Phosphate buffered saline (PBS, 1x) was prepared in ultra-pure water (resistivity > 18 MΩ cm) containing 137 mM, 2.7 mM KCl, 10.1 mM Na2HPO4 2H2O, and 1.8 mM KH2PO4 and adjusted to pH 7.4 with HCl and NaOH solutions (0.5, 1, and 5 M). The virus dilution buffer (VDB) was prepared by adding 5mM NaH2PO4•2H2O and 10mM NaCl in ultra-pure water. The pH of the buffer was adjusted to 7.0 using NaOH and HCl.