Silver Nanoparticle-Supported Hydroxyapatite as Material for Visual Detection of Urinary Cysteine
A new approach for colorimetric detection of cysteine in urine sample has been established based on the aggregations of silver nanoparticles (AgNPs) on hydroxyapatite (HAp). The silver ion-modified hydroxyapatite (Ag-HAp) via ion-exchange was used to extract cysteine in samples and a formation of AgNPs, confirmed by Transmission Electron Microscopy (TEM), occurred after NaBH4 treatment. Different cluster sizes of AgNPs on HAp resulting from various amounts of cysteine induced a color change from yellow to pink or violet as concentration of cysteine increased. The linear range for cysteine determination was in the range of 0-105 µM with a detection limit of 2.03 µM. Sample pretreatment and standard addition allowed detection of cysteine in urine samples, and the percentage of recovery in the range of 94.4 to 102.8 % was obtained.