An amplified surface plasmon resonance “turn-on” sensor for mercury ion using gold nanoparticles

► We develop a “turn-on” SPR sensor for Hg 2+ by using DNA hairpin probes. ► Our approach provides increasing sensitivity with gold nanoparticle amplification. ► This assay can provide practical applications toward Hg 2+ monitoring. 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.