Ultrasensitive detection of mercury (II) ions using electrochemical surface plasmon resonance with magnetohydrodynamic convection.

A high-precision technique that can detect mercury (II) ions down to 1 fM concentration in aqueous solutions is introduced. The technique combines the conventional electrochemical method, surface plasmon resonance (SPR), and magnetohydrodynamic (MHD) convection. Mercury ions are electroplated onto a gold SPR sensing surface, and then detected quantitatively by applying a potential scan with cyclic voltammetry. Both the SPR angular shift and the electrochemical current signal are recorded for identification and quantification of the mercury ions. The detection sensitivity is further enhanced by applying an MHD convection in the presence of a magnetic field, which does not require any moving parts intruding into the aqueous solution. The technique thus has a great advantage for small detection volume. In the presence of supporting electrolytes, 1 mM nitric acid and 10 mM potassium nitrate, Hg(2+) ionic solutions with concentrations ranging from 1 fM to 1 microM are tested under different magnetic flux densities of B=0, 0.27, 0.53, and 0.71 T. The experimental results demonstrate that the stripping signals of the 1 fM to 1 microM Hg(2+) ions are enhanced by 10-60% with the flux density B=0.71 T.