Graphitic carbon nitride/1-pyrenebutyric acid N-hydroxysuccinimide/polythiophene nanocomposite photoelectrochemical biosensor for CA 19-9 detection.

A photoelectrochemical (PEC) biosensor composed entirely of carbon nanomaterials was synthesized to detect carbohydrate antigen 19-9 (CA 19-9). The biosensor platform integrated graphitic carbon nitride (GCN), known for its light sensitivity, polythiophene (PTh), an organic conductive and optically active material, and 1-pyrenebutyric acid N-hydroxysuccinimide (PBASE), which functions both as a biolinker to conjugate CA 19-9 antibody and antigen and as an electron mediator to facilitate electron transfer from GCN to PTh. The formation of a Schottky heterojunction between PTh and GCN reduced the bandgap of GCN from 2.66 to 1.96 eV, which enhanced transfer of photogenerated electrons for cathodic photocurrent generation. The improvement of charge transfer due to heterojunction formation and π-π stacking between GCN and the pyrene group of PBASE is confirmed by cyclic voltammetry (CV), electron impedance spectroscopy (EIS), and chronoamperometry (CA) findings. The highest current of 1.31 μA is observed for combination of 5 wt% PTh with a GCN/PBASE ratio of 1:0.5. Besides evaluating the electron mobility of GCN/PBASE/PTh, CV, EIS, and CA were also used to evaluate the sensor performance. Optimization studies revealed that 0.6 μg of CA 19-9 antibody and 1 h of antigen-antibody immobilization time significantly improved the biosensor response. The GCN/PBASE/PTh biosensor demonstrated high sensitivity to CA 19-9 antigen across a concentration of 50-1000 U/ml and a detection limit as low as 0.052 U/ml. The reported working range is within the limits required for diagnostic testing of patients with hepatic and heart problems as well as for post-treatment monitoring of colorectal and pancreatic cancer patients.