performance of engineered regulated NMs, goat anti-mouse immunoglobulin (GAMI) serves as the "crosslinker" integrate with gold‑manganese oxide (Au-MnO x ) to assemble the "signal tracers (STs)-crosslinker-antibody (mAb)" for elevating the mAb utilization efficiency. Notably, the "STs-crosslinker-mAb" assembly shows ~13.33-folds mAb utilization efficiency enhance, which perfectly response the challenge between limited sensitivity and sufficient signal intensity in competitive-type LFIA. The black color and rough structure of Au-MnO x offer higher colorimetric brightness (~2-folds than AuNPs) and enhanced mAb coupling efficiency (up to 92.47%), which further improves sensitivity under the premise of functional assembly to intensify the competitive immunoreaction. Additionally, the convenient synthesis conditions (~13 min at room temperature) even comparable to direct purchase commercial products indicate that using Au-MnO x undoubtedly increases the cost-effectiveness. Encouragingly, the Au-MnO x -GAMI-mAb based LFIA exhibited high sensitivity (LOD: 0.063 ng mL -1 for clenbuterol (CLE) monitoring) by elevating mAb utilization efficiency with the attendant enhancing immune competition response in a cost-effective manner, which provides an invigorating reference pathway in point-of-care immunoassay., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

A label-free detection method for noninvasive biofluids enables rapid on-site disease screening and early-stage cancer diagnosis by analyzing metabolic alterations. Herein, we develop three-dimensional plasmonic hexaplex nanostructures coated on a paper substrate (3D-PHP). This flexible and highly absorptive 3D-PHP sensor is integrated with commercial saliva collection tube to create an efficient on-site sensing platform for lung cancer screening via surface-enhanced Raman scattering (SERS) measurement of human saliva. The multispike hexaplex-shaped gold nanostructure enhances contact with saliva viscosity, enabling effective sampling and SERS enhancement. Through testing patient salivary samples, the 3D-PHP sensor demonstrates successful lung cancer detection and diagnosis. A logistic regression-based machine learning model successfully classifies benign and malignant patients, exhibiting high clinical sensitivity and specificity. Additionally, important Raman peak positions related to different lung cancer stages are investigated, suggesting insights for early-stage cancer diagnosis. Integrating 3D-PHP senor with the conventional saliva collection tube platform is expected to offer promising practicality for rapid on-site disease screening and diagnosis, and significant advancements in cancer detection and patient care., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier B.V. All rights reserved.)

Staphylococcus aureus is a gram-positive bacterium that can easily cause outbreaks of food-borne diseases. In this work, a signal-enhanced three-dimensional paper-based photoelectrochemical (PEC) aptsensor for the rapid and sensitive determination of S. aureus was developed. Specifically, gold nanoparticles (AuNPs) were electrodeposited on a paper-based working electrode to provide binding sites for a sulfhydryl-functionalized aptamer. Subsequently, S. aureus was captured with high specificity by a carboxyl-functionalized aptamer modified with amino-functionalized AgBiS 2 nanoflowers (NH 2 -AgBiS 2 NFs), which functionalized as PEC probes that generated strong photocurrent under irradiation with 980-nm light. By exploiting the "aptamer-target-aptamer" PEC sensing platform, the rapid and ultrasensitive detection of S. aureus was achieved. The sensor had a wide linear range of 20 to 2 × 10 7  CFU/mL and low limit of detection of 4 CFU/mL. Further, the applicability of the as-prepared aptsensor was successfully certified for the analysis of pork samples artificially contaminated with S. aureus., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Background: Flexible surface-enhanced Raman spectroscopy (SERS) substrates such as paper-based substrates show great potential for rapid detection of residual chemicals on food surfaces. However, controlling the density and distribution of metallic nanoparticles adsorbed on the paper is still challenging., Results: The amount of gold (Au) nanospheres (51 ± 4 nm) attached on the filter paper modified with 3-aminopropyltriethoxysilane (APTES) was tunable, increasing as the level of APTES (2.5-15.0 g kg -1 ) applied for paper modification increased. Moreover, the Au nanospheres were relative evenly distributed on the filter paper modified with 2.5-10.0 g kg -1 of APTES, which resulted in excellent intra- and inter-reproducibility of SERS signals for pesticides including thiram, diquat dibromide, and paraquat dichloride (relative standard deviation = 2.2-10.1%). The modified paper-based substrate could be used to detect as low as 0.05-0.2 mg L -1 of pesticides in standard solutions, and as low as 5-20 ng cm -2 of residual pesticides on apple skins with minimum sample pretreatment., Conclusion: This paper-based substrate with tunable feature for the density and distribution of nanoparticles is applicable for rapid SERS detection of residual pesticides in fruits and vegetables. © 2023 Society of Chemical Industry., (© 2023 Society of Chemical Industry.)

