A New Type of Ca2+ Sensor Based on Direct Electrochemical Capacitance Method

First, 16-mercaptohexadecanoic acid was self-assembled onto the gold electrode surface via Au-S covalent bond. Calmodulin was then covalently immobilized onto the 16-mercaptohexadecanoic acid monolayer under the activation of EDC and NHS. Thus, a new type of capacitance Ca2+ sensor was constructed. The equivalent circuit analysis of the testing system was also performed. Using the home-made “Electrochemical Capacitance Analyzer”, concentration effect of the supporting electrolyte on the basis capacitance and the total capacitance change resulted from the combination of calmodulin with Ca2+ were studied. Its stability and the ability of the sensor to reproduce were also examined. The results showed that for the determination of Ca2+, the linear range extended from 10−8 M to 3 × 10−6 M and the detection limit was 1 × 10−9 M. The stability of the sensor would be retained for one month by immersing it in 0.02 M (pH 7.0) PBS at 4 °C. The sensor also could be reproduced by EDTA and the basis capacitance varied by not more than 0.3% after reproduction.