Label-free impedimetric prostate cancer aptasensor with antifouling surface chemistry

Prostate cancer (PCa) is the second most common cause of cancer related mortality among Western men. Hence, it is becoming very crucial to be early diagnosed with a high sensitivity and accuracy to preclude worsening of PCa. We here report the development of a biosensor for the analysis of Prostate Specific Antigen (PSA), a biomarker for PCa present in blood, using a PSA-specific DNA aptamer on polycrystalline gold electrodes. The main emphasis is on a clinical application where a specific and sensitive label free detection could be performed in blood samples using Electrochemical Impedance Spectroscopy (EIS) to test for a panel of PCa biomarkers.

A PSA biosensor was constructed by immobilizing a mixed self-assembled monolayer comprising of (1) 11-mercaptoundecanoic acid for covalent immobilization of amine terminated DNA aptamers and (2) 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 (Rct) was observed when using ferro-/ferri-cyanide redox probes in solution. The incubation with the control protein Human Serum Albumin does not show any significant changes in Rct. Unlike in other reports, we observe a decrease in Rct primarily due to the partial screening of the DNA charge by the large PSA molecule. A discussion is presented on the effect of the measurement buffer on the values and the sign of Rct variations upon DNA aptamer-PSA binding and the need to carefully select suitable measurement conditions.

Therefore, this proposed DNA aptamer-based biosensor is a promising, cost effective, label free and sensitive electrochemical detection platform for the detection of PSA in clinical samples using a simple surface chemistry.