The precise detection of pathogenic microorganisms is crucial for the reduction of water-borne diseases. Herein, a filter-paper-based florescent chemosensor was fabricated for the detection of Escherichia coli and Staphylococcus aureus contamination exploiting protein-DNA interaction between the target and a specific probe. The sensing mechanism involved the self-assembly of Rhodamine B (RhB) on silver nanoparticles (AgNPs) surface that was labeled with a single-stranded DNA probe. This causes the fluorescence quenching of RhB by a distant-dependant process. The hybridization between pathogen-specific probe and bacterial surface protein causes the release of fluorescence of RhB, which was observed under UV light. For paper-based bio-surface preparation, the mixture comprising RhB-AgNP-ssDNA was drop-casted on filter paper discs. The conditions were optimized using isolated genomic DNA of the microbes. The method was applied for E.coli detection using an eae gene-based probe targeting intimin protein and S. aureus detection using tuf gene-based probe targeting EF-tuf protein on the microbe's surface. The chemosensor had a notable specificity and selectivity for E.coli, and S. aureus, with detection limits of 0.6 × 10 8 and 0.37 × 10 3  CFU/mL respectively. Moreover, the sensor was tested on real water samples, which presented excellent reproducibility of results (RSD ≤ 0.24%). Furthermore, the gradient change of fluorescence was captured by a smartphone, which allows direct detection of pathogens in a sensitive semi-quantitative way without the need for expensive instruments. The designed chemosensor can serve as a simple, inexpensive, and rapid method for the on-site detection of microbial contamination in drinking water., (© 2023. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

This study presents a rapid microfluidic paper-based analytical device (μPAD) capable of simultaneously monitoring Gram-negative bacteria and nitrite ions (NO 2 - ) for water quality monitoring. We utilize gold nanoparticles (AuNPs) functionalized with polymyxin molecules (AuNPs@polymyxin) to cause color change due to aggregation for the detection of Gram-negative bacteria, and antiaggregation in the presence of o -phenylenediamine (OPD) for NO 2 - detection. In this study, Escherichia coli ( E. coli ) serves as the model of a Gram-negative bacterium. Using the developed μPADs, the color changes resulting from aggregation and antiaggregation reactions are measured using a smartphone application. The linear detection ranges from 5.0 × 10 2 to 5.0 × 10 5 CFU/mL ( R 2 = 0.9961) for E. coli and 0.20 to 2.0 μmol/L ( R 2 = 0.995) for NO 2 - . The detection limits were determined as 2.0 × 10 2 CFU/mL for E. coli and 0.18 μmol/L for NO 2 - . Notably, the newly developed assay exhibited high selectivity with no interference from Gram-positive bacteria. Additionally, we obtained acceptable recovery for monitoring E. coli and NO 2 - in drinking water samples with no significant difference between our method and a commercial assay by t test validation. The sensor was also employed for assessing the quality of the pond and environmental water source. Notably, this approach can also be applied to human urine samples with satisfactory accuracy. Furthermore, the assay's stability is extended due to its reliance on AuNPs rather than reagents like antibodies and enzymes, reducing costs and ensuring long-term viability. Our cost-effective μPADs therefore provide a real-time analysis of both contaminants, making them suitable for assessing water quality in resource-limited settings.

Detecting sputum pyocyanin (PYO) with a competitive immunoassay is a promising approach for diagnosing Pseudomonas aeruginosa respiratory infections. However, it is not possible to perform a negative control to evaluate matrix-effects in competitive immunoassays, and the highly complex sputum matrix often interferes with target detection. Here, we show that these issues are alleviated by performing competitive immunoassays with a paper biosensor. The biosensing platform consists of a paper reservoir, which contains antibody-coated gold nanoparticles, and a substrate containing a competing recognition element, which is a piece of paper modified with an albumin-antigen conjugate. Detection of PYO with a limit of detection of 4.7·10 -3  µM and a dynamic range between 4.7·10 -1  µM and 47.6 µM is accomplished by adding the sample to the substrate with the competing element and pressing the reservoir against it for 5 min. When tested with patient samples, the biosensor was able to qualitatively differentiate spiked from non-spiked samples, whereas ELISA did not show a clear cut-off between them. Furthermore, the relative standard deviation was lower when determining sputum with the paper-based biosensor. These features, along with a mild liquefaction step that circumvents the use of harsh chemicals or instruments, make our biosensor a good candidate for diagnosing Pseudomonas infections at the bedside through the detection of sputum PYO., (© 2023. The Author(s).)

