Stable gold nanoparticles as a novel peroxidase mimic for colorimetric detection of cysteine

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Abstract
In this work, a novel method for colorimetric detection of cysteine was proposed based on the inhibition of peroxidase-like behavior of AuNPs. Kiwi juice prepared gold nanoparticles presented strong catalytic activity, which could catalyze H2O2–TMB to generate a blue product, resulting in strong absorption at 650 nm. In HAc–NaAc (pH 4.0) buffer, cysteine induced the aggregation of gold nanoparticles through covalent Au–S bonds and electrostatic as well as hydrogen bonding, leading to the reduction of the catalytic activity of gold nanoparticles with a weakened blue color product and a lower absorbance. Under optimal conditions, the concentrations of cysteine were proportional to the degree of reduced absorbance. This approach offers a new, simple, sensitive and selective assay for cysteine.

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