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.
Acoustophoresis devices are popular tools for manipulation and diagnostic in microfluidic environments. They offer the opportunity for contactless manipulation of cells. We demonstrate that the combination of acoustic manipulation and holographic imaging provides a suitable system for the simultaneous handling and of biological matter. We employ an acoustofluidic device with a transparent piezo element, to enable optical investigation through the channel. The holographic imaging is thus employed to observe and analyze the behavior of Red Blood Cells during the application of ultrasound radiation. The flexible refocusing, and quantitative phase imaging of single cells and RBCs clusters is reported.
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.
In global healthcare and point-of-care diagnostics there is an increasing request of medical equipment with devices able to provide fast and reliable testing for clinical diagnosis. In developing countries that lack of adequate facilities, this need is even more urgent. Lab-on-a-Chip devices have undergone a great growth during the last decade, supported by optical imaging techniques more and more refined. Here we present recent progresses in developing imaging tools based on holographic microscopy that can be very useful when applied into bio-microfluidics. Digital Holography (DH) is label-free, non-invasive, potentially high-throughput and, above all, quantitative. We show the recent advancements of DH in transmission microscopy mode, when this is applied to microfluidics to yield 3D imaging capabilities. Holographic flow cytometry through quantitative phase imaging and in-flow tomography for the analysis and manipulation of micro-particles and cells will be shown [1-3]. Medical diagnostic applications based on DH will be also shown. Moreover, we present a portable common-path holographic microscope embedded onboard a microfluidic device that paves the way to the application of DH on the field [4].
KEYWORDS: Holography, Microfluidics, Diffraction gratings, Holograms, Digital holography, Microscopy, Diffraction, Lab on a chip, Optical design, Imaging systems
The diffusion of miniaturized analysis platforms has spurred the development of portable and compact imaging systems. We present a compact, lens-based imaging module that implements wavefront division off-axis holography on a commercial microfluidic chip, thanks to the insertion of a diffraction grating. The initial architecture is realized in three configurations. Different positioning of the grating respect to the microfluidic channel (parallel and orthogonal) are explored, and an enhancement of the imaging system compactness and price-effectiveness is realized by further functionalizing the chip with micro-optics. The three configurations are separately analyzed and tested. It is demonstrated that the characteristic features of Digital Holography, i.e. label-free imaging, quantitative phase mapping and flexible refocusing, are preserved, and differences and specific fields of applicability are highlighted.
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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