Highly sensitive and selective detection of trinitrotoluene using cysteine-capped gold nanoparticles

Trinitrotoluene (TNT), being an electron deficient species, can easily bind with electron rich amine groups and form a specific charge transfer Jackson-Meisenheimer (JM) complex. In the present study, we report the formation of a JM complex using cysteine capped gold nanoparticles in the presence of TNT. Sodium citrate is used as reducing agent for the synthesis of gold nanoparticles in an aqueous dispersion. The as synthesized gold nanoparticles are capped with L-cysteine (Au@Cys), an amino acid possessing an additional thiol functional group besides the alpha-amine. The interaction of gold nanoparticles with cysteine in the presence of TNT (AuCys@TNT) is investigated using UV-vis spectroscopy, Raman spectroscopy, FTIR spectroscopy and TEM. A possible model for cysteine binding to gold nanoparticles and the formation of the JM complex, leading to the ultra-trace detection of TNT up to 1 ppb with good reproducibility (n = 3), is also suggested.