An Absorption-Based PDMS/f-CNT Mass-Capacitor for Continuous Monitoring of Fire-Derived Organic Contamination

Firefighters are exposed to complex smoke containing volatile, semivolatile, aromatic, and particulate-associated organic contaminants that accumulate on skin, clothing, and protective equipment. Conventional gas sensors monitor only selected airborne species, while passive samplers require laboratory analysis and cannot provide continuous exposure assessment. To address this limitation, we developed a proof-of-concept mass-capacitor that integrates contaminant absorption and electrical sensing within a single polydimethylsiloxane/functionalized carbon nanotube (PDMS/f-CNT) composite coated on interdigitated electrodes (IDEs). Unlike conventional sensors that report the instantaneous concentration of selected compounds, the proposed platform functions as both a sorptive collector and an electrical transducer. It continuously converts contaminant uptake, retention, and release into a time-resolved electrical response. For firefighter applications, this mass-capacitor bridges the gap between passive sorptive samplers and conventional real-time gas sensors. It enables continuous tracking of the cumulative sorbed contamination burden without requiring offline laboratory analysis or restricting the measurement to selected airborne species. A custom potentiostat applied staircase cyclic excitation, while Fast Fourier Transform (FFT)-assisted processing enabled extraction of the differential charge, ΔQ as an indicator of contaminant loading. The sensor was evaluated using smoke generated from cotton, paper, wood, and synthetic fibers. Compared with PDMS alone, the PDMS/f-CNT composite produced an approximately 24-fold higher response with minimal humidity interference (≈80% RH). Limits of detection ranged from 0.08 to 0.26 ppm, while repeated smoke exposures produced stepwise increases in ΔQ, demonstrating continuous tracking of cumulative contaminant loading. These results establish the feasibility of the mass-capacitor concept and introduce a new approach for real-time monitoring of the accumulated organic contamination burden rather than the instantaneous concentration of individual airborne compounds.