DNA based gold nanoparticles colorimetric sensors for sensitive and selective detection of Ag(I) ions

In this work, we reported both unlabeled and labeled sensing strategies for Ag(I) ions detection by using the DNA based gold nanoparticles (AuNPs) colorimetric method. In the unlabeled strategy, C-base riched single strand DNA (C-ssDNA) enwinded onto AuNPs to form AuNPs/C-ssDNA complex. In the labeled method, sulfhydryl group modified C-ssDNA (HS-C-ssDNA) was covalently labeled on AuNPs to produce AuNPs-S-C-ssDNA complex. In both strategies, C-ssDNA or HS-C-ssDNA could enhance the AuNPs stability against the salt-induced aggregation. However, the presence of Ag(I) ions in the obtained AuNPs/C-ssDNA or AuNPs-S-C-ssDNA complex would decrease such stability to display purple even blue colors due to the formation of Ag(I) ions mediated C-Ag(I)-C base pairs. Through this phenomenon, Ag(I) ions could be detected qualitatively and quantitatively using both unlabeled and labeled sensing strategies. Compared with the labeled method, the unlabeled strategy avoided the label and separation steps in common sensors, which may thus save both the time and cost for the detection. Nevertheless, the labeled strategy provided more sensitive, stable and controllable sensing results compared with the unlabeled method. By the labeled strategy, 12 nM Ag(I) ions could be observed directly by naked eyes, and the lowest detectable concentration of 0.59 nM was gotten under by the UV–vis spectra measurement, which was one of the most sensitive results among DNA based AuNPs colorimetric sensors for metal ions.