Investigation on a novel photoacoustofluidic effect

Abstract

Acoustic manipulation of micro-objects (particles, cells, and bacteria) can be achieved using ultrasonic standing waves in a fluidic or microfluidic resonator. By matching resonator dimensions and acoustic field frequency, it is possible to use acoustic radiation force (ARF) to gather the particles in the pressure nodal (or anti-nodal) plane, creating one or several aggregates. In standard operating conditions, they can be maintained as long as needed in acoustic levitation at this equilibrium position. In this study, we present a new unexpected phenomenon. After creating a large aggregate of light-absorbing particles, we show that it is possible to force the complete breakup of the aggregate when we enlighten it with an electromagnetic wave of adequate wavelength and intensity. If the particles remain in acoustic levitation, they are quickly rejected and propelled away from the aggregate leading to its fast destruction. We show that this phenomenon strongly depends on both the amplitude of the ultrasonic field and the intensity of the lighting. Various experiments with different types of particles and concentrations are used to discuss the possible explanations of the phenomenon. Moreover, investigations showed that this phenomenon applies to biological compounds such as red blood cells and stem cells, suggesting potential biomedical applications.