An amplified surface plasmon resonance "turn-on" sensor for mercury ion using gold nanoparticles.

Inorganic mercury ion (Hg(2+)) has been shown to coordinate to DNA duplexes that feature thymine-thymine (T-T) base pair mismatches. This observation suggests that an Hg(2+)-induced conformational change in a single-stranded DNA molecule can be used to detect aqueous Hg(2+). Here, we have developed an analytical method using surface plasmon resonance (SPR) to develop a highly selective and sensitive detection technique for Hg(2+) that takes advantage of T-Hg(2+)-T coordination chemistry. The general concept used in this approach is that the "turn-on" reaction of a hairpin probe via coordination of Hg(2+) by the T-T base pair results in a substantial increase in the SPR response, followed by specific hybridization with a gold nanoparticle probe to amplify the sensor performance. Meanwhile, the limit of detection is 1 nM, which is lower than other recently developed techniques. A linear correlation is observed between the measured SPR reflectivity and the logarithm of the Hg(2+) concentration over the concentration range of 5-5000 nM. Additionally, the SPR system provides high selectivity for Hg(2+) in the presence of other divalent metal ions up to micromolar concentration levels. The proposed approach is also successfully utilized for the determination of Hg(2+) in water samples.