A process for capturing or concentrating microorganisms for detection or assay comprises (a) providing a concentration agent that comprises diatomaceous earth bearing, on at least a portion of its surface, a surface treatment comprising a surface modifier comprising titanium dioxide, fine-nanoscale gold or platinum, or a combination thereof; (b) providing a sample comprising at least one microorganism strain; and (c) contacting the concentration agent with the sample such that at least a portion of the at least one microorganism strain is bound to or captured by the concentration agent.