Direct quantification of unadsorbed viruses in suspensions of adsorbing colloids with the enzyme-linked immunosorbent assay

Quantification of two plant viruses in suspensions of homoionic Ca-bentonite was conducted by applying to the enzyme-linked immunosorbent assay plates either the virus-clay mixture (direct method) or the supernatant obtained after the clay was allowed to settle (classic method). Both methods showed a similar dependence of free virus content on clay concentration. A higher content at equilibrium was measured for both viruses by the direct method. The advantage of using the direct over the classic method is discussed.