Additive Strategies to Mitigate Humidity Interference Effects on PEDOT:PSS Sensors for Ammonia Detection

Abstract

Development of precise and accurate ammonia sensors suitable for healthcare (point-of-care devices) and environmental monitoring is imperative and absolute necessity. However, a persistent challenge in the gas sensor technology is sensitivity degradation due to humidity interference. To address this challenge, this study presents a screen-printed, flexible, and disposable sensor based on poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) mixed with additives having reduced humidity interference tailored for ammonia (NH3) gas detection. Polar solvents such as ethylene glycol (EG), dimethylformamide (DMF), and dimethyl sulfoxide (DMSO) are used as additives with the base material PEDOT:PSS. Enhanced hydrophobicity is confirmed via contact angle measurements. Current-voltage (I–V) characteristic assessments reveal a linear ohmic behavior, emphasizing the heightened conductivity of the samples with additives compared to the PEDOT:PSS sensor. When assessing the humidity response, the DMF-modified PEDOT:PSS sensor exhibited minimal % response, registering only 37.01% at 90% humidity. This was a marked improvement over the pristine PEDOT:PSS sensor, which recorded 118.5% at the same humidity level, and outperformed other additive variants. Regarding ammonia detection, the PEDOT:PSS/DMF sensor demonstrated an experimental detection ability up to 0.1 ppm with 0.91% response and outperformed the ammonia sensing ability of pristine PEDOT:PSS. Effect of relative humidity (~5%RH–80%RH) on ammonia gas sensing performance of PEDOT:PSS/DMF sensor is also conducted and compared with pristine PEDOT:PSS. The increment in sensor conductivity with rising ammonia concentrations is theorized due to the charge transfer, where ammonia’s lone pair of electrons interacts with the covalent backbone of PEDOT:PSS, suggesting a plausible sensing mechanism.