In a recent article, we described how environmental DNA (eDNA) has been used to detect the presence of aquatic species in lakes and rivers. eDNA studies have demonstrated great potential for surveillance of rare, endangered, and invasive species by simply collecting and analyzing water samples from target habitats. Dr. Caren Goldberg, of Washington State University, is one researcher using a unique combination of Sterlitech filters in her investigations of Yangtze giant softshell turtles in southeast Asia, tiger salamanders in California and Arizona, and fairy shrimp in southern California.
Many of our eDNA end-user researchers utilize disposable filter funnels for this application. These are convenient, presterilized single-use vacuum holders that contain 0.45µm rated mixed cellulose esters (MCE) membrane filters. This membrane material is great for retaining very small particles potentially holding eDNA; however, the small pore size posed a problem for Dr. Goldberg, as her lake and wetland samples often had sediment that would cause the filters to clog prematurely. Fortunately, these disposable funnels are designed with a removable filter. Normally the filters are removed after use for subsequent analysis, but this design feature also allows users to replace the filter before use to optimize the funnels for their applications. For example, Dr. Goldberg and her colleagues determined that 5.0µm rated Polyethersulfone (PES) membrane filters worked well for their water samples, allowing them to process larger volumes while still retaining target particles.
A fascinating aspect of eDNA studies is the wide diversity of the filters being used, as shown by Dr. Goldberg and others. Instead of the filters converging into one or two standard types, the filters being used are almost as diverse as the studies themselves; researchers have the freedom to select filters that are optimal for their studies.