Ultrasonic manipulation of locomotive microorganisms and evaluation of their activity

Acoustic manipulation of locomotive microorganisms, i.e., euglena and paramecia, was conducted by using ultrasonic standing waves of ∼3 MHz. Microorganisms were trapped at the intersections of the nodes in the two orthogonal standing waves and were transferred horizontally and vertically by the suitable ultrasonic frequency change. Aggregation of microorganisms was also observed in the process of the cyclic frequency change. The trapping efficiency depended on both ultrasonic power density and the activity of microorganisms. The effects of water temperature and illumination on their activity were evaluated by measuring the ultrasonic trapping efficiency.