Glutathione-capped CuO nanoparticles for the determination of cystine using resonance Rayleigh scattering spectroscopy.

Ascorbic acid was used to reduce cystine to cysteine that induces the aggregation of glutathione-capped copper oxide nanoparticles. The aggregation of CuO NPs was optimized through resonance Rayleigh scattering and dynamic light scattering measurements. The high specificity toward cysteine from other amino acids and biomolecules was due to its mercapto group that binds to the surface of CuO NPs and the electrostatic interaction between the cysteine zwitterions on the surface of CuO NPs. Accordingly, glutathione-capped copper oxide nanoparticles was used as a sensing probe for cystine based on resonance Rayleigh scattering (RRS) technique. Increase in the RRS signal of CuO NPs was observed with increasing cystine concentration. A linear calibration plot was obtained in the range 2-20 μM with a limit of detection of 4.55 ± 0.5 nM, which is lower than literature value. The applicability of the proposed sensing strategy toward cystine was established, and the recovery percentage was between 99.8 ± 0.4 and 101.0 ± 2.1 for n = 3. Graphical Abstract .