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Radical scavenging efficacy of L-cysteine (L-Cys), glutathione (GSH) and thioctic acid (TA) in the presence of silver nanoparticles (AgNPs) were determined by 1,1-diphenyl 2-picryl hydrazil (DPPH), nitric oxide (NO) and hydroxyl (OH) radicals as spectrophotometric assay. The hydrogen peroxide (H 2 O 2) scavenging efficacy has been determined by titration method. Ascorbic acid has been used as standard for all radical scavenging efficacies. In general, antioxidant activity decreases in the presence of AgNPs. The covalent interactions of thiols (-SH) were found to be a key factor for the decreases in scavenging activity. The effect of thiol concentrations has been discussed. The size and shape of the nanoparticles and AgNP-SR interactions have been characterized through Transmission Electron Microscopy (TEM) and Fourier Transform Infrared (FTIR) spectroscopy, respectively.

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Arsenic (As) is a hazardous and ubiquitous element; hence the quantitative detection of arsenic in various kinds of environmental sample is an important issue. Herein, we reported L-cysteine capped CdTe Quantum dot based optical sensor for the fluorometric detection of arsenic (III) in real water sample. The method is based on the fluorescence quenching of QDs with the addition of arsenic solution that caused the reduction in fluorescence intensity due to strong interaction between As and L-cysteine to form As(Cys). The calibration curve was linear over 2.0 nM-0.5 μM arsenic with limit of detection (LOD) of 2.0 nM, correlation coefficient (r) of 0.9698, and relative standard deviation (RSD %) of 5.2%. The Stern-Volmer constant for the quenching of CdTe QDs with As at optimized condition was evaluated to be 1.17 × 10 L mol s. The feasibility of the sensor has been analyzed by checking the inference of common metal ions available in the water such as K, Na, Mg, Ca, Ba, Cu, Ni, Zn, Al, Co, Cr, Fe and its higher oxidation state As. Graphical Abstract Schematic representation of As detection by L-Cysteine capped CdTe QDs.

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