See this example properly formatted in the QUT Cite tool.
Professor R. Collins stated in a personal conversation on April 16, 2014, that…
It was confirmed that this organism was present by Professor R. Collins … (Personal interview, April 16, 2014).
There is nothing to be included in a reference list, as these materials cannot be traced by the reader.
Name the person, his/her title, the type of communication (e.g. email, letter) and the date.