Membrane filters and other modern devices are used to isolate and identify viruses by separating them from host cells. While a larger pore size, such as ${}5\text{ }\mu\text{m}$, blocks only the largest particles, a filter pore size of ${}200\text{ nm}$ (${}0.2\text{ }\mu\text{m}$) physically removes larger microbes like bacteria, allowing the smaller virions to pass through and be collected in the filtrate.