A novel immobilization strategy for electrochemical detection of cancer biomarkers: DNA-directed immobilization of aptamer sensors for sensitive detection of prostate specific antigen

We report on a novel strategy for DNA aptamer immobilization to develop sensitive electrochemical detection of protein biomarker, with prostate specific antigen (PSA) as a case biomarker. Thiolated single-stranded DNA was co-immobilized with 3-mercapto-1-propannol on gold electrodes, and used as a scaffold for DNA aptamer attachment through hybridization of the aptamer overhang (so-called “DNA-directed immobilization aptamer sensors”, DDIAS). In the approach, the complementary DNA aptamer against PSA was assembled by the probe ssDNA onto the electrode to detect PSA; or the probe ssDNA directly hybridized with complementary DNA aptamer/PSA complex following their pre-incubation in solution, so-called ‘on-chip’ and ‘in-solution’ method, respectively. A double stranded DNA intercalator with ferrocenyl (Fc) redox marker was synthesized to evaluate the feasibility of the strategy. Results demonstrate that ‘in-solution’ method offers a favourable media (in homogenous solution) for the binding between the aptamer and PSA, which shows to be more efficient than ‘on-chip’ approach. DDIAS show promising analytical performance under optimized conditions, with a limit of detection in the range of fM and low non-specific adsorption.