A separator disk for use in centrifugal separation of components is designed to automatically position itself during separation at the interface between the supernatant and the remaining components. The reagents include a replicable genetic package, a protein displayed on an exterior surface of the package that is expressed from a heterologous nucleic acid borne by the package, and one or more antibodies complexed with the expressed protein and which have an open binding site for a target protein. The single-crystal silicon layer constitutes a channel region, a source region, and a drain region. Novel strategies for detecting HCMV are also disclosed.