A simple green route to prepare stable silver nanoparticles with pear juice and a new selective colorimetric method for detection of cysteine

Abstract

In this work, a new cost-effective, rapid and simple method for the preparation of stable silver nanoparticles (AgNPs) was developed, which can be completed within 15 minutes at room temperature by oxidizing the reductants in pear juice with AgNO₃. Compared with the most used citrate-capped AgNPs, the as-prepared AgNPs showed high stability, good biocompatibility and enhanced antibacterial activity. Based on the formation of Ag–S covalent bonds between cysteine and AgNPs as well as the electrostatic interaction of COO⁻ and NH₄⁺ between cysteine molecules, which selectively lead to the aggregation of the as-prepared AgNPs and give a specific yellow-to-red colour change, a new selective colorimetric method for detection of cysteine was proposed with the as-prepared AgNPs by coupling the decrease of the characteristic localized surface plasmon resonance (LSPR) absorption at 406 nm of the as-prepared AgNPs and the increase of the new aggregation-induced band at 530 nm. The ratio of the absorbance at 530 nm to 406 nm (A₅₃₀/A₄₀₆) was found to be linearly dependent on the cysteine concentrations in the range of 5.0 × 10⁻⁷ to 1.0 × 10⁻⁵ M with a limit of detection of 6.8 × 10⁻⁸ M.