Acyclovir (ACV) drug, a common antiviral agent, is frequently used as the primary clinical treatment method for treating hepatitis B, herpes simplex, and varicella zoster viruses due to its potent therapeutic effect. In patients with compromised immune systems, this medication can stop cytomegalovirus infections, and high doses of this drug are required; however, such prescription leads to kidney toxicity. Therefore, timely and accurate detection of ACV is crucial in many areas. Surface-Enhanced Raman Scattering (SERS) is a reliable, rapid, and precise approach for the identification of trace biomaterials and chemicals. Filter paper substrates decorated with silver nanoparticles (AgNPs) were applied as SERS biosensors to detect ACV and control its adverse effects. Initially, a chemical reduction procedure was utilized to produce AgNPs. Afterward, UV-Vis, FE-SEM, XRD, TEM, DLS, and AFM were employed to examine the properties of prepared AgNPs. In order to prepare SERS-active filter paper substrates (SERS-FPS) to detect Molecular vibrations of ACV, AgNPs prepared by immersion method were coated on filter paper substrates. Moreover, the UV-Vis DRS analysis was carried out to assess the stability of filter paper substrates and SERS-FPS. The AgNPs reacted with ACV after being coated on SERS-active plasmonic substrates and could sensitively detect ACV in small concentrations. It was discovered that the limit of detection of SERS plasmonic substrates was 10 -12 M. Moreover, the mean RSD for ten repeated tests was calculated as 4.19%. The enhancement factor for detecting ACV using the developed biosensors was calculated to be 3.024 × 10 5 and 3.058 × 10 5 experimentally and via simulation, respectively. According to the Raman results, SERS-FPS for the detection of ACV, fabricated by the present methods, showed promising results for SERS-based investigations. Furthermore, these substrates showed significant disposablity, reproducibility, and chemical stability. Therefore, the fabricated substrates are capable to be employed as potential SERS biosensors to detect trace substances., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Bacterial infections caused by pathogenic microorganisms have become a serious, widespread health concern. Thus, it is essential and required to develop a multifunctional platform that can rapidly and accurately determine bacteria and effectively inhibit or inactivate pathogens. Herein, a microarray SERS chip was successfully synthesized using novel metal/semiconductor composites (ZnO@Ag)-ZnO nanoflowers (ZnO NFs) decorated with Ag nanoparticles (Ag NPs) arrayed on a paper-based chip as a supporting substrate for in situ monitoring and photocatalytic inactivation of pathogenic bacteria. Typical Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli and Vibrio parahemolyticus were selected as models. Partial least-squares discriminant analysis (PLS-DA) was performed to minimize the dimensionality of SERS spectra data sets and to develop a cost-effective identification model. The classification accuracy was 100, 97.2, and 100% for S. aureus , E. coli , and V. parahemolyticus , respectively. The antimicrobial activity of ZnO@Ag was proved by the microbroth dilution method, and the minimum inhibitory concentrations (MICs) of S. aureus , E. coli , and V. parahemolyticus were 40, 50, and 55 μg/mL, respectively. Meanwhile, it demonstrated remarkable photocatalytic performance under natural sunlight for the inactivation of pathogenic bacteria, and the inactivation rates for S. aureus , E. coli , and V. parahemolyticus were 100, 97.03 and 97.56%, respectively. As a result, the microarray chip not only detected the bacteria with high sensitivity but also confirmed the antibacterial and photocatalytic sterilization properties. Consequently, it offers highly prospective strategies for foodborne diseases caused by pathogenic bacteria.

The surface modification of filters with large pore sizes for the development of low-cost gravity-driven point-of-use (POU) technologies for water disinfection can be an effective strategy to empower people to access safe water instantly, especially in low- and middle-income countries. In this study, the surface of commercial cellulose filter papers, as cheap and bio-based filters, was modified with polydopamine (PDA), polyethyleneimine (PEI) and ZnO/Ag/GO nanocomposite (ZnO/Ag/GO@PDA/PEI papers) for bacterial removal from water. PDA/PEI incorporation introduced a cationic functional layer, which can entrap negative bacteria and make a stable chemical bond with the nanocomposite. ZnO/Ag/GO exhibited promising synergistic antibacterial activities (30 times stronger than ZnO). As a result, 3 sheets of ZnO/Ag/GO@PDA/PEI papers showed a 99.98% bacterial reduction (E. coli), which met the WHO standards. Moreover, the leached zinc and silver in the filtrate were far below the WHO's limits (380 and 10 ppb, respectively). The results showed that the modified papers could be reused multiple times. After six times of reuse, the flow rate dropped slightly (below 20%) and the bacterial removal efficiency was more than 99.9%. This study is valuable for developing filters for treating bacterial-contaminated water on-site with no need for energy, which is a demand in many countries., (© 2023. The Author(s).)

Fast detection of contaminants of emerging concern (CECs) in water resources is of great environmental interest. Ideally, sustainable materials should be used in water quality monitoring technologies implemented for such purposes. In this regard, the application of bio-based materials aimed at the fabrication of analytical platforms has become of great importance. This research merges both endeavors by exploring the application of chitosan-coated paper, decorated with silver nanoparticles (AgNPs), on surface-enhanced Raman scattering (SERS) spectroscopy studies of two distinct types of CECs dissolved in aqueous samples: an antibiotic (ciprofloxacin) and a pesticide (thiram). Our results indicate the superior SERS performance of biocoated substrates compared to their non-coated paper counterparts. The detection limits achieved for thiram and ciprofloxacin using the biocoated substrates were 0.024 ppm and 7.7 ppm, respectively. The efficient detection of both analytes is interpreted in terms of the role of the biopolymer in promoting AgNPs assemblies that result in local regions of enhanced SERS activity. Taking advantage of these observations, we use confocal Raman microscopy to obtain Raman images of the substrates using ciprofloxacin and thiram as molecular probes. We also demonstrate that these biobased substrates can be promising for on-site analysis when used in conjunction with portable Raman instruments.

