Aggregation-aided SERS: Selective detection of arsenic by surface-enhanced Raman spectroscopy facilitated by colloid cross-linking.

Arsenic of natural or industrial origin often occurs in water and makes it impotable. Due to its high toxicity, very sensitive detection is required. In the present study an ultra-sensitive arsenite (As) sensing is reported, based on aggregation-aided surface-enhanced Raman scattering (AA-SERS) of modified silver colloids. SERS intensity of mercapto-compounds attached to the colloidal silver nanoparticles surface is greatly increased in the presence of arsenic. Colloid aggregation is facilitated by cross-linking; a meshwork consisting of arsenic atoms and glutathione bridges is formed, as indicated by UV-Vis absorption spectroscopy, TEM and Raman imaging. The best 2-mercaptopyridine reporter molecule makes it possible to directly detect As at concentrations as low as 0.5 ppb, which is better than achieved by the SERS technique so far.