The response dynamics of indium telluride quantum dots impedimetric genosensor for telomerase cancer biomarker
Douman, Samantha Fiona
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Cancer, the second most common cause of death after heart disease, is a complex and multifactorial disease that up to date is still under extensive research. To achieve early detection of cancer disease the discovery of specific, sensitive and reliable biomarkers is required. Telomerase is a ribonucleo-protein complex that has been identified as an important target for cancer diagnostics and cancer therapy, because 85% of more than 950 primary tumours express telomerase activity. The standard method for the detection and quantification of telomerase activity is the polymerase chain reaction (PCR)-based assay known as the telomeric repeat amplification protocol (TRAP) assay. TRAP and other methods developed for telomerase detection have limitations for example its time consuming, requires complicated machinery, expensive equipment and reagents thus there is a need for a more sensitive, reliable and high-throughput method. Electrochemical biosensors are quickly emerging as an alternative for early detection of cancer because they can be designed to detect developing cancer biomarkers and to allow improved monitoring of cancer growth and patient therapy. This research study reported for the first time the successful fabrication and implementation of highly sensitive 3-mercaptopropionic acid indium telluride quantum dots (3MPA-In2Te3 QDs) based genosensor for detection of telomerase biomarker. The colloidal poly-dispersed 3MPA-In2Te3 QDs introduced into the genosensor system were successfully synthesized by a simple, inexpensive and reproducible aqueous method. The as prepared 3MPA-In2Te3 QDs was characterized by Ultraviolet Visible (UV-VIS) spectroscopy, Fluorescence (FL) spectroscopy, X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR) spectroscopy and High Resolution Transmission/Scanning Electron Microscopy (HR TEM/SEM). Electro-analysis of 3MPA-In2Te3 QDs was done by Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS). HR-TEM studies revealed formation of small sized QDs about 6 nm in diameter while UV-VIS studies showed presence of iv absorption peaks in the ultraviolet region (100-400 nm) which confirmed the formation of these small sized QDs. The good electrochemical, optical, physical and chemical properties of the 3MPA-In2Te3 QDs allowed them to be used as a mediating platform between deoxyribonucleic acid (DNA) and gold electrode (AuE). The successful detection of telomerase was achieved by hybridization process between the probe single stranded deoxyribonucleic acid (ssDNA) drop coated on the 3MPA-In2Te3 QDs/AuE surface and its complementary ssDNA in biological buffer solution (0.10 M tris-ethylenediamine tetraacetic acid (TE) buffer solution, pH 8.00). The response of the 3MPA-In2Te3 QDs based genosensor towards different concentration of complementary ssDNA was studied by CV, square wave voltammetry (SWV) and EIS. It was observed that all three analytical techniques exhibited good linearity since their linear correlation coefficients (R2) corresponded to 0.99. However, it was observed that EIS was the best technique for the detection of telomerase compared to both CV and SWV since it showed a higher sensitivity (2.44 Ω/nM) towards detecting telomerase with a detection limit as low as 0.00014 ng/mL. Control experiments were also carried out by monitoring the hybridization process in the presence and absence of complementary ssDNA and it was determined that the QDs based genosensor was highly selective towards complementary ssDNA. In view of the attractive analytical characteristics and advantages, the ultimate goal of the developed QDs based genosensor is to apply it in real clinical samples of cancer cells or bodily fluids of cancer patients for the detection of telomerase cancer biomarker.