Permethrin is a pyrethroid pesticide and insect repellent that prevents mosquito-borne infections like dengue and malaria in tropical areas. This work describes a new colorimetric sensor based on metronidazole-stabilized silver nanoparticles (MTZ-AgNPs) for the first rapid, sensitive, and selective permethrin detection. The MTZ-AgNPs-based colorimetric sensor has a limit of detection (LOD) of 0.0104 µM and a limit of quantification (LOQ) of 0.0348 µM, respectively. The sensor is further integrated with smartphone and microfluidic fabrication of paper-based analytical devices (µPADs) for real-time and on-site detection of permethrin. Under optimal settings, no potential environmental contaminants interfere with permethrin detection, confirming its high selectivity. Finally, the practical applicability of sensors is confirmed in real tomato and apple extract samples. The US environmental protection agency's recommended UPLC method validated the detection efficiency of the proposed colorimetric sensor. The % recoveries from UPLC and MTZ-AgNPs suggest that the present sensor can quantitatively analyze permethrin in real samples., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Fumonisin B1 (FB1), as one of the highest toxicity mycotoxins, poses a serious threat to animal and human health, even at low concentrations. It is significant and challenging to develop a sensitive and reliable analytical device. Herein, a paper-based electrochemical aptasensor was designed utilizing tetrahedral DNA nanostructures (TDNs) to controllably anchor an aptamer (Apt), improving the recognition efficiency of Apt to its target. First, gold nanoparticles (AuNPs)@MXenes were used as a sensing substrate with good conductivity and modified on the electrode for immobilization of complementary DNA-TDNs (cDNA-TDNs). In the absence of FB1, numerous Apt-Au@Pt nanocrystals (NCs) was hybridized with cDNA and assembled on the sensing interface, which accelerated the oxidation of TMB with H 2 O 2 and produced a highly amplified differential pulse voltammetry (DPV) signal. When the target FB1 specifically bound to its Apt, the electrochemical signal was decreased by releasing the Apt-Au@Pt NCs from double-stranded DNA (dsDNA). On account of the strand displacement reaction by FB1 triggering, the aptasensor had a wider dynamic linear range (from 50 fg/mL to 100 ng/mL) with a lower limit of detection (21 fg/mL) under the optimized conditions. More impressively, the designed FB1 aptasensor exhibited satisfactory performance in corn and wheat samples. Therefore, the TDN-engineered sensing platform opens an effective approach for sensitive and accurate analysis of FB1, holding strong potential in food safety and public health.

This study introduces a thermoplastic microdevice integrated with additive-enhanced allele-specific amplification and hydrazine-induced silver nanoparticle-based detection of single nucleotide polymorphism (SNP) and opportunistic pathogens. For point-of-care testing of SNP, an allele-specific loop-mediated isothermal amplification reaction using nucleotide-mismatched primers and molecular additives was evaluated to discriminate single-nucleotide differences in the samples. The microdevice consists of purification and reaction units that enable DNA purification, amplification, and detection in a sequential manner. The purification unit enables the silica-based preparation of samples using an embedded glass fiber membrane. Hydrazine-induced silver nanoparticle formation was employed for endpoint colorimetric detection of amplicons within three min at room temperature. The versatile applicability of the microdevice was demonstrated by the successful identification of SNPs related to sickle cell anemia, genetically-induced hair loss, and Enterococcus faecium . The microdevice exhibited a detection limit of 10 3 copies per μL of SNP targets in serum and 10 2 CFU mL -1 of Enterococcus faecium in tap water within 70 min. The proposed microdevice is a promising and versatile platform for point-of-care nucleic acid testing of different samples in low-resource settings.

The goal of food safety supervision is to directly identify the pesticide residues on the surface of fruits and vegetables. This study proposed to develop a facile, non-destructive, and sensitive method based on surface-enhanced Raman scattering (SERS) to detect non-systemic pesticides on the surface of fruits and vegetables. The composite material was prepared by loading CTAB guided Au@Ag NRs with positive charge onto filter paper which was modified with PDADMAC(+) and PSS(-) using electrostatic adsorption. Au@Ag NRs with bimetallic synergies were effectively adsorbed in the fiber grid to generate 3D SERS hotspots within a few microns of depth. The results showed that the 3D composite flexible substrate had a high SERS activity, great repeatability, and sensitivity when the method was utilized to detect 4-MBA, methyl-parathion, thiram and chlorpyrifos. Three kinds of non-systemic pesticides on the peel could be detected directly and quickly owing to the arbitrary bending of the substrate, demonstrating the efficiency of the SERS "paste-reading" method. The acquired findings demonstrated that PDADMAC/PSS/Au@Ag NRs composite filter paper had the potential to provide rapid feedback for in-situ analysis of pesticide residues on the surface of fruit and vegetable., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier Ltd.)

