<p>With people today spending most of their time in indoor environments, it is important to monitor indoor air quality (IAQ) to better serve human health and safety protocols. Therefore, developing sensing devices to better monitor the potential of hazardous gases in the air is critical. There are various types of indoor pollutants that can be harmful to a person’s health, such as volatile organic compounds (VOCs) and flammable refrigerants. These gases originate from sources such as the decomposition of building materials; damaged heating, ventilation, and air conditioning (HVAC) units; cellular respiration of an overpopulated building; and leaks from gas powered homes. As such, researchers have developed small, lightweight sensors such as microelectromechanical systems (MEMS) that allow for real-time detection of gases to be implemented in IAQ monitoring. MEMS sensors have shown great promise as they are a highly sensitive and selective for a target gas analyte, are able to detect at room temperature, and are inexpensive to manufacture. However, most MEMS are highly dependent on the chemical recognition layer used. The thesis will highlight my work in the development of next-generation chemical recognition layers for gravimetric MEMS that are utilized in the detection carbon dioxide, formaldehyde, and hydrogen. For carbon dioxide, a polymer blend of polyethylene imine (PEI) and polyethylene oxide (PEO) was implemented as the chemical recognition layer. The blending of semicrystalline PEO into PEI caused a phase separation in which the materials morphology became highly porous. This microstructure allowed for detection of carbon dioxide down to 5 ppm. For formaldehyde sensing, a blend of poly-5-carboxyindole (P5C) and beta-cyclodextrin (β-CD) nanoparticles were used as a chemical recognition layer. The β-CD moieties helped to buffer the P5C to enhance the hydrogen bonding of the carboxylic acid associated with P5C. This allowed for detection of formaldehyde to concentrations as low as 25 ppm. In the hydrogen sensing devices, ultrathin palladium nanosheets (PdNS) were employed as a chemical recognition layer. The nanosheets were composed of monoatomic layers with 0.23 nm spacing. The tight uniformity and small pore size of the PdNS allowed for the detection of hydrogen as low as 1% in concentration. Furthermore, this document will briefly discuss areas where MEMS could have improvements to their sensitivity and selectivity towards a target gas analyte. These areas include improvements to material processing, filter encapsulation, and device modification.</p>