Abstract
This work is a continuation of our research into the development of simple, reliable, and cost-effective methods for the early diagnosis of prostate cancer (PCa). The proposed method is based on the electrochemical detection of the PCA3 biomarker of PCa (long non-coded RNA transcript expressed in urine) using a specific aptamer labeled with a redox group (methylene blue). The electrochemical measurements (cyclic voltammograms) obtained from electrodes functionalized with the aptamer were complemented in this work by another biosensing technique: total internal reflection ellipsometry (TIRE). In addition to proving the concept of the detection of PCA3 in low concentrations down to 90 pM, this study improved our understanding of the processes by which PCA3 binds to its specific aptamer. The high specificity of the binding of PCA3 to the aptamer was assessed by studying the binding kinetics, which yielded an affinity constant (KD) of 2.58 × 10−9 M. Additional XPS measurements confirmed the strong covalent binding of aptamers to gold and showed spectral features associated with PCA3 to aptamer binding.
Highlights
Binding the target analyte (PCA3) to the aptamer caused the appearance of oxidation and reduction peaks at about −0.05 V and −0.06 to −0.08 V, respectively, which are associated with the oxidation and reduction potentials of methylene blue [27]
Evaluating the low detection limit was not the goal in this research study, since we aimed to prove the concept of detection; the minimum detected concentration of 1 nM is sufficient for prostate cancer (PCa) diagnosis based on the PCA3 biomarker
CG-3 RNA aptamer was carried out using several experimental methods: cyclic voltammograms, total internal reflection ellipsometry, and X-ray photoelectron spectroscopy
Summary
PCA3 was discovered a long time ago, until now, its use in prostate cancer diagnosis has been limited to the Progensa PCA assay, licensed in the USA in 2012. This assay detects PCa through PCR amplification of the mRNA of both PCA3 and PSA in the first-catch urine after a digital rectal examination and yields a PCA3 score (the ratio of PCA3 to PSA mRNA molecules in urine specimens) [5,6]. Studies regarding the clinical utility of the PCA3 urine assay for men in Europe and North America confirmed that a PCA3 score cut-off of 35 provides an optimal balance between sensitivity and specificity for PCa detection [6,7]. Demonstrated its potential in minimizing the number of unnecessary biopsies, as well as the cost of treatment [9]
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