An ultrasensitive fluorescence immunosensor for SCCA detection based on Ag NPs@N-doped carbon quantum dots

An ultrasensitive fluorescence immunosensor based on silver nanoparticles@ nitrogen-doped carbon quantum dots (Ag NPs@N/CQDs) and exploiting the quenching effect of gold nanoparticles (Au NPs) was fabricated for squamous cell carcinoma antigen (SCCA) detection. Ag NPs@N/CQDs were immobilized on the surface of an indium tin oxide (ITO) electrode and then coupled with the primary antibody of SCCA. The primary antibody captured SCCA on the ITO electrode, forming an immune complex with the secondary antibody labeled with gold nanoparticles, thereby constructing a sandwich-structured fluorescent sensor. Using the prepared sensor, a new method for detecting trace amounts of SCCA in human serum was established. Owing to the effective quenching of fluorescence intensity of Ag NPs@N/CQDs by Au NPs, combined with the presence of a sandwich immune structure, the sensor exhibits high sensitivity and selectivity. The method demonstrates a linear range of 2 − 4000 fg mL −1 and a detection limit of 0.87 fg mL −1 . The the recovery rate for real serum samples was between 94.45 % to 103.43 %.