WO3-Nanocrystal-Modified Electrodes for Ultra-Sensitive and Selective Detection of Cadmium (Cd2+) Ions

The detection of heavy metal ions is becoming increasingly important for environmental monitoring and personal safety protection. Owing to their large surface area and suitable conductivity, metal oxide semiconductor nanocrystals have been utilized in chemically modified electrodes for the rapid and low-cost detection of heavy metal ions. However, their sensitivity and selectivity for cadmium ion (Cd2+) detection still remains a challenge. Here, a method of ultra-sensitive and selective Cd2+ detection based on WO3-nanocrystal-modified electrodes is proposed and demonstrated. Colloidal WO3 nanocrystals were synthesized via a solvothermal route and then deposited onto a carbon electrode using a spin-coating method, forming the modification layer at room temperature. The WO3-nanocrystal-modified electrodes exhibit a remarkable signal transduction capability that converts Cd2+ adsorption into current output signals. The peak current was linear to the logarithm of the Cd2+ concentration from 1 nM to 10,000 nM when measured using the anodic stripping voltammetry method. The selectivity mechanism was studied and attributed to the high adsorption energy of cadmium on WO3 compared to other heavy metal ions. Employment of WO3 for a high-performance Cd2+-selective electrode opens many opportunities in portable ion-detection applications.