Recent advances in conducting polymer chemiresistive sensors for ammonia gas detection: materials, characterization, and applications

Abstract Conducting polymers (CPs) are highly susceptible to ammonia ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>NH</mml:mi> <mml:mn>3</mml:mn> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> ) at room temperature. This has spurred growing interest in CP-based <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>NH</mml:mi> <mml:mn>3</mml:mn> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> gas sensors across diverse fields, ranging from biomedicine to environmental monitoring. Detecting <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>NH</mml:mi> <mml:mn>3</mml:mn> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> levels in breath, from parts per million to parts per billion, aids in diagnosing health conditions like liver and kidney dysfunction. Despite the importance of CP-based <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>NH</mml:mi> <mml:mn>3</mml:mn> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> sensors, a comprehensive assessment of their performance, limitations, and prospects has yet to be conducted. To address this gap, this work provides a detailed review of chemiresistive <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>NH</mml:mi> <mml:mn>3</mml:mn> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> sensors based on CPs (including P3HT, PEDOT, PPy, and PANI), examining sensor response, selectivity, stability, repeatability, and sensitivity to environmental factors like humidity and temperature. The role of porous structures and gas diffusion mechanisms in enhancing CP sensor performance is emphasized, alongside CP-based composite materials. The mechanical flexibility of these sensors is analyzed and compared, highlighting their potential for integration into flexible and wearable devices. Key challenges for CP-based <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>NH</mml:mi> <mml:mn>3</mml:mn> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> sensors include poor selectivity due to interference from similar gases, sensitivity loss caused by humidity-induced CP swelling, and instability from temperature fluctuations. Additionally, the lack of standardized testing protocols complicates performance comparisons of CP-based <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>NH</mml:mi> <mml:mn>3</mml:mn> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> sensors. Future research should focus on improving CP porosity, understanding gas-CP interactions, developing stable composites, and exploring new CPs for improved <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>NH</mml:mi> <mml:mn>3</mml:mn> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> sensing.