Ultrasensitive and highly selective FRET aptasensor for Hg2+ measurement in fish samples using carbon dots/AuNPs as donor/acceptor platform

In this study, a novel fluorescence resonance energy transfer (FRET) aptasensor for detection of Hg2+ ions in real samples is described. The sensor is based on single-stranded DNA (ssDNA)-modified carbon dots (CDs) as an energy donor and complementary DNA (cDNA)-modified Au nanoparticles (AuNPs) as an energy acceptor. The CDs were synthesized by the hydrothermal reaction of histidine. The resulting CDs were conjugated with ssDNA through amidation reaction. The AuNPs-cDNA sample was prepared by self-immobilization of thiolated cDNA on the surface of Au nanoparticles. Specific hybridization between ssDNA and cDNA was achieved by mixing CDs-ssDNA and AuNPs-cDNA. The result of this phenomenon is quenching of the fluorescence associated with the FRET process. The response of the aptasensor was based on selective interaction of Hg2+ ions with thymine (T) groups in CDs-ssDNA, which led to displacement of AuNPs-cDNA by Hg2+ and an increase in fluorescence intensity. The aptasensor could be used in the range from 1.3 × 10−12 to 2.4 × 10−5 M for Hg2+ ions with a detection limit of 7.5 × 10−13 M. It showed high selectivity for Hg2+ with respect to several common metal ions. This aptasensor has been used for the determination of mercury ion concentration in fish samples.