Electrochemical-Signal-Amplification Strategy for an Electrochemiluminescence Immunoassay with g-C3N4 as Tags

Signal amplification for electrochemiluminescence (ECL) has conventionally been achieved by employing effective matrixes that can accelerate the electrochemical redox processes or carry more electrochemiluminophores. Herein, a convenient signal-amplification strategy was proposed for an ECL immunoassay with carboxylated g-C 3 N 4 nanosheets (NSs) as tags and carcinoembryonic antigen (CEA) as the model target via electrochemically pretreating the substrate: a glassy-carbon electrode (GCE) modified with a polymerized 2-aminoterephthalic acid (ATA) film (GCE/ATA). Bioconjugates of g-C 3 N 4 NSs and the signal CEA antibody (Ab 2 ) (i.e., g-C 3 N 4 NS–Ab 2 ) were immobilized on GCE/ATA via a sandwich immunoreaction to form GCE/ATA–Ab 1 –Ag–Ab 2 –NSs. Electrochemical-impedance spectroscopy and potential-resolved ECL characterization proved that GCE/ATA plays an important role in the electron-transfer resistance ( R et ) of the GCE/ATA–Ab 1 –Ag–Ab 2 –NSs for ECL and that successively scanning GCE/ATA–Ab 1 –Ag–Ab 2 –NSs from 0 to −1.6 V in K 2 S 2 O 8 - and H 2 O 2 -containing medium could reduce the R et and bring out 3.3-times-enhanced ECL at the 10th scan cycle compared with that of the 1st scan cycle, which was about 10.2 times the ECL of the GCE/ATA–Ab 1 –Ag–Ab 2 –NSs in medium containing merely K 2 S 2 O 8 . Inspired by this, direct and successive scanning of GCE/ATA in K 2 S 2 O 8 - and H 2 O 2 -containing medium was employed during fabrication, which dramatically reduced the R et of GCE/ATA–Ab 1 –Ag–Ab 2 –NSs and brought out obviously enhanced ECL responses for selectively determining CEA from 0.1 pg/mL to 1 ng/mL, with a detection limit of 3 fg/mL.