One-step immunoassay without washing steps for influenza A virus detection using ISFET.

A one-step immunoassay for influenza A virus detection was developed using two different microbeads and a filter-inserted bottle. Two bead types with diameters of 15 (capture bead) and 3 (detection bead) μm were prepared to specifically detect influenza A virus. Anti-influenza A virus antibodies were coated on both bead types, whereas urease was immobilized only on the detection bead. An influenza A-positive sample could form a sandwich complex with the capture and detection beads; this complex would not pass through the filter, which had a controlled pore size. As the detection bead was used at a limiting concentration, it would be prevented from crossing the filter; thus, it would further react with the substrate urea and consequently increase the pH. An influenza A-negative sample would fail to form the sandwich complex in the presence of the capture and detection beads. Accordingly, the detection bead would pass through the filter into the urea buffer and increase the pH. The pH change in the urease reaction could be quantitatively measured by an indicator such as phenol red or using ion-selective field-effect transistor (ISFET). This one-step immunoassay was used for the detection of influenza A virus in real samples. The receiver operating characteristic (ROC) plot analysis showed an area under the curve (AUC) value of 0.931; the sensitivity and specificity of the assay was 80% and 90%, respectively, at a cutoff value of 0.9986. These results demonstrate that the one-step immunoassay could increase the sensitivity of influenza A virus detection in real samples.