FM-aM Detection of the SARS-CoV-2 Antigen by Advanced Lateral Flow Immunoassay Based on Gold Nanospheres

Yilin Liu, Li Zhan, Jesse W. Shen, Bàrbara Baro, Andrea Alemany, James Sackrison, Oriol Mitjà, John C. Bischof

Research output: Contribution to journalArticlepeer-review

23 Scopus citations


The SARS-CoV-2 global pandemic created an unprecedented need for rapid, sensitive, and inexpensive point-of-care (POC) diagnostic tests to treat and control the disease. Many POC SARS-CoV-2 lateral flow immunoassays (LFAs) have been developed and/or commercialized, but with only limited sensitivity (μM-fM). We created an advanced LFA based on gold nanospheres (GNSs) with comprehensive assay redesign for enhanced specific binding and thermal contrast amplification (TCA) on GNSs for signal amplification, which enabled fM-aM detection sensitivity for SARS-CoV-2 spike receptor-binding domain (RBD) proteins within 30 min. The advanced LFA can visually detect RBD proteins down to 3.6 and 28.6 aM in buffer and human nasopharyngeal wash, respectively. This is the first reported LFA achieving sensitivity comparable to that of the PCR (aM-zM) by visual reading, which was much more sensitive than traditional LFAs. We also developed a fast (<1 min) TCA reading algorithm, with results showing that this TCA could distinguish 26-32% visual false negatives for clinical commercial LFAs. When our advanced LFAs were applied with this TCA, the sensitivities were further improved by eightfold to 0.45 aM (in buffer) and 3.6 aM (in the human nasopharyngeal wash) with a semiquantitative readout. Our proposed advanced LFA with a TCA diagnostic platform can help control the current SARS-CoV-2 pandemic. Furthermore, the simplicity and speed with which this assay was assembled may also facilitate preparedness for future pandemics.

Original languageEnglish (US)
Pages (from-to)13826-13837
Number of pages12
JournalACS Applied Nano Materials
Issue number12
StatePublished - Dec 24 2021

Bibliographical note

Funding Information:
This work was supported by the National Science Foundation (CBET- 2029474). J.C.B. acknowledges the Kuhrmeyer Chair in Mechanical Engineering and the Medtronic-Bakken Endowed Chair for Engineering in Medicine. The authors gratefully acknowledge a seed grant from the University of Minnesota (UMN) Medical school to develop SARS-CoV-2 diagnostics. B.B. is a Beatriu de Pinós postdoctoral fellow granted by the Government of Catalonia’s Secretariat for Universities and Research and by the Marie Sklodowska-Curie Actions COFUND Programme (BP3, 801370). This work was also supported by internal funds from Fundació Institut d’Investigació en Ciències de la Salut Germans Trias i Pujol and crowdfunding campaign. The fluorescence tests were performed at the Biophysical Technology Center, Department of Biochemistry, Molecular Biology, and Biophysics at UMN. TEM imaging was carried out in the Characterization Facility, UMN. The authors thank Dr. Guebum Han and Dr. Michael McAlpine for helping print gold nanoparticle solutions onto the membrane in preparing calibration strips, Dr. Zhe Gao for acquiring TEM images and helpful discussion on chemical reactions, Dr. Wei Shen for giving Y.L. and J.W.S access to the spectrophotometer, Dr. David Boulware for the helpful discussion on clinical samples and tests, Jacqueline Pasek-Allen for the helpful discussion on the PEGylation reaction, and Laura Bischof and Susan Everson for their help with writing improvement.

Publisher Copyright:
© 2021 The Authors. Published by American Chemical Society.


  • SARS-CoV-2
  • assay optimization
  • lateral flow immunoassay
  • sensitivity
  • thermal contrast amplification


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