Monitoring dissolved carbon dioxide (CO₂) in aquatic and sediment systems is critical for understanding carbon cycling and climate feedback. This study develops and characterizes a compact, low-cost microbolometer-based attenuated total reflectance (ATR) mid-infrared sensor for direct dissolved CO₂ measurement in liquid and soil-water environments. The system integrates a ZnSe ATR crystal with custom suspended SiN membrane microbolometers and uses evanescent-wave absorption at 4.26 μm with a broadband LED source and computational spectral reconstruction, eliminating the need for an interferometer. Calibration shows excellent linearity (R² ≈ 0.99) over 50–1000 ppm CO₂, with a practical limit of detection (LOD) of ~26–35 ppm at 5–25 °C. UV-induced CO₂ generation from soil-water mixtures was investigated across UV wavelengths, revealing UV-C (254 nm) as optimal, producing net ΔCO₂ ≈ 339 ppm above ambient levels in 30 min. Environmental factors (temperature 5–35 °C, pH 5–11, pressure 1–1.5 ATM, dissolved organic carbon) were systematically evaluated, confirming robust sensor performance (accuracy >90%, correlation r > 0.98 with reference instrument). This sensor represents the first integration of MEMS microbolometer detectors with ATR evanescent-wave spectroscopy for liquid-phase dissolved CO₂, enabling real-time monitoring and rapid sediment organic carbon assessment in a field-deployable platform.

This paper presents the design, fabrication, and characterization of a sub-milliwatt graphene-based micro thermal conductivity detector (µTCD) that utilizes a suspended multilayer graphene (MLG) bridge to sense volatile organic compounds (VOCs) in the gas phase based on their thermal transport properties. The graphene bridge is transferred onto a silicon chip with integrated microchannels using a photolithography-free process. By incorporating microchannel designs, this approach enables precise transfer of suspended MLG dimensions without conventional patterning steps. A key innovation of this work lies in the use of an ultra-low thermal mass suspended graphene architecture, which significantly increases temperature rise per unit input power, thereby enhancing sensitivity per unit power compared to conventional metal-based TCDs. The fabricated µTCD successfully produces chromatograms of multiple VOC species, closely matching those obtained using a standard flame ionization detector (FID). The device demonstrates an estimated limit of detection (LOD) of 190 ppm while consuming an average power of 151 µW under DC operation.

We present a new palladium-based nanogap hydrogen sensor designed for fast, low-concentration H₂ detection in environmental monitoring applications. The device consists of a long electrically-conductive low-stress palladium cantilever beam separated by a nanometer-sized air gap from a second cantilever beam of different length placed near the first beam tip thus forming a H₂-dependent capacitor. The cantilevers are anchored on top of a thermally-isolated SiN membrane with an integrated microheater that maintains the sensor at constant temperature. When exposed to H₂, the capacitor nanogap is reduced resulting in a change in capacitance with H₂ sensitivity $S_{\mathrm {H2}} =0.15$ fF/ppm. The sensor shows a consistent response up to $55~^{\circ }$ C with a thermal drift smaller than 0.22 aF/^oC and a minimum detectable signal of 10 ppm. The device repeatability was confirmed across 5 consecutive test cycles. Selectivity tests show negligible response to common interfering gases CO, CO₂, CH₄, water vapor and NH₃ ( $S_{i}\lt 5.2\times 1{0}^{-6}$ fF/ppm). The sensor exhibited a response time of approximately 390 ms upon exposure to H₂.[2025-0141]

This letter presents a uniform 5-nm Pd-Au nanogap sensor, fabricated using a batch-fabrication wafer-scale process, enabling sub-ppm hydrogen (H2) detection for operating at room temperature with ultra-low-power operation in an in-field-deployable sensor node. The nanogap sensor was integrated into a compact size of 58 × 52 mm 2 that combines a Pd-Au nanogap sensor, signal processing unit, and wireless communication unit, while all units being powered by a coin cell battery (220 Ah). The nanogap sensor unit operates in a normally off mode, consuming 12 pW in standby, while the complete system including processing and communication units consumes 51.40 µW. Upon detecting ≥0.46 ppm H2, the Pd layer expands to close the nanogap, switching the node on to an active the state to wirelessly transmit detection alerts. This wake-up operation reduces average power consumption to 67.84 µW with one detection event per week, supporting up to 59 weeks of operation. At 1 ppm of H2, the sensor shows a response time of ≤5 seconds for detection and a recovery time of ≤3 minutes for resetting, thus, multiple H2 leak measurements can be achieved. The development of this compact Pd-Au nanogap sensor node is expected to advance the safety of H2 transportation and storage infrastructure where even sub-ppm levels of highly flammable H2 gas leaks is concerned.