Graphitic Carbon Nitride as an Amplification Platform on an Electrochemical Paper-Based Device for the Detection of Norovirus-Specific DNA.

Norovirus is one of the leading causes of gastroenteritis, acute vomiting, intense diarrhoea, acute pain in the stomach, high fever, headaches, and body pain. Conventional methods of detection gave us very promising results but had disadvantages such as low sensitivity, cost ineffectiveness, reduced specificity and selectivity, etc. Therefore, biosensors can be a viable alternative device which can overcome all setbacks associated with the conventional method. An electrochemical sensor based on oxidized graphitic carbon nitride (Ox-g-C3N4) modified electrochemical paper-based analytical device (ePAD) was fabricated for the detection of norovirus DNA. The synthesized Ox-g-C3N4 nanosheets were characterized by field emission scanning electron microscopy (FESEM), X-ray Diffraction (XRD), UV-Vis spectroscopy and X-Ray Photoelectron Spectroscopy. The capture probe DNA (PDNA) modified electrodes were characterized by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). These two characterization techniques were also employed to find the optimal scan rate, response time and temperature of the fabricated sensor. The fabricated biosensor showed a limit of detection (LOD) of 100 fM. Furthermore, the specificity of the reported biosensor was affirmed by testing the response of capture probe DNA with oxidized graphitic carbon nitride (PDNA/Ox-g-C3N4) modified ePAD on the introduction of a non-complimentary DNA. The fabricated ePAD sensor is easy to fabricate, cost effective and specific, and requires a minimum analysis time of 5 s.

Paper-Based Electrodes Conjugated with Tungsten Disulfide Nanostructure and Aptamer for Impedimetric Detection of Listeria monocytogenes.

In this study, we report on a novel aptasensor based on an electrochemical paper-based analytical device (ePAD) that employs a tungsten disulfide (WS2)/aptamer hybrid for the detection of Listeria monocytogenes. Listeria is a well-known causative pathogen for foodborne diseases. The proposed aptasensor signifies many lucrative features which include simple, cost-effective, reliable, and disposable. Furthermore, the use of an aptamer added more advantageous features in the biosensor. The morphological, optical, elemental composition, and phase properties of the synthesized tungsten disulfide (WS2) nanostructures were characterized by field-emission scanning electron microscopy (FESEM), RAMAN spectroscopy, photoluminescence (PL), and X-ray diffraction (XRD), while electrochemical impedance spectroscopy was performed to corroborate the immobilization of aptamer and to assess the L. monocytogenes sensing performance. The limit of detection (LoD) and limit of quantification (LoQ) of the aptasensor was found to be 10 and 4.5 CFU/mL, respectively, within a linear range of 101-108 CFU/mL. The proposed sensor was found to be selective solely towards Listeria monocytogenes in the presence of various bacterial species such as Escherichia coli and Bacillus subtilis. Validation of the aptasensor operation was also evaluated in real samples by spiking them with fixed concentrations (101, 103, and 105) of Listeria monocytogenes, thereby, paving the way for its potential in a point-of-care scenario.

Graphene Based Electrochemical DNA Biosensor for Detection of False Smut of Rice (Ustilaginoidea virens).

False smut caused by Ustilaginoidea virens is an important rice fungal disease that significantly decreases its production. In the recent past, conventional methods have been developed for its detection that is time-consuming and need high-cost equipments. The research and development in nanotechnology have made it possible to assemble efficient recognition interfaces in biosensors. In this study, we present a simple, sensitive, and selective oxidized graphene-based geno-biosensor for the detection of rice false smut. The biosensor has been developed using a probe DNA as a biological recognition element on paper electrodes, and oxidized graphene to enhance the limit of detection and sensitivity of the sensor. Probe single-stranded DNA (ssDNA) and target ssDNA hybridization on the interface surface has been quantitatively measured with the electrochemical analysis tools namely, cyclic voltammetry, and linear sweep voltammetry. To confirm the selectivity of the device, probe hybridization with non-complementary ssDNA target has been studied. In our study, the developed sensor was able to detect up to 10 fM of target ssDNA. The paper electrodes were employed to produce an effective and cost-effective platform for the immobilization of the DNA and can be extended to design low-cost biosensors for the detection of the other plant pathogens.

Self-Assembled Two-Dimensional Molybdenum Disulfide Nanosheet Geno-Interface for the Detection of Salmonella.

