A sensitive and economical method to directly detect particles

We have developed a sensitive and economical method to directly detect particles. The technique, which we term rupture event scanning (REVS), is based on rapidly oscillating a surface to which a particle has been attached. This can be achieved with an acoustic wave device, such as a quartz crystal micro-balance (QCM), coated with particle-specific protein or chemical receptors. As the magnitude of oscillation of the surface is increased, there is increasing acceleration of adherent particles. This in turn results in a larger force exerted by the surface on the particle that ultimately causes rupture of the bonds attaching the particle to the surface. The same piezoelectric device can be used as a very sensitive microphone to detect the acoustic emission produced by bond rupture, which is then converted into an electrical signal. The signal indicates not only the presence of the particle and its affinity for the receptor, but also the number of particles present. The method works in air, water and complex biological fluids, is quantitative over at least six orders of magnitude of particle titer, and in affinity from sub-mM to pM. Sensitivity is in the order of fg/mm/sup 2/ (10/sup -15/ g/mm/sup 2/) and the entire assay currently takes less than one hour to perform.