Flexible Chemiresistive Chitosan-Glycerol Sensors on Laser-Induced Graphene Electrodes for Room-Temperature Ammonia Detection

We report a metal-free sensor platform combining laser induced graphene (LIG) electrodes with drop-deposited, glycerol-plasticized chitosan biopolymer formulations for sustainable, chemiresistive detection of ammonia at room temperature. Increasing the glycerol v/v concentration from 2.5% to 7% yielded a logarithmic reduction (>400-fold) in baseline device resistance (R₀) at 60% RH. Devices fabricated using 5% glycerol showed chemiresistive response, ΔR/R₀ = −16% ± 1% (n = 4) at 79 ppm NH₃ (∼60% RH) with linear range 5–45 ppm and limit of detection ∼6–8 ppm. Chitosan-LIG devices showed excellent selectivity for ammonia over other volatile organic compounds (VOCs), with concentration-normalized responses for ammonia exceeding those of other VOCs by factors of 25–80. Devices showed minimal hysteresis (<2% cycle-to-cycle variation); good repeatability (ΔR/R₀∼19% ± 1.5% at 79 ppm; 20 cycles), and excellent stability over six weeks (R₀ = 3.41–3.53 MΩ, ΔR/R₀ = −8% ± 2%, for 18 ppm NH₃. Flexibility tests (1500 cycles) showed ≤20% baseline drift and <3% variation in ΔR/R₀, highlighting the potential for future flexible or wearable devices. Finally, proof-of-concept monitoring in high-humidity environments (∼85% RH), showed chemiresistive signatures for fish spoilage, with ΔR/R₀ ∼ −46% ± 14% for devices mounted above ∼20 g fish in 5 mL water vs. ΔR/R₀ ∼+21% ± 10%, for reference devices (water only).