Particle aggregation method and apparatus

An apparatus for carrying out an immuno-agglutination assay, said apparatus comprising:

• a tube for containing a liquid sample in which particles potentially susceptible to agglutination are suspended, such that said sample is formed with an upper and a lower boundary within said tube, said lower boundary forming a meniscus;
• a tubular ultrasound transducer positioned to encircle said tube;
• means to excite said tubular ultrasound transducer to generate a standing wave ultrasound field within said tube and so expose said sample to said standing wave field for a predetermined period, said standing wave field extending radially of said tube and exhibiting a progressive change in pressure amplitude radially within said tube so that, in use of said apparatus, said particles suspended in said liquid sample are displaced radially of said tube to aggregate at least one predetermined annular region;
• and
• means to inspect said particles of said sample after termination of said predetermined period, wherein said particles settle towards said meniscus to determine whether said particles remain aggregated or whether they disperse.