Detection of prostate cancer biomarker PCA3 with electrochemical apta-sensor

This is a continuation of our research into the development of novel biosensing technologies for early diagnostics of prostate cancer (PCa). The existing PCa diagnostics based on PSA detection (prostate cancer antigen) in blood serum often yield controversial outcomes and require improvement. At the same time, the long non-coded RNA transcript PCA3 overexpressed in PCa patients’ urine proved to be an ideal biomarker for PCa diagnosis, and recent research mainly focuses on developing biosensors for the detection of PCA3. One of the most promising directions in this research is the use of aptamers as bio-receptors for PCA3. We demonstrated the earlier great potential of electrochemical sensors exploiting aptamer labelled with redox group ferrocene. In this work, we use the RNA-based aptamer specific to 227 nt fragment of lncRNA PCA3 labelled with methylene blue redox label which offers a higher affinity to PCA3 than commonly used DNA-based aptamers. Before proceeding with biosensing experiments, the gold screen-printed electrodes were cleaned by CV scanning in a sulfuric acid solution, which removed surface contaminations and thus improved immobilization of aptamers. The quality of the gold surface was assessed by contact angle measurements. Moreover, the concentration of immobilized aptamers was optimized to achieve the best results in electrochemical measurements. Initial tests were carried out using cyclic voltammograms (CV) measurements and showed a correlation between oxidation/reductions peaks intensities and the concentration of PCA3. Such experiments proved the main concept of the proposed apta-sensing, e.g., the changes of aptamer secondary structure during binding the target (PCA3) resulting in redox labels coming closer to the electrode surface and thus increasing the charge transfer. The lowest recorded concentration of PCA3 was 0.01 nM in CV measurements, which is close to the LDL level for this method. Much more promising results were obtained with the electrochemical impedance spectroscopy (EIS) measurements, which showed remarkable features of increasing sensitivity at low concentrations of PCA3. The extrapolation of data below 0.05 nM level allowed estimating LDL of about 0.4 pM. The results obtained are very encouraging and constitute a major step towards developing a simple, reliable, and cost-effective diagnostic tool for the early detection of prostate cancer.