Improving the performance of upconversion nanoprobe-based lateral flow immunoassays by supramolecular self-assembly core/shell strategies

Upconversion nanoparticles (UCNPs) have been used as probes in lateral flow immunoassays (LFIAs), because the probe provides an excellent signal-to-noise ratio by eliminating background-fluorescence from biological samples. However, the low photoluminescence efficiency, unfavorable hydrophilic modification and poor antibody conjugation are insurmountable challenges for the application of UCNPs to LFIAs. In this work, we have made a breakthrough by integrating friendly ligand-exchange and supramolecular self-assembly strategies. It is demonstrated that the Cucurbit[7]uril-based hydrophilic modification strategy can improve the photoluminescence of UCNPs by two-fold and significantly improves the stability of the UCNPs. More importantly, the supramolecular self-assembly strategy, which is 10 times more efficient than the carboxyl-amino reaction for antibody conjugation. The UCNPs were successfully applied to sandwich and competitive LFIAs for the sensitive detection of a pathogenic bacteria (Escherichia coli O157:H7) and micro-molecule (danofloxacin). In comparison with existing methods, we demonstrate that this novel method could enhance the sensitivity by 40 times, expand the detection range by one order of magnitude, and reduce the costs by 20 %–40%. This new method not only inherits the excellent matrix tolerance of UCNPs for the detection of bio-samples but also improves the performance of LFIAs with regards to their sensitivity, quantitative range, and cost.