Highly sensitive surface acoustic wave biosensor for the detection of Hg2+ based on the thymine–Hg2+–thymine structure

Abstract

The detection of mercury ions (Hg²⁺) with an ultralow concentration is of great significance for the treatment of heavy metal pollution in industrial waste water and the monitoring of drinking water quality. In this study, a simple, sensitive, and portable surface acoustic wave (SAW) biosensor for the determination of Hg²⁺ concentration was developed. First, a DNA fragment with a specific binding capacity for Hg²⁺ was chemically adsorbed on to the sensitive region through forming Au–S bonds with the SAW biosensor. The DNA probe could then form a thymine–Hg²⁺–thymine (T–Hg²⁺–T) complex with strong affinity for Hg²⁺ after immersion in a test solution containing Hg²⁺, resulting in a significant change in the response frequency of the device. The linear detection range of the device was 10 pM to 1 nM, while the limit of detection (LOD) was as low as 6.3 pM. Furthermore, the SAW biosensor exhibited excellent selectivity to Hg²⁺ compared with that of interfering ions, e.g., Ag⁺, Ba²⁺, Cu²⁺, Zn²⁺, Mn²⁺, Fe³⁺, Ca²⁺, and Na⁺. The results provide a new strategy for the preparation of portable devices that can monitor toxic heavy metal ions with high sensitivity and selectivity.