Ratiometric Electrochemical Sensor for Selective Monitoring of Cadmium Ions Using Biomolecular Recognition

A selective, accurate, and sensitive method for monitoring of cadmium ions (Cd2+) based on a ratiometric electrochemical sensor was developed, by simultaneously modifying with protoporphyrin IX and 6-(ferroceney) hexanethiol (FcHT) on Au particle-deposited glassy carbon electrode. On the basis of high affinity of biomolecular recognition between protoporphyrin IX and Cd2+, the functionalized electrode showed high selectivity toward Cd2+ over other metal ions such as Cu2+, Fe3+, Ca2+, and so on. Electroactive FcHT played the role as the inner reference element to provide a built-in correction, thus improving the accuracy for determination of Cd2+ in the complicated environments. The sensitivity of the electrochemical sensor for Cd2+ was enhanced by similar to 3-fold through the signal amplification of electrodeposited gold nanoparticles. Accordingly, the present ratiometric method demonstrated high sensitivity, broad linear range from 100 mu M to 10 mu M, and low detection limit down to 10 mu M (2.2 ppb), lower than EPA and WHO guidelines. Finally, the ratiometric electrochemical sensor was successfully applied in the determination of Cd2+ in water samples, and the obtained results agreed well with those obtained by the conventional ICP-MS method.