The HIV retrovirus, in particular, is a single-stranded RNA virus that duplicates itself in a host cell by converting its genetic code into double-stranded DNA that is then inserted into the host cell.
To Dr Baselt this suggested that tiny magnetic particles might be attached to molecules using either antibodies (which will bond to proteins, sugars and so on) or single-stranded DNA (which will bond to a complementary DNA strand to form the famous double helix).