Colorimetric detection of mercury ion (Hg2+) based on DNA oligonucleotides and unmodified gold nanoparticles sensing system with a tunable detection range

Here, we report a simple and sensitive colorimetric detection method for Hg2+ ions with a tunable detection range based on DNA oligonucleotides and unmodified gold nanoparticles (DNA/AuNPs) sensing system. Complementary DNA strands with T–T mismatches could effectively protect AuNPs from salt-induced aggregation. While in the presence of Hg2+ ions T–Hg2+–T coordination chemistry leads to the formation of DNA duplexes, and AuNPs are less well protected thus aggregate at the same salt concentration, accompanying by color change from red to blue. By rationally varying the number of T–T mismatches in DNA oligonucleotides, the detection range could be tuned. Employing duplex oligonucleotides with 4 T–T mismatches in the sensing system, a sensitive linear range for Hg2+ ions from 0 to 5 μM and a detection limit of 0.5 μM are obtained. Adding the number of T–T mismatches to 6 and 8, the assay region is enlarged and linear range is tuned. A low proportion of T–T mismatches makes the detection range narrow but the sensitivity high while a high proportion influences the detection limit but enlarges assay region. Besides, the sensor also shows a good selectivity for Hg2+.