Silver nanoparticle-supported hydroxyapatite as a material for visual detection of urinary cysteine†
A new approach for colorimetric detection of cysteine in a 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 from samples and the 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 the 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 a percentage of recovery in the range of 94.4 to 102.8% was obtained.