Naked-eye counting of pathogenic viruses by phage-gold nanobiomaterials as probes

Early and sensitive detection of avian influenza virus (AIV) such as H9N2 is needed as AIV threatens human health and the food industry. Here, we developed an ultrasensitive and naked-eye counting strategy for quantifying AIV by two probes. One probe was a complex of M13 phage and gold nano particles (GNPs) modified with antiphage and anti-AIV antibody. The other probe was magnetic nano particles modified with the same anti-AIV antibody. The two probes cocaptured target AIV to form a sandwich structure. Because each M13-GNP probe contains multiple phages and each phage could be plated into an eye-visible plaque, the phages acted as a signal amplifier. After the phages from the sandwich structure were plated, the copy numbers of resultant plaques and target AIV were numerically correlated. Consequently, counting the number of the plaques with the naked eyes resulted in the quantification of the target AIV. The sensitivity of the naked-eye counting strategy for quantification of AIV was determined to be down to 50 PFU/mL, close to the sensitivity of digital polymerase chain reaction. With the feature of ultrasensitivity, the phage-GNP probeemediated naked-eye counting method holds a great promise for early visualized quantification of pathogenic viruses such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). (c) 2020 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Automated summary

An ultrasensitive naked-eye counting strategy was developed for quantifying AIV using phage-GNP probes, with a sensitivity down to 50 PFU/mL and potential application for pathogenic viruses like SARS-CoV-2.