Here we controllably generate and rapidly characterize hybrid structures composed of inorganic particles and viruses. Nano and mesostructured materials and modular assemblies promise to improve interfaces between biomolecular and inorganic components for tissue engineering, novel therapeutics, cancer treatments, and microelectronics. Realization of these goals requires reliable methods to produce, characterize, and tune the component building blocks. Here we advance towards this vision by combining a gold nanoparticle and a viral particle into a chemically specific heterodimer, which we characterize using electrospray differential mobility analysis (ES-DMA). The advantages of ES-DMA are that it requires no labeling, provides a direct read-out of particle size distributions, rapidly measures statistically significant populations of viruses, allows the extraction of kinetic rate constants from temporal variation, and detects changes in virus size as little as 0.2 nm. The use of phage display libraries may open this technique to an entire family of nanoparticle-virus clusters. This talk will describe the theory of operation of ES-DMA and its use to size viruses, inorganic nanoparticles and their composites.