Selective turn-on fluorescence assay of 6-thioguanine by using harmine-modified silver nanoparticles.

This article reports on a novel fluorescence resonance energy transfer (FRET) system between harmine and silver nanoparticles (AgNPs), in which harmine acts as the donor and AgNPs act as the acceptor. As a result of FRET, harmine fluorescence is quenched efficiently with a corresponding Stern-Volmer constant of 3.61 × 10(11)  L/mol. It was found that upon addition of the anticancer drug, 6-thioguanine (6-TG), the fluorescence was recovered due to the competitive adsorption of this compound onto AgNPs. Based on this effect, a selective turn-on fluorescence sensor was developed for the determination of 6-TG. Under optimum conditions, the enhanced fluorescence intensity displays a linear relationship with the concentration of 6-TG in the range 1.5 × 10(-8) -7.5 × 10(-7)  M with a detection limit of 9.7 nM. The developed method was applied to the determination of this drug in a pharmaceutical preparation and human plasma samples.