This letter proposes a coaxial stub microfluidic impedance transformer and discusses its design, theory, and operation. Electrostatically-stabilized colloidal dispersions using non-aqueous fluids facilitate its electromagnetic agility by altering their effective medium properties. Theoretical, simulated, and measured results at 400 MHz, 800 MHz, and 1.6 GHz using 0%, 25%, and 50% volume fractions of colloidal Barium Strontium Titanate dispersed in a low-loss severely hydrotreated mineral oil are included to demonstrate the operation of the device. Simulated results for non-spherical nanoparticles are included to show the potential of different material systems. \ 2006 IEEE.