One-step porous gold fabricated electrode for electrochemical impedance spectroscopy immunosensor detection

Abstract

A porous gold electrode fabricated by a simple one-step electro-process was employed for the first time to enhance a label-free immunosensor detection based on electrochemical impedance spectroscopy (EIS). The porous gold surface was simply fabricated using an applied potential of 1.50V in 100s, providing a 19±1 times larger surface area than the flat gold electrode. The larger surface area enhanced the performance of an immunosensor by increasing the amount of the immobilized antibody. The antibody–antigen pair of anti-human serum albumin (anti-HSA) and human serum albumin (HSA) was use as a model for the direct immunosensor detection. Porous and flat gold electrodes were modified with anti-HSA via a self-assembled monolayer (SAM) of 11-mercaptoundecanoic acid (11-MUA) and thiourea and a polymer layer of polytyramine and their performance was tested by EIS technique. The effect of two blocking solutions bovine serum albumin (BSA) and 1-dodecanethiol were also tested. The porous electrode modified with anti-HSA via the SAM of 11-MUA and blocked with BSA provided the highest sensitivity and the lowest detection limit, of up to 8.7 times and two order of magnitude compared with the flat electrode, respectively. The electrode can be reused for up to 40 times. The system was used to analyze albumin in serum and urine samples and the results agreed well with the photometric bromocresal green method for serum sample and an immunoturbidimetric assay for urine sample (P>0.05). This method could be easily applied to other label-free affinity pairs.