Recent work demonstrates that nanoparticle surface conductivity is sensitive to surface adsorption of counter-ions and charged molecules. Nanoparticles are already used in many molecular assays because of the sensitivity offered by their size-to-volume ratio and because, with their large number, they speed up the mass-transfer limiting reaction by reducing the required transport time. We demonstrate fast label-free DNA hybridization and ELISA detection on nanocolloidal substrates using dielectrophoresis, and discuss the current work and future studies in developing colloid based biological assays in microfluidic devices.