Plasmonic Approach to Fluorescence Enhancement of Mesoporous Silica-Coated Gold Nanorods for Highly Sensitive Influenza A Virus Detection Using Lateral Flow Immunosensor

Rapid diagnostic tests based on the lateral flow immunoassay(LFI)enable early identification of viral infection, owing to simple interpretation,short turnaround time, and timely isolation of patients to minimizeviral transmission among communities. However, the LFI system requiresimprovement in the detection sensitivity to match the accuracy ofnucleic acid amplification tests. Fluorescence-based LFIs are moresensitive and specific than absorption-based LFIs, but their performanceis significantly affected by fundamental issues related to the quantumyield and photobleaching of fluorophores. Metal-enhanced fluorescence(MEF), which is a plasmonic effect in the vicinity of metallic nanoparticles,can be an effective strategy to improve the detection sensitivityof fluorescence-based LFIs. The key factors for obtaining a strongplasmonic effect include the distance and spectral overlap of themetal and fluorophore in the MEF system. In this study, MEF probeswere designed based on core-shell nanostructures employinga gold nanorod core, mesoporous silica shell, and cyanine 5 fluorophore.To optimize the efficiency of MEF probes incorporated on the LFI platform(MEF-LFI), we experimentally and theoretically investigated the distancedependence of plasmonic coupling between cyanine 5 and gold nanorodsby adjusting the shell thickness, resulting in significant fluorescenceenhancement. The proposed MEF-LFI enabled highly sensitive detectionof influenza A virus (IAV) nucleocapsid protein with a detection limitof 0.52 pg mL(-1) within 20 min and showed high specificityand accuracy for determining IAV clinical samples. Overall, our findingsdemonstrate the potential of this method as an effective tool formolecular diagnosis under emergency conditions.

Automated summary

Rapid diagnostic tests based on lateral flow immunoassay (LFI) can identify viral infections early, with simple interpretation, short turnaround time, and timely isolation of patients to minimize viral transmission. However, improvements are needed in the detection sensitivity of the LFI system to match nucleic acid amplification tests.