A facile indole probe for ultrasensitive immunosensor fabrication toward C-reactive protein sensing

C-reactive protein (CRP) is a protein biomarker for acute phase response. Herein, we fabricate a highly sensitive electrochemical immunosensor for CRP on a screen-printed carbon electrode (SPCE) with indole as a novel electrochemical probe and Au nanoparticles for signal amplification. Amongst, indole appeared as transparent nanofilms on the electrode surface, and underwent a one-electron and one-proton transfer to form oxindole during the oxidation process. Upon optimization of experimental conditions, a logarithmic correlation between CRP concentration (0.0001–100 μg∙mL−1) and response current was revealed with a detection limit of 0.03 ng∙mL−1 and a sensitivity of 5.7055 μA∙μg−1∙mL∙cm−2. The sensor exhibited exceptionally distinction selectivity, reproducibility and stability of the electrochemical immunosensor studied. The recovery rate of CRP in human serum samples determined by the standard addition method, ranged between 98.2–102.2%. Overall, the developed immunosensor is promising, and has the potential for CRP detection in real human serum samples.