Development of prostate specific membrane antigen based immunosensor for early detection of the prostate cancer

Prostate Cancer (PK) is a type of cancer that usually develops in peripheral basal cells in men. In clinical diagnosis, serum Prostate Specific Antigen (PSA) test, digital rectal examination (DRE), and Trans-rectal Ultrasonography (TRUS) are commonly used. Needle biopsy is performed when either PRM, TRUS or PSA is over the limit of 4 ng /mL. As a result, Gleason Score is given to determine the stage of the disease based on the test results mentioned above. It is very important to make an early and accurate diagnosis of the disease, which causes high cancer mortality and morbidity in the second place after lung cancer in men. However, the fact that serum biomarker PSA being only a prostate specific biomarker not a prostate cancer specific one, that prevents accurate diagnosis of the disease. Therefore, it is important to develop high performance diagnostic methods/tools based on prostate cancer specific biomarkers that can be used in the accurate and early diagnosis of prostate cancer. Accordingly, the scope of this thesis is to develop mass sensitive quartz tunning fork (QTF) and screen-printed electrode (SPE) based electrochemical PSMA immunosensors targeting measurement of Prostate Specific Membrane Antigen (PSMA), which has been mentioned prostate cancer specific biomarker in the literature. In the first stage of the study, the QTF transducer surfaces have been modified with amino-rich amiloid-like protein nanofibers and plasma polymerized thin films, in turn. After surface activation, immobilization of PSMA antigen-specific antibody (a-PSMA) onto QTF surfaces was performed and the interaction of the developed immunosensor with the target analyte PSMA was monitored by measuring changes in resonance frequency. In the second step, the production of electrochemical immunosensor was aimed and to achieve this goal, SPE having gold working electrode was modified by cysteamine (Cys) functionalized gold nanoparticles (Cys-AuNp). After surface functionalization, 1'-Carbonyldiimidazole (CDI) was used for binding amino groups in Cys-AuNPs to carboxyl groups in a-PSMA that resulted in antibody immobilization and the interaction of the developed immunosensor with the target analyte -PSMA- was tested by voltammetric analysis and impedance spectroscopy, respectively. Cys-AuNp modification has improved the analytical signal performance of the immunosensor, allowing even picogram-level analyte detection both in physiological buffer solution (PBS, pH:7.4) also in serum. In summary, within the scope of the PhD thesis, the design of PSMA immunosensors, which may be used as supportive tool in prostate cancer diagnosis was achieved. The eligibility of produced biosensors for biodetection was investigated via measuring prostate cancer specific biomarker, PSMA, expressing protein/cells and the performance parameters of the developed immunosensors were evaluated. In conclusion, it is believed that, the presented electrochemical-based immunosensor in this PhD thesis will present an infrastructure for future diagnostic tools that are planned to be developed either for prostate cancer or other type of cancers.