Label-free impedimetric aptasensor with antifouling surface chemistry: A prostate specific antigen case study

We here report the development of an aptamer based biosensor for the investigation of prostate specific antigen (PSA), a biomarker found in blood for prostate cancer (PCa), using electrochemical impedance spectroscopy (EIS). The study concentrates on a clinical application where a specific and sensitive label-free detection could be performed in real blood samples using EIS. Two types of PSA aptasensor were fabricated by immobilizing (i) a self-assembled monolayer comprising of 6-mercaptohexanol (MCH) and thiolated-DNA aptamer and (ii) 11-mercaptoundecanoic acid for covalent immobilization of amine terminated DNA aptamers and sulfo-betaine terminated thiol as an antifouling agent on a polycrystalline gold surface. Upon incubation of PSA with the DNA aptamer-based biosensor a decrease of charge transfer resistance (R-ct) was observed due to the partial screening of the DNA aptamer charge by PSA. Thiol terminated sulfo-betaine based sensors can detect PSA levels lower than 1 ng/ml. Validation of the aptasensor is provided by surface plasmon resonance measurements. Sulfo-betaine moiety also prevents any significant non-specific binding of the control protein human serum albumin (HSA) as compared to high non-specific binding with MCH-based sensors. A debate is presented on the effect of the measurement buffer on the values and the direction of R-ct changes on the aptasensors and the need to cautiously select suitable measurement conditions in order to obtain reliable results. This is the first report to date where a DNA aptamer-based biosensor was developed using thiol-terminated sulfo-betaine, which is a simple surface chemistry for the development of promising, cost-effective, label-free and sensitive electrochemical detection platforms for a range of analytes. (C) 2014 Elsevier B.V. All rights reserved.