In order to facilitate monitoring of cannabidiol (CBD), we devised a gold immunochromatographic sensor based on a specific monoclonal antibody (mAb). To prepare the antigen, a novel hapten with CBD moiety and a linear carbon chain was employed. By utilizing hybridoma technology, a specific mAb was screened and identified that exhibited a 50% maximal inhibitory concentration against CBD ranging from 28.97 to 443.97 ng/mL. Extensive optimization led to the establishment of visual limits of detection for CBD, achieving a remarkable sensitivity of 8 μg/mL in the assay buffer. To showcase the accuracy and stability, an analysis of CBD-spiked wine, sparkling water, and sports drink was conducted. The recovery rates observed were as follows: 88.4-109.2% for wine, 89.9-107.8% for sparkling water, and 83.2-95.5% for sports drink. Furthermore, the coefficient of variation remained impressively low, less than 4.38% for wine, less than 2.07% for sparkling water, and less than 6.34% for sports drink. Importantly, the developed sensor exhibited no cross-reaction with tetrahydrocannabinol (THC). In conclusion, the proposed paper sensor, employing gold nanoparticles, offers a user-friendly and efficient approach for the precise, rapid, and dependable determination of CBD in products.

The highly efficient and accurate recognition of targeted allergens is an essential element in the diagnosis of allergic diseases and follow-up desensitization treatment in clinic. The current clinical methods widely used to detect sIgE are high cost, time-consuming procedures, and bulky equipment. Herein, a multiplex microfluidic paper-based device (multi-μPAD) was developed that combined with tailored gold nanoparticles for simultaneously visual, colorimetric detection of different allergens in serum. This device could be used as quantitative detection of sIgE with LOD as low as 0.246 KUA/L in colorimetric method. In vitro results also showed that this device possessed good repeatability, high accuracy and incredible stability in different pH (6.0-7.4) and temperature (24-37 °C), as well as long-term storage within 90-day. Finally, this method was successfully utilized for assessing clinical multi-sample screening in 35 allergic patients. After the addition of the samples from allergic patients, the agreement rate of clinical results with commercial enzyme-linked immunosorbent assay (ELISA) kit reached more than 97%, which further indicated that this device had the advantages of efficient, accurate and sensitive to screen various allergens in real clinical serum samples. Therefore, by simply altering antigens and antibodies, this device can also be used for high-throughput detection of other allergens, making it considerable potential for clinical diagnosis of allergic diseases., Competing Interests: Declaration of competing interest The authors declared that they have no conflicts of interest to this work., (Copyright © 2023. Published by Elsevier B.V.)

The separation of enantiomers plays a critical role in pharmaceutical development, ensuring therapeutic efficacy, safety, and patent protection. It enables the production of enantiopure drugs and enhances our understanding of the properties of chiral compounds. In this study, a straightforward and effective chiral detection strategy was developed for distinguishing between tryptophan (TRP) enantiomers. The approach involved the preparation of a magnetic molecularly imprinted chitosan (MMIC) for preparation of the sample, which was combined with a nitrocellulose membrane (a paper-based analytical device, PAD) integrated with D-TRP covalently grafted with polymethacrylic acid (PAD-PMA_D-TRP). Discriminating between the TRP enantiomers was achieved using AuNPs as a colorimetric probe. Indeed, the presence of D-TRP rapidly induced the aggregation of AuNPs due to its strong affinity to PAD-PMA_D-TRP, resulting in a noticeable change in the color of the AuNPs from red to purple. On the other hand, L-TRP did not induce any color changes. The chiral analysis could be easily performed with the naked eye and/or a smartphone. The developed method exhibited a detection limit of 3.3 µM, and it was successfully applied to detect TRP in serum samples, demonstrating good recovery rates. The proposed procedure is characterized by its simplicity, cost-effectiveness, rapidity, and ease of operation.

