Biomolecule-nanoparticle (NP) hybrid systems provide functional assemblies for the construction of sensors, nanocircuitry and devices. The development of sensors based on functionalized NPs will be exemplified with the electrical contacting of glucose oxidase with Au NPs (1.4 nm) functionalized with the FAD cofactor, and with the optical detection of telomerase activity in cancer cells using CdSe-ZnS core-shell NPs. Also, the formation of shaped Au NPs exhibiting longitudinal red-shift absorbance will be used to follow NAD⁺-dependent biocatalytic reactions. The use of biomolecule-NP hybrid systems for nanocircuitry and devices is addressed by the polymerization of Au-NPs functionalized G-actin followed by the catalytic enlargement of the filaments to generate continuous, conductive Au-nanowires. Sequential polymerization of Au-NP-modified G-actin and G-actin yields patterned nanowires with motor functions. The immobilization of the filaments on a myosin interface results in the motility of the filaments upon addition of the ATP fuel. The nano-objects move on the surface at a speed corresponding to 250 nm·sec^-1. [DOI: 10.1380/ejssnt.2005.1]