This disclosure describes new methods and devices for sensing redox-active analytes in solution. The invention combines a surface plasmon resonance (SPR) sensor and a chemical electrode sensor. A conducting layer which supports SPR is attached to a voltage source. The voltage source is also connected to a reference electrode, which is in the aqueous solution with the SPR sensor. As the voltage is varied, the analytes undergo oxidation and reduction at the surface of the conducting film. The current is measured, just as it would be in a standard chemical electrode, with current peaks appearing at different potentials indicating different ions in the solution. Unlike a standard chemical electrode, the surface of the conducting film is also used to excite a surface plasmon wave (SPW). The SPW provides new information which is not available from any standard chemical electrode, such as the effective index of refraction at the surface of the conducting film as the analytes are being oxidized and/or reduced. This additional source of information can be used to minimize the effects of overlapping stripping peaks and interspecies compound formation as well as determine the thickness of surface layers during measurements. Additionally, the simultaneous determination of reaction properties and optical properties of reaction products can provide additional information about the aqueous support solution such as the quantity and types of natural oxidants in solution, such as oxygen or hydroxides. The formation of oxides and hydroxides will lead to measurably different optical properties.