Iodide sensing via electrochemical etching of ultrathin gold films.

Iodide is an essential element for humans and animals and insufficient intake is still a major problem. Affordable and accurate methods are required to quantify iodide concentrations in biological and environmental fluids. A simple and low cost sensing device is presented which is based on iodide induced electrochemical etching of ultrathin gold films. The sensitivity of resistance measurements to film thickness changes is increased by using films with a thickness smaller than the electron mean free path. The underlying mechanism is demonstrated by simultaneous cyclic voltammetry experiments and resistance change measurements in a buffer solution. Iodide sensing is conducted in buffer solutions as well as in lake water with limits of detection in the range of 1 μM (127 μg L(-1)) and 2 μM (254 μg L(-1)), respectively. In addition, nanoholes embedded in the thin films are tested for suitability of optical iodide sensing based on localized surface plasmon resonance.