This report presents a novel lab-on-a-paper (LoP)-based device coupled with a molybdenum disulfide nanosheet (MoS2NS)-modified electrochemical genosensor for detecting Salmonella-specific DNA. Conductive electrodes were grafted on a paper-based substrate employing a stencil printing technique, and MoS2NS was decorated on the working electrode. MoS2NS has strong affinity toward nucleo bases, which made it a best sensing interface for the immobilization of DNA. Morphological, optical, and structural characterizations were accomplished using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), UV-vis spectroscopy (UV-vis), and Raman spectroscopy, repectively. The current studies of an electrochemical genosensor demonstrated a good linear detection range from 100-20 nM and a low limit of detection of 20 nM toward Salmonella DNA with R 2 = 0.991. The proposed LoP-based genosensor confirmed as a better sensing podium and an effectual immobilization matrix for DNA.

Morphology-Preferable MoSe2 Nanobrooms as a Sensing Platform for Highly Selective Apta-Capturing of Salmonella Bacteria.

The present report employed nanobroom (NB)-shaped two-dimensional molybdenum diselenide (MoSe2) for the preparation of a sensing matrix for the detection of Salmonella paratyphi. An aptamer specific to salmonella was immobilized onto MoSe2NB-modified fluorine-doped tin oxide via glutaraldehyde cross-linking. Structural and morphological characterizations were performed using UV-vis spectroscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction techniques. Characterizations confirmed the nanobroom morphology and nanosize of the MoSe2 material. Electrochemical studies revealed a good linear detection range of 10-2-10-10 CFU/mL with low detection limit of 1 × 10-10 CFU/mL and with R 2 = 0.98. The developed preferable nanobroom-shaped sensing matrix can provide a promising platform for rapid and accurate detection of Salmonella in real samples due to its tremendous stability and sensitivity.

Ultrasensitive electrochemical immuno-sensing platform based on gold nanoparticles triggering chlorpyrifos detection in fruits and vegetables.

Chlorpyrifos (chl) is an organophosphate pesticide extensively used in agriculture and highly toxic for human health. Fluorine doped tin-oxide (FTO) based electrochemical nanosensor was developed for chlorpyrifos detection with gold nanoparticles (AuNPs) and anti-chlorpyrifos antibodies (chl-Ab). AuNPs provides high electrical conductivity and specific resistivity, thus increases the sensitivity of immunoassay. High electrical conductivity of AuNPs reveals that it promotes the redox reaction for better cyclic voltammetry. Based on the intrinsic conductive properties of FTO-AuNPs complex, chl-Ab was immobilized onto AuNPs surface. Under optimized conditions, the proposed FTO based nanosensor exhibited high sensitivity and stable response for the detection of chlorpyrifos, ranging from 1fM to 1µM with limit of detection (LOD) up to 10fM. The FTO-AuNPs sensor was successfully employed for the detection of chlorpyrifos in standard as well in real samples up to 10nM for apple and cabbage, 50nM for pomegranate. The proposed FTO-AuNPs nanosensor can be used as a quantitative tool for rapid, on-site detection of chlorpyrifos traces in real samples when miniaturized due to its excellent stability, sensitivity, and simplicity.

Development of MoSe2 Nano-Urchins as a Sensing Platform for a Selective Bio-Capturing of Escherichia. coli Shiga Toxin DNA.

The present study was aimed to develop "fluorine doped" tin oxide glass electrode with a MoSe2 nano-urchin based electrochemical biosensor for detection of Escherichia. coli Shiga toxin DNA. The study comprises two conductive electrodes, and the working electrodes were drop deposited using MoSe2 nano-urchin, and DNA sequences specific to Shiga toxin Escherichia. coli. Morphological characterizations were performed using Fourier transforms infrared spectrophotometer; X-ray diffraction technique and scanning electron microscopy. All measurements were done using methylene blue as an electrochemical indicator. The proposed electrochemical geno-sensor showed good linear detection range of 1 fM⁻100 µM with a low detection limit of 1 fM where the current response increased linearly with Escherichia. coli Shiga toxin dsDNA concentration with R2 = 0.99. Additionally, the real sample was spiked with the dsDNA that shows insignificant interference. The results revealed that the developed sensing platform significantly improved the sensitivity and can provide a promising platform for effective detection of biomolecules using minute samples due to its stability and sensitivity.