Fig. 5: Overview of the capacitive biosensor system for airborne H5N1 detection.

a Aerosols containing pathogens released from infected animals are captured using a wet cyclone particle sampler. The collected sample is then processed by the capacitive biosensing unit. b Fabrication of the Prussian blue/graphene oxide (PB/GO)-based sensor, where PB and GO are co-deposited to form a redox-active capacitive layer (Cr) on a screen-printed carbon electrode (SPCE). Capture probes—aptamers or antibodies—are immobilized via glutaraldehyde cross-linking. At the biosensor–sample interface, double-layer capacitance (Cdl) forms, while diffusion capacitance (Cdf) arises from the ion diffusion layer. Binding of target pathogens to the capture probes changes the total capacitance (Ctot), enabling detection. c Capacitive biosensor responses for varying concentrations of H5N1. d Sensitivity assessment of the H5N1 biosensor using serial dilutions in PBS, showing a strong linear correlation (R² ≥ 0.95) between normalized ΔC% and log concentration, with significant differences between concentrations (t-test, p < 0.01). e Decision workflow for quasi-quantification of airborne H5N1, where samples are sequentially tested without dilution, 10× dilution, and 100× dilution to classify concentrations relative to the limit of detection (LoD). f Quasi-quantification of H5N1 aerosols collected via the wet cyclone sampler, with results classified as positive (Ο) or negative (X) based on normalized ΔC% relative to the H5N1 limit of detection (LoD)²⁸. This publication is licensed under CC BY-NC-ND 4.0 (https://creativecommons.org/licenses/by-nc-nd/4.0/).