Ultrasensitive and visual detection of squamous cell carcinoma antigen based on a silver-enhanced sandwich immunoassay using AuNPs-C3N4 nanocomposites

Based on gold label silver stain (GLSS) method, a sandwich-type immunoassay for visual, ultrasensitive and specific detection of squamous cell carcinoma antigen (SCCA) was constructed using gold nanoparticlesraphite- like carbon nitride (AuNPs-C3N4). In this assay, the capture SCCA antibody (Ab1) was immobilized on the silanized slides via the Schiff's base links, and the AuNPs-C3N4 nanocomposite labeled by the detection SCCA antibody (Ab2) acted as the signal probe. The detection mechanism was as follows: Ab1 was immobilized onto the silanized slides in order to catch the target antigen SCCA, and then allowed the immobilization of the signal probe (Ab2) via the interaction between antigen and antibody. Compared with conventional GLSS method in which AuNPs are directly immobilized on Ab2, much more AuNPs corresponded to the antigen SCCA through AuNPs-C3N4 because g-C3N4 possessed larger surface area and loaded much more AuNPs than Ab2. Therefore, more AuNPs were exposed to silver ions during staining, more silver ions were reduced, and the sensitivity improved 1000-fold. The average grey values were linearly related to the logarithm of SCCA concentration from 0.001ng/mL to 100ng/mL, with high specificity, good reproducibility and long-term stability. Results suggested that the proposed sandwich immunoassay based on GLSS method is a simple, sensitive, selective, and visual tool for the detection of SCCA.