A novel aptasensor based on single-molecule force spectroscopy for highly sensitive detection of mercury ions

Abstract

We have developed a novel aptasensor based on single-molecule force spectroscopy (SMFS) capable of detecting mercury ions (Hg²⁺) with sub-nM sensitivity. The single-strand (ss) DNA aptamer used in this work is rich in thymine (T) and readily forms T–Hg²⁺–T complexes in the presence of Hg²⁺. The aptamer was conjugated to an atomic force microscope (AFM) probe, and the adhesion force between the probe and a flat graphite surface was measured by single-molecule force spectroscopy (SMFS). The presence of Hg²⁺ ions above a concentration threshold corresponding to the affinity constant of the ions for the aptamer (about 5 × 10⁹ M⁻¹) could be easily detected by a change of the measured adhesion force. With our chosen aptamer, we could reach an Hg²⁺ detection limit of 100 pM, which is well below the maximum allowable level of Hg²⁺ in drinking water. In addition, this aptasensor presents a very high selectivity for Hg²⁺ over other metal cations, such as K⁺, Ca²⁺, Zn²⁺, Fe²⁺, and Cd²⁺. Furthermore, the effects of the ionic strength and loading rate on the Hg²⁺ detection were evaluated. Its simplicity, reproducibility, high selectivity and sensitivity make our SMFS-based aptasensor advantageous with respect to other current Hg²⁺ sensing methods. It is expected that our strategy can be exploited for monitoring the pollution of water environments and the safety of potentially contaminated food.