Construction of FRET biosensor for off-on detection of lead ions based on carbon dots and gold nanorods.

Exploring new energy donor/acceptor pairs for constructing FRET system has important research significance. In this study, a FRET assembly by using carbon dots (CDs) as energy donor and gold nanorods (Au NRs) as energy acceptor has been proposed through covalent bond interactions by taking advantage of cysteamine as a bridge. The assembly is characterized by UV-vis absorption spectra, fluorescence spectra, FT-IR spectra and TEM images, revealing that Au NRs successfully absorbed on the surface of CDs. As for the occurrence of FRET process from CDs to Au NRs, the fluorescence signal of CDs-cysteamine-Au NRs assembly quenched significantly. Interestingly, Pb2+ ions could bind completely with cysteamine and disturbed the FRET process, which activated fluorescence signal of the system. Based on these experimental phenomena, CDs-cysteamine-Au NRs assembly was performed as an off-on FRET biosensor for Pb2+ ions. The linear range obtained is from 0 to 155 μM with the detection limit of 0.05 μM. Moreover, the FRET-based sensor exhibited high selectivity to the analyte Pb2+ ions against other interference substances. Furthermore, the present approach was successfully applied to detect Pb2+ ions in real samples, which suggested its potential applications in environmental monitoring.