Shikha Wadhwa

Aloe vera assisted facile green synthesis of reduced graphene oxide for electrochemical and dye removal applications

In the present work, the suitability of Aloe vera (AV) as a ‘green reducing agent’ has been investigated for the reduction of graphene oxide (GO). The extent of reduction was studied by varying the amount of AV. The physical and chemical properties of the GO and reduced graphene oxide (rGO) were investigated using UV-Vis spectrophotometry, FT-IR spectroscopy, High Resolution Transmission Electron Microscopy (HRTEM) and Selected Area Electron Diffraction (SAED). Partially reduced graphene oxide sheets obtained with 7.5 g of AV (rGO-7.5) demonstrated a maximum reduction efficiency of about 73% as evident from FT-IR data. Cyclic voltammetry and electrochemical impedance spectroscopy studies revealed a significant enhancement in current density and a decrease in charge transfer resistance for the rGO-7.5 sample. Moreover, the as prepared rGO-7.5 sample showed a remarkable dye removal ability with a maximum efficiency of ∼98%. The enhanced surface area, π–π interaction and strong electrostatic attraction were correlated with the dye removal capability. The adsorption kinetics were also studied and pseudo second order adsorption phenomena were confirmed. The recyclability of the rGO-7.5 sample was further investigated and an excellent desorption capability was established.

A new tactics for the detection of S. aureus via paper based geno-interface incorporated with graphene nano dots and zeolites

Staphylococcus aureus (S. aureus) is a pathogenic bacteria which causes infectious diseases and food poisoning. Current diagnostic methods for infectious disease require sophisticated instruments, long analysis time and expensive reagents which restrict their application in resource-limited settings. Electrochemical paper based analytical device (EPAD) was developed by integrating graphene nano dots (GNDs) and zeolite (Zeo) using specific DNA probe. The ssDNA/GNDs-Zeo modified paper based analytical device (PAD) was characterized using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The genosensor was optimized at pH7.4 and incubation temperature of 30°C. A linear current response with respect to target DNA concentrations was obtained. The limit of detection (LOD) of the proposed sensor was found out to be 0.1nM. The specificity was confirmed by introducing non-complimentary target DNA to ssDNA/GNDs-Zeo modified PAD. The suitability of the proposed EPAD genosensor was demonstrated with fruit juice samples mixed with S. aureus. The proposed EPAD genosensor is a low cost, highly specific, easy to fabricate diagnostic device for detection of S. aureus bacteria which requires very low sample volume and minimum analysis time of 10s.

Comparative analysis of single-walled and multi-walled carbon nanotubes for electrochemical sensing of glucose on gold printed circuit boards

In the present work, a comparative study was performed between single-walled carbon nanotubes and multi-walled carbon nanotubes coated gold printed circuit board electrodes for glucose detection. Various characterization techniques were demonstrated in order to compare the modified electrodes viz. cyclic voltammetry, electrochemical impedance spectroscopy and chrono-amperometry. Results revealed that single-walled carbon nanotubes outperformed multi-walled carbon nanotubes and proved to be a better sensing interface for glucose detection. The single-walled carbon nanotubes coated gold printed circuit board electrodes showed a wide linear sensing range (1 mM to 100 mM) with detection limit of 0.1 mM with response time of 5 s while multi-walled carbon nanotubes coated printed circuit board gold electrodes showed linear sensing range (1 mM to 100 mM) with detection limit of 0.1 mM with response time of 5 s. This work provided low cost sensors with enhanced sensitivity, fast response time and reliable results for glucose detection which increased the affordability of such tests in remote areas. In addition, the comparative results confirmed that single-walled carbon nanotubes modified electrodes can be exploited for better amplification signal as compared to multi-walled carbon nanotubes.

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.