Target-Induced Displacement Reaction Accompanying Cargo Release from Magnetic Mesoporous Silica Nanocontainers for Fluorescence Immunoassay

A new fluorescence immunoassay strategy based on a target-induced displacement reaction with cargo release from protein-gated carbohydrate-functionalized magnetic mesoporous silica nanoparticles (MMSN) was developed for sensitive detection of small molecular mycotoxins (aflatoxin B-1, AFB(1) used in this case). To construct such an assay system, MMSN was initially functionalized with mannose-terminated silanes, then capped with biotinylated concanavalin A (Con A) entrapped rhodamine B (RB) within the pores through the carbohydrate-protein interaction, and then biotinylated monoclonal anti-AFB(1) capture antibody was conjugated to Con A-functionalized MMSN by the streptavidin-biotin chemistry. Gold nanoparticles (AuNP) heavily functionalized with invertase and bovine serum albumin-AFB(1) conjugate were utilized as the trace tag. With AFB(1) introduction, a competitive immunoreaction for the immobilized anti-AFB1 antibody on the MMSN was started between target analyte and the labeled AFB1 on the AuNP. Accompanied by AuNP, the carried invertase hydrolyzed sucrose in glucose and fructose. The generated glucose competed with the mannose for Con A and displaced the Con A-antibody complex from the MMSN, resulting in the opening of molecular gates owing to the uncapping of MMSN, thereby the entrapped RB could release from the pores. The released RB could be quantitatively determined by a fluorometer. Under optimal conditions, the fluorescence intensity decreased with the increasing AFB(1) concentration in the range from 0.01 to 5 ng mL(-1) with a detection limit (LOD) of 8 pg mL(-1) at the criterion. lntra- and interbatch assay precisions were lower than 9 and 9.5% (CV), respectively. The method featured unbiased identification of negative (blank) and positive samples. No significant differences at the 0.05 significance level were encountered in the analysis of naturally contaminated peanut samples between the fluorescence immunoassay and a commercialized enzyme-linked immunosorbent assay (ELISA) method.