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The proof of concept of utilizing a microfluidic dielectrophoresis (DEP) chip was conducted to rapidly detect a dengue virus (DENV) in vitro based on the fluorescence immunosensing. The mechanism of detection was that the DEP force was employed to capture the modified beads (mouse anti-flavivirus monoclonal antibody-coated beads) in the microfluidic chip and the DENV modified with fluorescence label, as the detection target, can be then captured on the modified beads by immunoreaction. The fluorescent signal was then obtained through fluorescence microscopy, and then quantified by ImageJ freeware. The platform can accelerate an immuno-reaction time, in which the on-chip detection time was 5 min, and demonstrating an ability for DENV detection as low as 10 4 PFU/mL. Furthermore, the required volume of DENV samples dramatically reduced, from the commonly used ~50 µL to ~15 µL, and the chip was reusable (>50x). Overall, this platform provides a rapid detection (5 min) of the DENV with a low sample volume, compared to conventional methods. This proof of concept with regard to a microfluidic dielectrophoresis chip thus shows the potential of immunofluorescence based-assay applications to meet diagnostic needs. [ABSTRACT FROM AUTHOR]

The continuous mutation of SARS-CoV-2 highlights the need for rapid, cost-effective, and high-throughput detection methods. To better analyze the antibody levels against SARS-CoV-2 and its variants in vaccinated or infected subjects, we developed a multiplex detection named Barcode Bead Fluorescence (BBF) assay. These barcode beads were magnetic, characterized by 2-dimensional edges, highly multiplexed, and could be decrypted with visible light. We conjugated 12 magnetic barcode beads with corresponding nine spike proteins (wild-type, alpha, beta, gamma, delta, and current omicrons), two nucleocapsid proteins (wild-type and omicron), and one negative control. First, the conjugated beads underwent serial quality controls via fluorescence labeling, e.g., reproducibility (R square = 0.99) and detection limits (119 pg via anti-spike antibody). Next, we investigated serums from vaccinated subjects and COVID-19 patients for clinical applications. A significant reduction of antibody levels against all variant beads was observed in both vaccinated and COVID-19 studies. Subjects with two doses of mRNA-1273 exhibited the highest level of antibodies against all spike variants compared to two doses of AZD1222 and unvaccinated. We also found that COVID-19 patients showed higher antibody levels against spike beads from wild-type, alpha, beta, and delta. Finally, the nucleocapsid beads served as markers to distinguish infections from vaccinated subjects. Overall, this study developed the BBF assay for analyzing humoral immune responses, which has the advantages of robustness, automation, scalability, and cost-effectiveness. [ABSTRACT FROM AUTHOR]