Acoustophoresis devices are proposed as tools for manipulation and diagnostic in microfluidic environments. We demonstrate that their diffusion can be supported and enhanced by Digital Holography. Indeed, this technique covers all the current imaging needs and can stimulate the development of novel applications thanks to its unique features. The numerical refocusing is exploited to control the manipulation during acoustic focusing and acoustic-driven aggregation and to retrieve the 3D trajectories of tracer beads for the ultrasound field calibration. Besides tracking, DH displays its full potential when USs are used to directly manipulate or deform cells. In this case, numerical processing provides information on the sample movement and morphology, with potential applications in the field of diagnostic.
KEYWORDS: Particles, 3D image processing, Microfluidics, Holography, Digital holography, Microscopy, Lab on a chip, Phase imaging, Acoustics, Holograms, Ultrasonography, Automatic tracking, Digital image correlation and tracking, Real time imaging
We demonstrate a 3D holographic tracking method to investigate particles motion in a microfluidic channel while unperturbed while inducing their migration through microfluidic manipulation. Digital holography (DH) in microscopy is a full-field, label-free imaging technique able to provide quantitative phase-contrast. The employed 3D tracking method is articulated in steps. First, the displacements along the optical axis are assessed by numerical refocusing criteria. In particular, an automatic refocusing method to recover the particles axial position is implemented employing a contrast-based refocusing criterion. Then, the transverse position of the in-focus object is evaluated through quantitative phase map segmentation methods and centroid-based 2D tracking strategy. The introduction of DH is thus suggested as a powerful approach for control of particles and biological samples manipulation, as well as a possible aid to precise design and implementation of advanced lab-on-chip microfluidic devices.
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