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A hybrid thin film is fabricated by a simple drop-casting method. Functionalized single-walled carbon nanotubes (SWCNTs) and gold nanoparticles (AuNPs) with a diameter of ≈15 nm are drop-casted onto a printed circuit board (PCB) substrate equipped with interdigitated electrodes. The addition of AuNPs to the carbon nanotube networked films enhance sensitivity and lower the detection limit to low parts-per-billion (ppb) concentrations. The gold particle to carbon nanotube ratio is optimized to find the optimum gold nanoparticle loading. The composite films were tested in both air and nitrogen environments across a wide relative humidity range (0-97%), which is suitable for dissolved Nitric Oxide (NO) detection in sea water for oceanographic study and for human breath analysis in medical diagnosis. The sensors exhibited high selectivity, particularly to NO, outperforming other tested gases. Notably, the sensor reliably detected NO at 10 ppb levels with response times within 10 seconds and recovery time around 1 minute, showcasing excellent reproducibility across sensors and operational efficiency within diverse humidity conditions.

The technology is a solid state, Carbon Dioxide (CO2) sensor configured for sensitive detection of CO2 having a concentration within the range of about 100 Parts per Million (ppm) and 10,000 ppm in both dry conditions and high humidity conditions (e.g., > 80% relative humidity). The solid state CO2 sensor achieves detection of high concentrations of CO2 without saturation and in both dynamic flow mode and static diffusion mode conditions. The composite sensing material comprises Oxidized Multi-Walled Carbon Nanotubes (O-MWCNT) and a metal oxide, for example O-MWCNT and iron oxide (Fe2O3) nanoparticles. The composite sensing material has an inherent resistance and corresponding conductivity that is chemically modulated as the level of CO2 increases. The CO2 gas molecules absorbed into the carbon nanotube composites cause charge-transfer and changes in the conductive pathway such that the conductivity of the composite sensing material is changed. This change in conductivity provides a sensor response for the CO2 detection. The solid state CO2 sensor is well suited for automated manufacturing using robotics and software controlled operations. The solid state CO2 sensor does not utilize consumable components or materials and does not require calibration as often as conventional CO2 sensors. Since the technology can be easily integrated into existing programmable electronic systems or hardware systems, the calibration of the CO2 sensor can be automated.