Over the past decade, MEMS microhotplate devices have been developed at the National Institute of Standards and Technology to support semiconductor metal oxide films for use in conductometric gas sensor arrays. In most cases, the materials have been based on compact thin films of SnO2 or TiO2 deposited by single-source precursor chemical vapor deposition. Of particular interest to our group is the enhancement of the sensitivity of the microsensors to trace gas species by inducing nanostructured porosity and large internal surface areas in the films. In this presentation, we discuss the development of nanostructured sensor materials based on porous TiO2 nanoparticle thin films. The preparation and evaluation of pure and Nb-doped TiO2 nanoparticle films are described. The films on the MEMS microhotplate substrates are evaluated as conductometric gas sensors based on the critical performance elements of sensitivity, stability, speed and selectivity. The sensor performance, and specifically the sensitivity, of the novel nanoparticle TiO2 films is compared with that of traditional compact CVD-derived films.