Devices, systems and methods for measuring and detecting properties of a variety of particles or cells in suspension. Properties, such as, for example, velocity of particles, concentration and/or size may be measured according to the methods of the invention. Acoustic energy may be introduced to a focal zone and narrow band interrogating signals may be used. The acoustic energy may cause movement or streaming of the fluid or suspension. The acoustic streaming may allow a Doppler effect measurement without any other source of velocity.