Single-walled carbon nanotube (SWCNT) networks are synthesized using porous silica as the catalyst supporting material. Structural and spectroscopic analyses show that the tailored catalyst-support interactions enable us to effectively control the morphology and density of high-quality SWCNT networks. Preliminary gas- and bio-sensing tests based on these networks demonstrate unprecedented sensitivity and stability towards a variety of gases (such as NH3 and NO2) and biomarkers (such as prostate specific antigen). Such sensing properties are further improved by uniformly decorating metal nanoparticles onto the SWCNT networks through plasma modification. In addition, changing the type of carbon feedstock in the synthesis process can transform the sparse, randomly-entangled networks to the densely packed, vertically aligned arrays, whose porous structure and large surface area can serve as another promising sensing platform. Our findings enable the controlled synthesis of multifunctional SWCNTs, which is highly desirable for many applications.