A Fluorescence Signal "Turn-On" Lateral Flow Assay for Ultrasensitive Small-Molecule Detection

Fluorescence signal “turn-on” lateral flow immunoassays (FONLFAs) have the potential for improving the detection sensitivity compared with conventional lateral flow immunoassays (LFAs) due to lower-intensity background signals. FONLFAs involve the co-immobilization of fluorescent materials and antigens on a nitrocellulose (NC) membranes and the selection of an appropriate combination of nanoprobes and fluorescent nanomaterials. However, commonly, the co-immobilization of fluorescent materials and antigens is achieved via tedious chemical modifications. In addition, only few nanoprobes have been used as quenchers in FONLFAs so far.

Chifang Peng, Jiangnan University, Wuxi, China, and colleagues have developed a new strategy for the co-immobilization of fluorescent nanomaterials and antigens on nitrocellulose membranes to create FONLFAs. The team synthesized bright fluorescent gold nanoclusters with protamine (Prot-AuNCs) and obtained nanocluster/antigen aggregates via self-assembly. The aggregates can be then be easily immobilized on a nitrocellulose membrane by spraying them onto the material. The immobilization efficiency of aggregates reached 96 %, leading to assays with good stability and reproducibility.

The team used this platform with the pesticide carbendazim as a model target, Prot-AuNCs as a fluorescent donor, and one of four metal nanoprobes typically used in LFAs as a quencher. They found that all four nanoprobes showed improved naked-eye detection sensitivity and limits of detection in quantitative analysis compared with conventional colorimetric assays. Using Fe-polydopamine nanoparticles (FePNs), in particular, led to a 40- to 800-fold higher sensitivity than other representative colorimetric and fluorescence methods, and the naked-eye detection sensitivity of FePNs-FONLFAs can be improved 200-fold compared with conventional colorimetric AuNP-LFAs. These results highlight the potential of fluorescent nanocluster/antigen aggregates in fluorescence signal “turn-on” lateral flow immunoassays for small molecules.