Among the different analytical techniques, surface-enhanced Raman scattering (SERS) approach is a widely used technique for the detection and analysis of various chemicals and biological samples. Present study reports a low-cost, sensitive SERS substrate that has an ability to detect rotavirus in clinical stool samples. The proposed SERS substrate has been fabricated through drop-casting of silver nanoparticles (AgNPs) on a printing-grade paper. Rotavirus particles were extracted from clinical stool samples. The presence of rotavirus antigen in stool samples was confirmed using enzyme-linked immunosorbent assay (ELISA), polymerase chain reaction (PCR), and sequencing. The characteristic Raman peaks of rotavirus (RV) particles in solution were found to be significantly enhanced when Raman signals were recorded from the paper-based SERS substrates. Using the proposed SERS substrate, rotavirus samples with concentration as low as 1% could be reliably recorded by the Raman spectrometer. The paper SERS substrate reported herein is an extremely cost-efficient platform and may find applications in other research and clinical laboratories as well., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Heavy metals released by anthropogenic activities are extremely toxic to animals and plants due to their bioaccumulative and persistent environmental presence. In the current study, silver nanoparticles (AgNPs) were synthesized utilizing eco-friendly processes, and their potential in colorimetric Hg 2+ ion sensing in environmental samples was examined. An aqueous extract of Hemidesmus indicus root (Sarsaparilla Root, ISR) rapidly converts silver ions into AgNPs within 5 min of exposure to sunlight. Transmission electron microscopy confirms that ISR-AgNPs are spherical, ranging from 15 to 35 nm. Fourier-transform infrared spectroscopy revealed phytomolecules stabilized the NPs with hydroxyl and carbonyl substituents. The ISR-AgNPs detect Hg 2+ ions by a colour change that can be seen with the naked eye within 1 min. The probe is interference-free and detects the presence of Hg 2+ ions in sewage water. A method for fabricating ISR-AgNPs onto paper was disclosed, and this portable ISR-AgNPs embedded paper device was found to be good at sensing mercury present in the water. The findings show that environmentally friendly synthesized AgNPs can contribute to developing onsite colorimetric sensors., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Nutraceuticals are promoted and marketed with the stated label of being natural as well as safe herbal products. In order to enhance their effectiveness, nutraceuticals are usually adulterated with undeclared constituents. Slimming herbs may contain sibutramine (SBT) which is an FDA-banned ingredient due to its fatal outcomes. This current work's aim is to design a trimodal sensor for SBT detection in different herbal slimming formulations. Screen-printed silver and multi-walled carbon nanotube inks were employed for the potentiometric sensor. The sensor was designed to fill a reaction well in which a carbon dot-silver nanoparticle pair was applied for fluorimetric and colorimetric purposes. The trimodal sensor was designed to fit an 8 mm 2-pin LED strip connector. Potentiometric measurement took place upon application of one sample aliquot then the optical reaction proceeded next in a specified zone for optical detection. These multiple detection mechanisms achieved the required selectivity for SBT determination in the presence of other slimming products' additives. This trimodal sensor satisfied World Health Organization standards for point-of-care devices demonstrating the suggested device as a dynamic part for rapid on-site detection of undisclosed SBT.

Paper coating plays an important role in the paper properties, printability and application. The nanocoating is a multifunction layer that provides the paper with unique features. In this work, nanocoating formulas were prepared using a green method and component. The nanocoating formulas were based on biopolymers nanostarch NSt and nanochitosan NCh (NCS) decorated with Egyptian kaolinite Ka doped with zinc nanoparticles NCS@xka/ZnONPs (x represents different ratios) support for multifunctional uses. The nanocoating formulas were characterized using a physiochemical analysis as well as a topographical study. FTIR, XRD, SEM and TEM techniques were used. Additionally, the antimicrobial activity of the tested samples was assessed against six microorganisms including Gram-negative and Gram-positive bacteria. The prepared nanocoating formulas affirmed excellent antimicrobial activity as a broad-spectrum antimicrobial active agent with excellent activity against all representative microbial communities. The nanocoating with the highest ratio of Ka/ZnONPs (NCS@40 ka/ZnONPs) showed excellent antimicrobial activity with an inhibition percentage of more than 70% versus all microorganisms presented. The paper was coated with the prepared suspensions and characterized concerning optical, mechanical and physical properties. When Ka/ZnONPs were loaded into NCS in a variety of ratios, the characteristics of coated paper were enhanced compared to blank paper. The sample NCS@40 ka/ZnONPs increased tensile strength by 11%, reduced light scattering by 12%, and improved brightness and whiteness by 1%. Paper coated with NCh suspension had 35.32% less roughness and 188.6% less porosity. When coated with the sample NCS@10 ka/ZnONPs, the coated paper's porosity was reduced by 94% and its roughness was reduced by 10.85%. The greatest reduction in water absorptivity was attained by coating with the same sample, with a reduction percentage of 132%., (© 2023. The Author(s).)

Surface-Enhanced Raman Spectroscopy (SERS) is a powerful surface-sensitive technique for molecular analysis. Its use is limited due to high cost, non-flexible rigid substrates such as silicon, alumina or glass and less reproducibility due to non-uniform surface. Recently, paper-based SERS substrates, a low-cost and highly flexible alternative, received significant attention. We report here a rapid, inexpensive method for chitosan-reduced, in-situ synthesis of gold nanoparticles (GNPs) on paper devices towards direct utilization as SERS substrates. GNPs have been prepared by reducing chloroauric acid with chitosan as a reducing and capping reagent on the cellulose-based paper surface at 100 °C, under the saturated humidity condition (100 % humidity). GNPs thus obtained were uniformly distributed on the surface and had fairly uniform particle size with a diameter of 10 ± 2 nm. Substrate coverage of resulting GNPs directly depended on the precursor's ratio, temperature and reaction time. Techniques such as TEM, SEM, and FE-SEM were utilized to determine the shape, size, and distribution of GNPs on paper substrate. SERS substrate produced by this simple, rapid, reproducible and robust method of chitosan-reduced, in situ synthesis of GNPs, showed exceptional performance and long-term stability, with a detection limit of up to 1 pM concentration of test analyte, R6G. Present paper-based SERS substrates are cost-effective, reproducible, flexible, and suitable for field applications., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Saurabh Kumar Srivastava reports that the SERB-National Postdoctoral Fellowship provided financial support from the Department of Science and Technology, New Delhi, India., (Copyright © 2023. Published by Elsevier B.V.)

