▎ 摘　　要

NOVELTY - Preparing a composite electrode comprises mixing an equal volume of graphene quantum dots and gold nanorods; sonicating the obtained mixture to obtain solution of the composite electrode; and modifying the obtained composite electrode using chitosan and drying the modified electrode at room temperature. USE - The methods are used for preparing a composite electrode; and making a biosensing platform (all claimed). ADVANTAGE - Provided is a sensor with simultaneous sensing based on two sensing platforms i.e. PSA aptasensor and PSA immunosensor and using two different techniques i.e. voltammetry (differential pulse voltammetry (DPV)) and impedance spectroscopy, which make sensing reliable, specific, sensitive and cost effective. DETAILED DESCRIPTION - Preparing a composite electrode comprises (a) mixing an equal volume of graphene quantum dots and gold nanorods; (b) sonicating the mixture obtained in step (a) for greater than or equal to 30 minutes to obtain solution of the composite electrode; (c) modifying the composite electrode obtained in step (b) using chitosan and drying the modified electrode at room temperature; and (d) washing the electrode with phosphate buffered saline (PBS) buffer at pH=7.4, where the composite electrode thus obtained has substantially high electron transfer ability; and the composite electrode has increased surface area and active sites for electron transfer of composite materials. INDEPENDENT CLAIMS are included for: (1) making a biosensing platform by (a) immobilizing an anti-Prostate Specific Antigen (PSA) on a composite electrode, (b) incubating the electrode obtained in step (a) overnight in a humid chamber; (c) washing the incubated electrode of step (b) with buffer to remove any loosely bounded anti-PSA; (d) immobilizing the electrode with bovine albumin serum (BSA) to block non-specific sites; (e) incubating immobilized electrode of step (d) for 2 hours and drying the same; and (f) washing the dried bio-electrode with buffer to obtain the biosensing platform on the electrode; where, the composite electrode is a modified chitosan-graphene quantum dots gold nanorods (CH-GQDs-AuNRs) composite; the biosensor has a regression coefficient of 0.980 for an aptasensor at PSA concentration of 0.14-11.6 ng/mL with a detection limit of 0.14 ng/mL; and the biosensor has a regression coefficient of 0.990 for an immunosensor at PSA concentration of 0.14-11.6 ng/mL with a detection limit of 0.14 ng/mL; and (2) a biosensing platform comprising: a base consisting of a composite electrode having a surface, the composite electrode comprising CH-GQDs-AuNRs composite; a layer of chitosan on the surface of the base; and a bio-active molecule immobilized on the layer of chitosan; where: the chitosan layer prevents stacking of graphene quantum dots; the chitosan enhances biosensitivity of the platform; and the biosensing platform shows variation in electron transferability, the variation being indicative of an interaction of the immobilized bioactive molecule in certain conditions.