Label-free, sensitive detection of Hg(II) with gold nanoparticles by using dynamic light scattering technique.

A label-free method for sensitive detection of Hg(2+) was developed with gold nanoparticles (AuNPs) by using dynamic light scattering (DLS) technique. Oligonucleotide 5'-TTT CTT CTT CGT TGT TGT TT-3' could transform from uncoil to rigid duplex or hairpin structure upon addition of Hg(2+) ions, which was confirmed by experiments of fluorescence resonance energy transfer and change of melting temperature. The change of DNA structure reduced its adsorption ability on the surface of AuNPs, and resulted in the aggregation of AuNPs in the salt solution, which could be estimated with average hydrodynamic diameter by using DLS technique. Under the optimum conditions, the average diameter increased linearly with the concentration of Hg(2+) over the range from 0.75 nM to 25 nM, the linear regression equation was D=46.7+2.0C (nM, R=0.9958), with a detection limit of 0.43 nM.