Spectroscopic Ellipsometry Detection of Prostate Cancer Bio-Marker PCA3 Using Specific Non-Labeled Aptamer: Comparison with Electrochemical Detection ^†

The most common prostate cancer (PCa) diagnostics, which are based on detection of prostate-specific antigens (PSA) in blood, have specificity limitations often resulting in both false-positive and false-negative results; therefore, improvement in PCa diagnostics using more specific PCa biomarkers is of high importance. Studies have shown that the long noncoding RNA Prostate Cancer Antigen 3 (lncPCA3) that is over-expressed in the urine of prostate cancer patients is an ideal biomarker for non-invasive early diagnostics of PCa. Geno-sensors based on aptamer bioreceptors (aptasensors) offer cost- and time-effective, and precise diagnostic tools for detecting PCa biomarkers. In this study, we report on further developments of RNA-based aptasensors exploiting optical (spectroscopic ellipsometry) measurements in comparison with electrochemical (CV and IS) measurements published earlier. These sensors were made by immobilization of thiolated CG-3 RNA aptamers on the surface of gold. Instead of a redox-labelled aptamer used previously in electrochemical measurements, a non-labelled aptamer was used here in a combination with total internal reflection ellipsometry (TIRE) measurements. The results obtained by these two methods were compared. The method of TIRE is potentially highly sensitive and comparable in that respect with electrochemical methods capable of detection of PCA3 in sub-pM levels of concentration. The required selectivity is provided by the high affinity of PCA3-to-aptamer binding with K_D in the 10⁻⁹ M range. The spectroscopic ellipsometry measurements provided additional information on the processes of PCA3 to aptamer binding.