We report on the deployment of MEMS static bifurcation (DC) sensors for the detection of volatile organic compounds (VOCs): hydrogen sulfide and formaldehyde. We demonstrate a sensor that can detect as low as a few ppm of hydrogen sulfide. We also demonstrate a sensor array that can selectively detect formaldehyde in the presence of benzene, a closely related interferent. Toward that end, we investigate the sensitivity and selectivity of two detector polymers—polyaniline (PANI) and poly (2,5-dimethyl aniline) (P25DMA)—to both gases. A semiautomatic method is developed to functionalize individual sensors and sensor arrays with the detector polymers. We found that the sensor array can selectively sense 1 ppm of formaldehyde in the presence of benzene.

Once a promising polymeric (detection) material is identified, it needs to be incorporated into a MEMS sensor. In this sensor functionalization step, the deposition of the polymeric material on the sense‐plate should be accurate and repeatable. After a quick overview of different deposition methods and related solubility characteristics of polyaniline (and derivatives), drop coating is implemented to deposit polyaniline on sense‐plates, moving from a manual deposition technique to a semi‐automated deposition procedure with more practical benefits, and identifying an optimal ‘carrier’ mixture of 10–15/90–85 polyaniline/ethylene glycol. A correlation can be established between area coverage and polymer mass, which leaves room for future fully automated deposition using image processing.

Polyaniline (PANI) and a polyaniline derivative (poly (2,5-dimethyl aniline)) are evaluated for their sensitivity towards formaldehyde. Among the two polymer backbones evaluated, polyaniline seems more sensitive towards formaldehyde. Therefore, to further enhance sensitivity towards formaldehyde, polyaniline is doped with different weight percentages of indium oxide and further evaluated for its sensing capabilities such as sensitivity, selectivity, and stability. It is found that PANI with 1.25 wt% of In 2 O 3 is most sensitive towards formaldehyde, while PANI with 5 wt% of In 2 O 3 is most selective towards formaldehyde over benzene interferent. It is observed that sensitivity and selectivity trends for PANI doped with different wt% of In 2 O 3 are reverse of each other. All sensing materials are found stable. Introduction and BackgroundVolatile organic compound (VOC) detection is important for health and environmental protection. [1] The long VOC list also includes formaldehyde (F), benzene (B), acetone (A), ethanol (E) and acetaldehyde (Ac), which can be present indoors and outdoors. Exposure to even low concertation of VOCs can cause discomfort in the eyes, nose and throat, shortness of breath, nausea, and headaches. Exposure to high concentrations can cause damage to the liver, kidneys, and nervous system. Formaldehyde (F) has been extensively used in the manufacturing of plastics and resins. [2] It is used as a disinfecting and preservative agent on a daily basis both at the industrial and domestic levels. It is a common indoor and outdoor toxic organic pollutant. [3,4] Formaldehyde is also responsible for the sick building syndrome. [5,6] Exposure to formaldehyde can cause irritation in eyes, nose, throat, and skin, and can lead to harmful and chronic respiratory problems in the long term. Therefore, it is important to be able to detect formaldehyde present in the surroundings.Several techniques have been explored in the literature for developing a reliable sensor for formaldehyde detection.