Increased sensitivity of diagnostic latex agglutination tests in an ultrasonic standing wave field

A technique is described which increases the sensitivity of latex agglutination tests for soluble and particulate antigens. The levels of detection of tests for C-reactive protein and E. coli O157 respectively have been improved by x256 and x1024 compared with the standard test procedure of sample rotation on a test-card. This new method combines dilution of the test latex particles, a 2 min sample treatment in the ultrasonic standing wave field of a tubular piezo-electric transducer and subsequent examination by video-microscopy. Ultrasonic treatment is required to achieve increased localised concentrations of the latex particles in the standing wave field, and dilution of the latex is a critical requirement to allow agglutination to occur at low antigen concentrations.