Quantification of BSA concentration by using Ag electrochemistry in chloride solution: extension of the linear range

An electrochemical approach to determine protein concentration, based on affinity of silver ion to protein was examined. A solid silver electrode was oxidized and reduced in PBS solution containing bovine serum albumin, BSA. Electrochemically generated silver ions produce AgCl or a complex with BSA. Reduction of AgCl and Ag-protein complex proceed at different potential which enables determination of the amount of Ag-protein complex. The ratio of the amounts of charge of these two processes serves as a basis for the determination of protein concentration. In this work it is demonstrated that the presence of sodium dodecyl sulfate (SDS) in protein solution improves the linear range of protein analysis. Lower detection limits of the method were practically estimated to be 0.04 and 0.08 mg·mL−1 BSA in the absence and in the presence of 2.5 mg·mL−1 SDS, respectively. The linear range was 0.04-0.12 mg·mL−1 (sensitivity 5 mL·mg−1) in absence and 0.08-0.3 mg·mL−1 (sensitivity 0.85 mL·mg−1) in the presence of SDS, respectively. A mathematical fitting procedure is described to calculate the charge needed to reduce AgCl and Ag-protein complex.