Combination of the NanoSuit method and gold/platinum particle-based lateral flow assay for quantitative and highly sensitive diagnosis using a desktop scanning electron microscope

Owing to its simplicity and low cost, the lateral flow assay (LFA) is one of the most commonly used point-of-care diagnostic techniques, despite its low sensitivity and poor quantification. Here, we report a newly developed LFA-NanoSuit method (LNSM) combined with a desktop scanning electron microscope (SEM) for the direct observation of immunocomplexes labeled with a colloidal metal instead of signal enhancement strategies, such as using color, electrochemical signals, silver enhancement, magnetic properties, luminescent, and surface-enhanced Raman spectroscopy (SERS). The proposed LNSM suppresses cellulose deformity, thereby allowing the acquisition of high-resolution images of gold/platinum-labeled immunocomplexed pathogens such as influenza A, without conductive treatment as in conventional SEM. Electron microscopy-based diagnosis of influenza A exhibited 94 % clinical sensitivity (29/31; 95 % confidence interval [CI]: 79.398.2 %) and 100 % clinical specificity (95 % CI: 98.1100 %), which was more sensitive (71.4 %) than visual detection (14.3 %), especially in the lower influenza A-RNA copy number group. The detection ability of our method was nearly comparable to that of real-time reverse transcription-PCR. This is the first report on the diagnosis of clinical diseases using LFA equipped with a desktop SEM. This simple and highly sensitive quantitative analysis method involving LFA can be used to diagnose various diseases in humans and livestock, including highly infectious diseases such as COVID-19. (C) 2021 The Authors. Published by Elsevier B.V.

Automated summary

The newly developed LFA-NanoSuit method (LNSM) combined with a desktop scanning electron microscope (SEM) allows for direct observation of immunocomplexes labeled with a colloidal metal, achieving high clinical sensitivity and specificity for diagnosing pathogens like influenza A. This method's detection ability is nearly comparable to real-time reverse transcription-PCR, offering a simple and highly sensitive quantitative analysis method for diagnosing various diseases in humans and livestock, including highly infectious diseases such as COVID-19.