Enhancement in sensitivity of fluorescence based assay for organophosphates detection by silica coated silver nanoparticles using organophosphate hydrolase

The aim of the present work is to enhance the sensitivity of the fluorescence based developed detection assay for the estimation of organophosphates by exploiting the spectral property of metal enhanced fluorescence shown by silver nanoparticles. The receptor entity consisted of organophosphorus hydrolase with a histidine tail (OPH6His) at its C terminus which has been conjugated to pH sensitive high quantum yield fluorophore i-e pyranine (8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt). The introduction of silica nanoshell (∼30 nm) on silver nanoparticles (∼35 nm) ameliorated tuning of surface plasmon resonance wavelength of silver nanoparticles to the excitation wavelength of pyranine which ultimately led to a ten-fold increase in the fluorescence signal to that given by OPH6His–pyranine bioconjugate. This fluorescence enhancement resulted in lowering of detection limit from 20 ppb to 2 ppb for paraoxon and 50 ppb to 10 ppb for methyl parathion.