Gold Nanoparticles with Ligand/Zwitterion Hybrid Layer for Individual Counting of Influenza A H1N1 Subtype Using Resistive Pulse Sensing.

Resistive pulse sensing (RPS) is an analytical technique for detecting particles with nano- to micrometer diameters, such as proteins, viruses, and bacteria. RPS is a promising tool for diagnosis as it can analyze the characteristics of target particles individually from ion current blockades as pulse waveforms. However, it is difficult to discriminate analog targets because RPS merely provides physical information such as size, shape, concentration, and charge density of the analyte. Influenza A virus, which is 80-120 nm in diameter, has various subtypes, demonstrating the diversity of virus characteristics. For example, highly pathogenic avian influenza infections in humans are recognized as an emerging infectious disease with high mortality rates compared with human influenza viruses. Distinguishing human from avian influenza using their differing biological characteristics would be challenging using RPS. To develop a highly selective diagnostic system for infectious diseases, we combined RPS with molecular recognition. Gold nanoparticles (GNPs) that have human influenza A (H1N1 subtype) virus-specific sialic acid receptors on the surface were prepared as a virus label for RPS analysis. A sulfobetaine and sialic acid (ligand) hybrid surface was formed on the GNPs for the suppression of nonspecific interaction. The results show a size change of viruses derived from specific interactions with GNPs. In contrast, no size shift was observed when nonspecific sialic acid receptor-immobilized GNPs were used. Detection of viruses by individual particle counting could be a new facet of diagnosis.