Mitigation of Humidity Interference in Colorimetric Sensing of Gases

Abstract

Colorimetric sensing technologies have been widely used for both quantitative detection of specific analyte and recognition of a large set of analytes in gas phase, ranging from environmental chemicals to biomarkers in breath. However, the accuracy and reliability of the colorimetric gas sensors are threatened by the humidity interference in different application scenarios. Though substantial progress has been made toward new colorimetric sensors development, unless the humidity interference is well addressed, the colorimetric sensors cannot be deployed for real-world applications. Although there are comprehensive and insightful review articles about the colorimetric gas sensors, they have focused more on the progress in new sensing materials, new sensing systems, and new applications. There is a need for reviewing the works that have been done to solve the humidity issue, a challenge that the colorimetric gas sensors commonly face. In this review paper, we analyzed the mechanisms of the humidity interference and discussed the approaches that have been reported to mitigate the humidity interference in colorimetric sensing of environmental gases and breath biomarkers. Finally, the future perspectives of colorimetric sensing technologies are also discussed.

Humidity-Independent Artificial Olfactory Array Enabled by Hydrophobic Core–Shell Dye/MOFs@COFs Composites for Plant Disease Diagnosis

“…Volatile organic compounds (VOCs) monitoring and detection is of great importance and applied in diverse fields such as disease diagnosis, − environmental monitoring, and the quality assessment of food and beverages. , Among a variety of VOCs detection technologies, the colorimetric sensor array has been one of the most emerging ways due to rapidity, cost-effectiveness, and portability. − Inspired by the mammalian olfactory system, the colorimetric sensor arrays take advantage of the cross-reaction between colorants and analyte mixtures to generate a visual fingerprint pattern. − While colorimetric sensor arrays have been extensively studied, few have been commercialized for some limitations, such as humidity-dependent sensitivity. , Humidity refers to the amount of water vapor in the air, ranging from 6280 ppm (20% relative humidity, RH) to 25 740 ppm (80% RH) in ambient air. , In general, the concentration of water vapor is much higher than that of gas analytes at the ppm or ppb level in ambient air. Thus, the humidity interference is a huge challenge to the colorimetric sensor arrays for VOCs detection in the field of practical application.…”

“…11−14 While colorimetric sensor arrays have been extensively studied, few have been commercialized for some limitations, such as humidity-dependent sensitivity. 11,15 Humidity refers to the amount of water vapor in the air, ranging from 6280 ppm (20% relative humidity, RH) to 25 740 ppm (80% RH) in ambient air. 16,17 In general, the concentration of water vapor is much higher than that of gas analytes at the ppm or ppb level in ambient air.…”

Azobenzene/Acid Binary Systems for Colorimetric Humidity Sensing with Reversibility, High Sensitivity, and Tunable Colors

“…It also has potential applications in our daily life such as the real-time monitoring of respiration for athletes and patients, detection of certain diseases, weather forecasting, and air-conditioning monitoring of buildings. − The importance of humidity sensors has instigated much interest in designing devices based on variation of physical, chemical, and microstructural properties upon humidity change. Various types of humidity sensors, such as electronic humidity sensors, , optical fiber humidity sensors, − and colorimetric humidity sensors, − are classified based on their operating principles using capacitive, resistive, gravimetric, and optical properties . Despite various advantages of electronic and optical fiber humidity sensors, the complex fabrication process and the relatively high cost of electronic and optical components and equipment limit their scope of commercial applications .…”

Alginate-based hydrogels embedded with ZnO nanoparticles as highly responsive colorimetric oxygen indicators

“…26 The water in the hydrogels facilitates the dissolution of volatile gases such as CO 2 or total volatile basic nitrogen from fresh meat products, resulting in a visible color change in pH sensitive indicators that monitor food freshness and spoilage. [27][28][29] Humidity has been shown to both physically and chemically interfere with gas sensors that utilize different sensing platforms 13,30 such as semiconductor metal oxide sensors, 31 electrochemical sensors, 32 and optical sensors including colorimetric sensors. 33 However, some colorimetric chemical reactions can be accelerated by water vapor to increase sensitivity and reduce the response time of the sensor.…”