Holographic imaging of erythrocytes in acoustofluidic platforms

Acoustofluidics exploits ultrasounds and microfluidic platforms to achieve label-free and contactless manipulation of micro sized objects. Here, we demonstrate the use of off-axis digital holography to investigate the behavior of erythrocytes dispersed in water and exposed to ultrasound standing waves. We consider two different regimes of manipulation. In the first case, the sample is stilled inside the microfluidic channel. Under the influence of acoustic forces, the cells move to the first nodal plane, where they start an aggregation process. We follow the formation of clusters in different regions of the channel, highlighting the different structures that emerge. As a second regime, we monitor the axial position of cells flowing during the application of ultrasuonds. By using a resonance frequency that originates multiple nodal positions, we show how holographic imaging can be used to image the cells distributed in the different nodes.