Label-Free Fluorescence Quantitative Detection Platform on Plasmonic Silica Photonic Crystal Microsphere Array

We have demonstrated the proof-of-concept of a label-free fluorescence quantitative detection platform based on gold nanoparticle (AuNP) enhancement intrinsic fluorescence of protein on the silica photonic crystal microsphere (SPCM) array. The label-free one-step competitive fluorescence immunoassay protocol has been proposed on the surface of the SPCM. Aflatoxin B1 (AFB1) as a model molecule was detected by the newly established method. AFB1-bovine serum albumin and monoclonal antibodies (Abs) of anti-AFB1 have been immobilized on the surfaces of SPCMs and AuNPs, respectively. AuNPs remarkably enhanced the intrinsic fluorescence of artificial antigens on the surface of the SPCM at near UV excitation. The simulation of electric field distribution showed that the maximum value of the near-field enhancement |E/E0| of the SPCM with AuNPs could reach 20. The label-free fluorescence enhancement effect comes from the synergistic effects of photonic crystal effect and AuNP plasmon effect. Such a label-free fluorescence detection method can provide a linear detection range from 0.1 to 10 ng/mL with a limit of detection of 0.025 ng/mL and good specificity for AFB1. The recovery rates in the spiked cereal samples were measured in the range of 84.07 ± 5.71%–101.02 ± 5.13%, which were consistent with that of the traditional enzyme linked immunosorbent assay method. The label-free detection platform displays great application potential in biology, medicine, agriculture, food industry, chemical industry, energy source, and environmental protection.