Ultrasensitive lateral flow immunoassay for staphylococcal enterotoxin B using nanosized fluorescent metal–organic frameworks

Owing to their outstanding optical properties and superior physical/chemical stability, dye-doped fluorescent nanoparticles (NPs) are growing exponentially as signal labels of immunochromatographic lateral flow immunoassay (LFA) for the detection of various analytes. However, the key challenge in the design of these fluorescent NPs is to confine the fluorophores inside NPs at extreme concentrations, at which dyes tend to self-quench resulting from the formation of non-fluorescent aggregates. Looking for other advantageous nanomaterials, we propose for the first time the use of a nanosized fluorescent metal-organic framework (nanoMOF) in LFA for the detection of staphylococcal enterotoxin B (SEB) as a model analyte. Featured by the chromophore assembly, the nanoMOF exhibited a high dye loading (∼60%) and strong fluorescence intensity, which was due to the reduced self-quenching of dyes in a variety of MOF matrices. The strong green fluorescence intensity of the nanoMOF gives a high contrast against the background of the strips and the sensitivity reflected by photoluminescence was improved by the enhanced antenna effect. Furthermore, due to the high surface area for antibody stemming, the limit of detection (LOD) of the MOF based LFA for SEB detection was as low as 0.025 ng mL-1. The compatibility of the MOF based LFA with dairy samples and its stability under long-term storage conditions were also demonstrated. The integration of a nanoMOF into LFA to detect toxins could inspire the utilization of such nanomaterial-based labels in similar immunochromatographic testing methods to improve their performance.