Direct Measurement of Aqueous Mercury(II): Combining DNA-Based Sensing with Diffusive Gradients in Thin Films.

A highly specific DNA-functionalized hydrogel sensing layer was integrated with the diffusive gradients in thin films (DGT) technique for the direct determination of aqueous mercury(II). The DNA-functionalized layer in the DGT unit exhibited both high affinity (complexation constant = 10 at 25 °C) and high binding capacity (9.5 mg Hg disk) toward Hg. The diffusion coefficient for Hg complexed with common inorganic ligands was an order of magnitude higher than that for Hg complexed with natural dissolved organic matter: 9.0 × 10 versus 9.8 × 10 cm s at 25 °C. The performance of the DNA-DGT sensor was further assessed under variable pH (3-10) and temperature (5-40 °C) conditions, as well as across a range of hydrochemically diverse artificial and natural freshwaters. The observed effects of the environmental and solution compositional variables on Hg binding to the DNA in the sensing layer were successfully accounted for by equilibrium speciation calculations and temperature-corrected, multicomponent diffusion coefficients for aqueous Hg(II). The results therefore support the use of the DNA-DGT sensor as an alternative to traditional sampling and analysis methods for measuring aqueous Hg(II) concentrations down to the nanomolar level in freshwater environments.