Overoxidized polypyrrole-osmium telluride quantum dots immunosensor for prostate specific antigen – A cancer biomarker.
Prostate cancer is a deadly disease that occurs in the male’s prostate gland. A prostate gland is a walnut structure that forms part of the male’s reproductive system. Prostate cancer is caused by high level than normal of PSA (Gleason score > 4 ng ml-1) in human blood. Some symptoms associated with high levels of PSA include blood in urine, pain when urinating, difficulty in getting and keeping an erection, blood in semen and pain in upper thigh. An immunosensor is a type of biosensor that has an antigen or antibody fragment as its biological recognition component. The specificity of the molecular recognition of antigen by antibodies to form a stable complex is the basis of immunosensor technology. In this work, overoxidized polypyrrole (OvoxPpy) was electrosynthesized as a novel sensor platform on glassy carbon electrode (GCE). The OvoxPpy was then doped with osmium telluride quantum dots(OsTe2QDs) by drop-coating method to form OsTe2QDs|OvoxPpy|GCE system. The morphology and the size of OsTe2QDs|OvoxPpy|GCE nanocomposite were determined using scanning electron microscopy. The size of thioglycolic acid capped osmium telluride quantum dots (TGA-OsTe2QDs) used as support material for the biosensor was about 2.289 nm. These quantum dots showed an excellent photo-absorption properties with an ultraviolet- visible (UV-Vis) photo absortion band occurring at 406nm associated with high band energy of 3.05 eV. The electrochemical immunosensor for PSA was prepared by immobilizing anti- PSA-antibody onto the OsTe2QDs|OvoxPpy|GCE by drop-coating and allowing it to dry for 2h. The nanocomposite sensor platform and the immunosensor were electrochemically characterised by voltammetric and impedimetric techniques. The phase shift in Bode diagram at maximum frequency was indicative of kinetic changes. Charge transfer resistance, Rct, was used as the analytical parameter for measuring the interfacial kinetics which occurred as a result of the bio-recognition event between anti-PSA-antibody and PSA. The impedance of the quantum dot electrode (TGA-OsTe2QDs-Nafion|GCE) was lower (1.490 x 104 kΩ) than the impedance of the immunosensor platform (BSA-Anti-PSA-antibody|TGA-OsTe2 QDs|OvoxPpy|GCE), 2.754 x 104. The Rct of the immunosensor was found to increase with increasing concentration of PSA. The linearity of the immunosensor at the very low concentration range (1.266 - 4.207 fg ml-1) tested, confirms its high sensitivity for PSA.