A colorimetric silver nanoparticle-based assay for Hg(II) using lysine as a particle-linking reagent

We describe a colorimetric method for the determination of Hg(II) that is based on the aggregation of silver nanoparticles (AgNPs) in the presence of Hg(II) and lysine. If Hg(II) ions are added to unmodified AgNPs, they will deposit on the surface where they will be reduced to Hg(0) by NaBH4 to form a shell around the AgNPs. Upon addition of lysine to the Hg(II)-capped AgNPs, the aggregation of the AgNPs will be induced because the two amino groups of lysine have a high affinity for Hg(II). Aggregation results in a color change from orange to yellowish. The effect was exploited to design a colorimetric assay for Hg(II) that has a 1 nM detection limit.