Utility of biopolymer [poly(L-Cysteine)] modified glassy carbon electrode for the determination of Ponceau 4R (P4R), a food colorant, was explored during the present study. On the probe [poly(L-Cys)/GCE], P4R behaved as perfectly reversible redox system with E pa = 0.031 V and E pc = −0.001 V ( E p = 0.032 V). Significant decrease in the oxidation potential and remarkable increase in the current response of P4R on biopolymer modified GCE attests the excellent electron transfer capacity of the modified electrode towards the oxidation of P4R. Under optimal conditions, anodic peak current of P4R showed a linear behavior in the range 1.0 × 10 −5 to 1.0 × 10 −6 M, with minimum detectable concentration of 3.73 × 10 −8 M. Kinetic parameters viz., charge transfer coefficient (α) and heterogeneous rate constant (k s ) have also been determined. Chronocoulometry was employed to calculate saturated adsorption capacity and diffusion coefficient (D) and values obtained were 5.54 × 10 −9 mol cm −2 and 2.93 × 10 −6 cm 2 s −1 , respectively. Applicability of designed sensor was demonstrated in commercial soft drink samples.
Glutathione is an important antioxidant found in body fluids and tissues, which inhibit damage to essential cellular constituents caused by reactive oxygen species. The analysis of glutathione levels in biological systems is important in early clinical diagnosis. A novel, cost-effective synthetic strategy has been developed for the fluorescent probe ethylenediamine passivated carbon dots. Tissue paper was chosen as the carbon source for this "green one pot" synthesis. Glutathione could induce quenching of the fluorescence intensity of ethylenediamine passivated carbon dots through surface interactions, resulting from their aggregation. Based on this, a novel fluorescence sensor was fabricated for the determination of Glutathione in body fluids. A linear calibration graph was obtained in the range of 6.0 × 10 -7 to 5.0 × 10 -8 M with a detection limit of 1.74 × 10 -9 M. The developed sensor was successfully used for the determination of glutathione in artificial saliva samples.
Fluorescence quenching behavior of artificial food colorant quinoline yellow (QY), on interaction with L-cysteine stabilized copper nanoclusters (L-Cys-CuNCs) is investigated in this work. For this purpose, L-cysteine stabilized CuNCs were synthesized and characterized using various analytical techniques. Results demonstrated that the synthesized probe (size~2 nm) had very promising optical features such as bright blue fluorescence, significant quantum yield and excellent photostability. L-Cys-CuNCs can function as a fluorescence sensor by selectively sensing QY among other yellow colorants, giving a detection limit as low as 0.11 μM. The developed sensor exhibited a linear concentration range from 5.50 to 0.20 μM. The developed fluorescence assay was successfully applied for testing commercial samples, thereby making this sensing strategy significant for quality control of food stuffs.
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