Visual detection of Hg²⁺ in aqueous solution using gold nanoparticles and thymine-rich hairpin DNA probes

We report a sensitive method for visual detection of mercury ions (II) (Hg²⁺) in aqueous solution by using gold nanoparticles (Au-NPs) and thymine (T)-rich hairpin DNA probes. The thiolated hairpin DNA probe was immobilized on the Au-NP surface through a self-assembling method. Another thymine-rich, digoxin-labeled DNA probe was introduced to form DNA duplexes on the Au-NP surface with thymine-Hg²⁺-thymine (T-Hg²⁺-T) coordination in the presence of Hg²⁺. The Au-NPs associated with the formed duplexes were captured on the test zone of a lateral flow strip biocomponent (LFSB) by immunoreaction events between the digoxin on the duplexes and anti-digoxin antibodies on the LFSB. The accumulation of Au-NPs produced a characteristic red band on the test zone, enabling visual detection of Hg²⁺ without instrumentation. A detection limit of 0.1 nM was obtained under optimal experimental conditions. This method provides a simple, rapid, sensitive approach for the detection of Hg²⁺ and shows great promise for point-of-care and in-field detection of environmentally toxic mercury.