A nucleic acid dye-enhanced electrochemical biosensor for the label-free detection of Hg based on a gold nanoparticle-modified disposable screen-printed electrode.

In this paper, a nucleic acid dye-enhanced electrochemical biosensor based on a screen-printed carbon electrode (SPCE) modified with Au nanoparticles (AuNPs) was designed for the detection of Hg in water. AuNPs were modified on the surface of the disposable SPCE through the electrodeposition of HAuCl. Subsequently, thiolated DNA probes were immobilized on the AuNP-modified electrode surface by Au-S reaction. After Hg was bound with a DNA probe by thymine (T)-Hg-thymine (T) mismatch, the DNA probe was folded into a hairpin structure where positively charged GelRed molecules were embedded into the double-stranded part of the hairpin. Thus, the current of [Fe(CN)] increased significantly on account of the decreased electrostatic repulsion at the electrode surface. Under the optimized experimental conditions, the peak current of [Fe(CN)] exhibited a good linear relationship with lgC in the concentration of Hg linear range of 0.1 nM to 500 nM, and the limit of detection (S/N = 3) was calculated as 0.04 nM. The electrochemical sensor also exhibited excellent selectivity for Hg in the presence of nine interfering ions, including Na, Fe, Ni, Mg, Co, Pb, K, Al and Cu. Meanwhile, the developed electrochemical sensor was tested in the analysis of Hg in tap water and river water samples, and the recoveries ranged from 81.0 to 114%. Therefore, this nucleic acid dye-enhanced electrochemical biosensor provided the advantages of simplicity, sensitivity, and specificity and is expected to be an alternative for Hg detection in actual environmental samples.