Cysteine-stabilized silver nanoparticles as a colorimetric probe for the selective detection of cysteamine.

The purpose of the present research was to design a method for the colorimetric determination of cysteamine. We have employed cysteine-stabilized silver nanoparticles (AgNPs) as a probe. The addition of cysteamine resulted in the quenching of the 400 nm surface plasmon resonance (SPR) band of the AgNPs. It was accompanied by the appearance of a new absorption band at 560 nm. The colour of the colloidal AgNPs changed from yellow to dark brown within a few seconds. The change in colour of the AgNPs was due to their aggregation induced by the addition of cysteamine. Significantly, other biomolecules such as arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutathione, glycine, methionine and 6-mercaptopurine did not cause any change in the colour of the AgNPs. The limit of detection (LOD) of the method was 0.37 μM. The mechanism of the aggregation of the AgNPs induced by cysteamine has also been described. The method has been applied for the detection of cysteamine in human blood serum.