Aptamer-functionalized impaction electrode for label-free impedimetric detection of airborne bacteria

Rapid bioaerosol monitoring is constrained by the physical separation between aerosol collection and analytical readout, which introduces sample loss, dilution, and handling delays. Here, we move the bioreceptor to the front of this analytical chain. A thiolated DNA aptamer against Moraxella osloensis was immobilized on a screen-printed gold electrode (SPGE), and bioaerosol was impacted directly onto that receptor layer through a confined microliter buffer well, so recognition occurs where capture occurs and is read by label-free electrochemical impedance spectroscopy (EIS) without an intermediate transfer step. Integrating the receptor at the impaction interface left the voltammetric and impedimetric readouts unchanged, yielding a linear calibration range from 1.4 to 1.4 × 10⁴ CFU/μL (R² = 0.997, detection and quantification limits 0.87 and 54.5 CFU/μL). Because the folded aptamer requires a hydrated interface, sampling was bounded by buffer evaporation rather than capture efficiency, a physical constraint absent in conventional liquid-phase aptasensors. The confined geometry raised the locally recovered concentration approximately 90-fold over passive settling and 7.2-fold over active bulk suction, with EIS-derived estimates closely matching plate counts (EIS-to-plate ratios of 96–109%). Target recognition rather than non-specific particle loading governed the signal. Non-target bacteria and mineral dust yielded minimal responses, while sequential chamber scenarios resolved target introduction, mixed-species loading, and ventilation-driven clearance as discrete endpoints. Although current quantification thresholds and benchtop readouts necessitate further engineering, integrating the bioreceptor directly into the aerosol impaction surface establishes a compact, culture-free route for rapid bioaerosol monitoring.