Comparative performance of biopolymer-supported graphitic carbon nitride nanosheets for electrochemical carcinoembryonic antigen cancer biomarker detection in serum samples using smartphone device.

Carcinoembryonic antigen (CEA) is a critical biomarker expressed in several cancers, necessitating the development of an ultrasensitive and selective detection platform for early-stage cancer diagnosis and monitoring treatment responses. Therefore, a comparative study related to electrochemical immunosensor for CEA detection between utilization of biopolymer functionalized graphitic carbon nitride nanosheets (f-gC₃N₄ NS) and pristine graphitic carbon nitride nanosheets (gC₃N₄ NS) onto screen printed electrode (SPE) is presented. The synthesis of gC₃N₄ NS was achieved via exfoliation process, followed by the functionalization of prepared gC₃N₄ NS using chitosan and their depostion onto SPE surface. Further, prepared f-gC₃N₄ NS/SPE surface was immobilized with specific activated antibodies for CEA (anti-CEA) using N-ethyl-N'-(3-dimethyl aminopropyl) carbodiimide (EDC) and N-hydroxy succinimide (NHS) coupling chemistry, ensuring sturdy and stable antibody attachment. In addition, bovine serum albumin (BSA) protein was used as a blocking agent to minimize non-specific interactions. The stepwise modified SPE platform was confirmed through morphological, structural and electrochemical techniques. The fabricated f-gC₃N₄ NS based immunoelectrode i.e. BSA/anti-CEA/f-gC₃N₄ NS/SPE was tested with various CEA concentrations ranging from 0.0001 to 20 ng/mL using differential pulse voltammetry (DPV) technique, showcasing a sensitivity of 4.71 µA/log(ng/mL)/cm². However, a comparison study was performed with pristine gC₃N₄ NS i.e.BSA/anti-CEA/gC₃N₄ NS/SPE, showed change in current response with the function of CEA concentrations ranging from 0.0001 to 5 ng/mL, exhibiting a sensitivity of 1.42 µA/log(ng/mL)/cm². The highly improved electrochemical performance of the BSA/anti-CEA/f-gC₃N₄ NS/SPE immunosensor was achieved due to the availibility of abundant functional groups present in f-gC₃N₄ NS providing strong biomolecular interactions with anti-CEA as well as improved surface area. Further, the obtained electrochemical immunosensing results with standard CEA biomarker were compared and validated with colorimetric immunoassay kit. The findings highlights the performance of the fabricated BSA/anti-CEA/f-gC₃N₄ NS/SPE in terms of selectivity, specificity, reproducibility and accuracy along with its capability to be used for onsite diagnosis of CEA biomarker in serum samples using smartphone assisted portable electrochemical device.