In order to prompt the appearance of the shrimp color, sodium metabisulfite is frequently added in shrimp processing, which is, however, prohibited in China and many other countries. This study aimed to establish a surface-enhanced Raman spectroscopy (SERS) method for screening sodium metabisulfite residues on shrimp surfaces, in a non-destructive manner. The analysis was carried out using a portable Raman spectrometer jointly with copy paper loaded with silver nanoparticles as the substrate material. The SERS response of sodium metabisulfite gives two fingerprint peaks at 620 (strong) and 927 (medium) cm -1 , respectively. This enabled unambiguous confirmation of the targeted chemical. The sensitivity of the SERS detection method was determined to be 0.1 mg/mL, which was equal to residual sodium metabisulfite on the shrimp surface at 0.31 mg/kg. The quantitative relationship between the 620 cm -1 peak intensities and the concentrations of sodium metabisulfite was established. The linear fitting equation was y = 2375x + 8714 with R 2 = 0.985. Reaching an ideal balance in simplicity, sensitivity, and selectivity, this study demonstrates that the proposed method is ideally suitable for in-site and non-destructive screening of sodium metabisulfite residues in seafood.

In this work, we fabricated a novel origami paper-based analytical device (oPAD) assisted by the nanostructuring effect of in situ Pd decoration of Cu/Co-doped CeO 2 (CuCo-CeO 2 -Pd) nanospheres, functionalized with their strongly enhanced electrocatalytic properties to realize an electrochemical and visual signal readout system in oPAD, for highly sensitive detection of amyloid-β (Aβ). The CuCo-CeO 2 -Pd nanospheres were introduced as an enhanced "signal transducer layer" on account of the electron transfer acceleration caused by catalyzing glucose to produce H 2 O 2 for differential pulse voltammetry signal readout and further 3,3'5,5'-tetramethylbenzidine (TMB) oxidation for colorimetric analysis. Meanwhile, for achieving superior performance of the proposed oPAD, in situ growth of urchin-like gold nanoparticles (Au NPs) onto cellulose fibers was adopted to improve "the recognition layer" in favor of immobilizing antibodies for targeting Aβ through specific antigen-antibody interactions. Combined with the delicate design of oPAD, exhibiting actuation of the conversion procedure between hydrophobicity and hydrophilicity on paper tabs in the assay process, the oPAD successfully enabled sensitive diagnosis of Aβ in a linear range from 1.0 pM to 100 nM with a limit of detection of 0.05 pM (S/N = 3) for electrochemical detection, providing a reliable strategy for quantifying the Aβ protein in clinical applications.

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

The fast-growing healthcare demand for user-friendly and affordable analytical tools is driving the efforts to develop reliable platforms for the customization of therapy based on individual health conditions. In this overall scenario, we developed a paper-based electrochemical sensor for the quantification of iron ions in serum as a cost-effective sensing tool for the correct supplement administration. In detail, the working electrode of the screen-printed device has been modified with a nanocomposite constituted of carbon black and gold nanoparticles with a drop-casting procedure. Square wave voltammetry has been adopted as an electrochemical technique. This sensor was further modified with Nafion for iron quantification in serum after sample treatment with trifluoroacetic acid. Under optimized conditions, iron ions have been detected with a LOD down to 0.05 mg/L and a linearity up to 10 mg/L in standard solution. The obtained results have been compared with reference methods namely commercial colorimetric assay and atomic absorption spectroscopy, obtaining a good correlation within the experimental errors. These results demonstrated the suitability of the developed paper-based sensor for future applications in precision medicine of iron-deficiency diseases., (© 2023. Springer-Verlag GmbH Germany, part of Springer Nature.)

