DNA-functionalization gold nanoparticles based fluorescence sensor for sensitive detection of Hg2+ in aqueous solution

• The sensor was optimized with the modification of the “helper” oligonucleotides.
• The sensor shows high selectivity for Hg2+ in the presence of other metal ions.
• The limit of detection is as low as 8 nmol l−1.
• The sensor was successfully employed to determine Hg2+ in tap water samples.

We have developed a sensitive, selective, and simple fluorescence spectrometric sensor for Hg2+ detection in aqueous solution by using thiol-DNA-functionalized gold nanoparticles (Au NPs). This sensor is based on the Hg2+-induced conformational change of single-stranded DNA (ssDNA) with an enhanced fluorescence resonance energy transfer (FRET) process between the energy donor (fluorescein, FAM) and the energy acceptor (Au NPs). In the presence of Hg2+, a formation of a hairpin structure for ssDNA originates from thymine-Hg2+-thymine (T-Hg2+-T) coordination, resulting in notable fluorescence quenching in comparison to the random coil. In order to improve the stability and sensitivity of the sensor, we adopt short “helper” oligonucleotides to increase the density of DNA on the surface of Au NPs. The assay enables the detection limit for the detection of Hg2+ is 8 nM, and is extremely specific for Hg2+ even in the presence of high concentrations of other metal ions. Toward the goal for practical applications, this sensor was applied to monitor Hg2+ in tap water samples and showed low matrix interference and high sensitivity.

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