Sonication is a process in which ultrasonic are used to agitate particles in solution. Such disruptions can be used to mix solutions, speed the dissolution of a solid into a liquid (like sugar into water), and remove dissolved gas from liquids.

         Sound is a wave made up of alternating regions of high and low pressure.  Imagine yourself as a particle.  As a sound wave passes you, you experience moments of high pressure (like at the bottom of a hill of a roller coaster when you feel pressed into your seat) separated by periods of low pressure (like at the top of a hill of a roller coaster when you feel ‘weightless’).  The frequency of a sound wave is a measure of how often the particles of a substance vibrate (how quickly you transition from the ‘top’ feeling to the ‘bottom’ feeling of a roller coaster).   The sound waves used in sonication are usually ultrasound waves with frequencies above what you can hear (above 20 kHz that is 20,000 cycles per second) and as frequency increases the strength of the agitation increases.

       In solution, the particles vibrate because as they experience cycles of pressure, microscopic vacuum bubbles form and then collapse into solution, a process called cavitation. These vibrations can disrupt molecular interactions (e.g. between molecules of water), break clumps of particles apart, and lead to mixing.  In the case of dissolved gas, these vibrations can allow the gas bubbles to come together and more easily leave the solution.²  

Sonicators either produce sound waves into a water bath, where samples are placed, or can be probes that are put directly into the sample to be sonicated.  Such a machine will be used in the third part of this experiment to prepare the bead solution for application to the biosensor.