A dual-mode lab-on-paper device based on BiVO 4 /FeOOH nanocomposites as an efficient generating photoelectrochemical (PEC)/colorimetric signal reporter has been successfully constructed by integration of the lab-on-paper sensing platform and PEC/colorimetric detection technologies for sensitive detection of carcinoembryonic antigen (CEA). Concretely, the BiVO 4 /FeOOH nanocomposites were in situ synthesized onto the paper-working electrode (PWE) through hydrothermal synthesis of the BiVO 4 layer on cellulose fibers (paper-based BiVO 4 ) which were initially modified by Au nanoparticles for improving the conductivity of three dimensional PWE, and then the photo-electrodeposition of FeOOH onto the paper-based BiVO 4 to construct the paper-based BiVO 4 /FeOOH for the portable dual-mode lab-on-paper device. The obtained nanocomposites with an FeOOH needle-like structure deposited on the BiVO 4 layer exhibits enhanced PEC response activity due to its effective separation of the electron-hole pair which could further accelerate the PEC conversion efficiency during the sensing process. With the introduction of CEA targets onto the surface of nanocomposite-modified PWE assisted by the interaction with the CEA antibody from a specific recognition property, a signal-off PEC signal state with a remarkable photocurrent response decreasing trend can be achieved, realizing the quantitative detection of CEA with the PEC signal readout mode. By means of a smart origami paper folding, the colorimetric signal readout is achieved by catalyzing 3,3',5,5'-tetramethylbenzidine (TMB) to generate blue oxidized TMB in the presence of H 2 O 2 due to the satisfied enzyme-like catalytic activity of the needle-like structure, FeOOH, thereby achieving the dual-mode signal readout system for the proposed lab-on-paper device. Under the optimal conditions, the PEC and colorimetric signals measurement were effectively carried out, and the corresponding linear ranges were 0.001-200 ng·mL -1 and 0.5-100 ng·mL -1 separately, with the limit of detection of 0.0008 and 0.013 ng·mL -1 for each dual-mode. The prepared lab-on-paper device also presented a successful application in serum samples for the detection of CEA, providing a potential pathway for the sensitive detection of target biomarkers in clinical application.

Packaging is as important as the product itself because it is a crucial marketing and communication tool for business. Oxidized nanocellulose (ONC), extracted from agriculture residues of bagasse raw material using ecofriendly ammonium persulfate hydrolysis method, is used as support/reducing agent for the generation of silver nanoparticles (AgNPs) via photochemical procedure and reinforcing element in paper functionalization. The natural polymer, sodium alginate (SA) is exploited to enhance the binding of the ONC-AgNPs over cellulose fibers. The SA/ONC-AgNPs bio-nanocomposite is incorporated on paper matrix, which represents a more suitable choice respect to other substrates for its renewable, biocompatible, biodegradable, and cost-effective properties. Structural and antimicrobial evaluations show that the papers embedded with the SA/ONC-AgNPs possess good mechanical, thermal, barrier and antibacterial properties., Competing Interests: Declaration of competing interest There is no conflict of interest in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

In this work, the effect of using Ag-doped TiO 2 nanopigments on optical, mechanical and antimicrobial properties of coated paper was explored. Furthermore, the long-term antimicrobial activity of the coated paper was examined for up to 25 years. Titanium dioxide (TiO 2 ) nanoparticles have been synthesized and doped with different percentages of Ag nanoparticles (Ag NPs) using a simple wet chemical approach. The Ag@TiO 2 modified nanopigments were in the form of nanorods with an average size of about 20 nm as observed from TEM images. Increasing Ag content from 0.01 to 1.0% showed an increase in the mechanical properties of coated paper in terms of tensile, stretching, tensile energy absorption and burst while preserving the optical properties. Moreover, the antimicrobial inhibition activity increased with increasing the Ag content. The 1% Ag@TiO 2 showed a long-lasting antimicrobial effect against Staphylococcus aureus (S. aureus) Gram-positive bacteria even after 25 years of ageing (93.4% inhibition). Investigation of reactive oxygen species (ROS) generation and reaction mechanism of antimicrobial activity over Ag/TiO 2 under visible light is proposed. These results suggest that Ag/TiO 2 NPs can be potentially used as a disinfection coating for paper and improving its mechanical properties., (© 2022. The Author(s).)

A novel strategy is presented for simple, sensitive and selective branched-chain amino acids (BCAAs) detection in edible insects on a paper test strip device readout with a smartphone. Silver nanoparticles (AgNPs) were applied, interacting with dye, which provided 1.5 times higher color intensity than the one without AgNPs. The proposed paper test strip exhibiting the detection limit of leucine, isoleucine and valine were 6.0, 6.2 and 7.2 mg/L, respectively. The linear dynamic ranges were 20-120 mg/L for leucine and 20-110 mg/L for isoleucine and valine detections. The proposed paper test strip was successfully applied for the detection of BCAAs in edible insects. The analytical results obtained using paper test strips were in good agreement with those obtained via a commercial test kit. This study shows the successful integration of the paper test strip and the smartphone to afford an easy-to-use, inexpensive and portable device alternative for BCAAs analysis., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

The continuous intake of diethylstilbestrol (DES) residue seriously threatens the health of consumers, so the rapid and sensitive detection of DES is helpful for timely food safety warning. In this study, a photothermal-sensing microfluidic paper-based analytical chip (PT-Chip) was developed for effectively screening of DES residue in foods. Competitive inhibition immunochromatography was introduced and the composite of black phosphorus nanosheets and gold nanoparticles (BP-Au) was used as signal indicators. Then, the test area was irradiated by an 808 nm laser and the photothermal transduction signal was recorded by a thermal imager to achieve sensitive photothermal detection. The amount of DES was obtained by analyzing the temperature change curve of test area. The PT-Chip can achieve accurate quantification of DES with a detection limit of 0.1 μg/L. And the successful determination of DES in different food samples indicating that the PT-Chip can be used as a promising detection device., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)