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Biotech labs detect the activity of antibodies by labelling them with fluorescent chemicals that glow when the antibody binds to an antigen. But the marker can alter the behaviour of the molecules under study, so Autonomics APS of Copenhagen suggests a sound alternative (WO 03/100413). The test materials are placed on a flat surface between a piezoelectric sound generator and a detector. As the sound waves travel through the test materials, any larger molecules formed when antibodies bind to antigens create a telltale shift in the waves’ frequency.