Colorimetric Detection of Hg2+ Based on the Growth of Aptamer-Coated AuNPs: The Effect of Prolonging Aptamer Strands.

Herein, a versatile and sensitive colorimetric sensor for Hg2+ based on aptamer-target specific binding and target-mediated growth of AuNPs is reported. The 15 T bases are first designed to detect Hg2+ through T-Hg2+ -T coordination. Aptamer-target binding results in the desorption of the aptamer from AuNP surface, the remaining aptamers adsorbed on AuNP surface trigger the growth of AuNPs with morphologically varied nanostructures, and then different colored solutions are formed. On this occasion, the limit of detection (LOD) of 9.6 × 10-9 m is obtained. The other two aptamer strands (25- and 59-mer) are designed by increasing A bases on either side and both sides of 15 T, respectively. The interaction of the binding domain and Hg2+ makes desorption of 15 T from AuNP surface, whereas excess bases not committed to the binding domain still adsorbed on AuNP surface. These excess bases control the growth of AuNPs, and enhance the sensitivity. The LODs are 4.05 and 3 × 10-9 m for 25- and 59-mer aptamers, respectively. In addition, the 59-mer aptamer system is applied to identify Hg2+ in real river samples, the LOD of 6.2 × 10-9 m is obtained.