All-silica microfluidic optical stretcher with acoustophoretic prefocusing

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Acoustophoresis is a widely reported and used technique for microparticle manipulation and separation. In the study described here, acustophoresis is employed to prefocus the flow (i.e., focusing occurring upstream of the analysis region) in a microfluidic chip intended for optical trapping and stretching. The whole microchip is made of silica with optical waveguides integrated by femtosecond laser writing. The acoustic force is produced by driving an external piezoelectric ceramic attached underneath the microchip at the chip resonance frequency. Thanks to an efficient excitation of acoustic waves in both water and glass, acoustophoretic focusing is observed along the channel length (>40 mm) and it is successfully demonstrated both with polystyrene beads, swollen red blood cell, and cells from mouse fibroblast cellular lines (L929). Moreover, by comparing results of cell stretching measurements, we demonstrate that acoustic waves do not alter the optical deformability of the cells and that the acoustic prefocusing results in a considerable enhancement of throughput in optical stretching experiments.

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We acknowledge financial support from COST action MP1205 for two short-term scientific missions of GN to DTU as well as Fondazione Cariplo through the Grant “Optofluidic chips for the study of cancer cell mechanical properties and invasive capacities” (Ref. # 2011-0370). In addition, we acknowledge enlightening discussions with Peter Barkholt Müller and Henrik Bruus, and we thank Livia Visai and Nora Bloise for the L929 cells growth, preparation, and suspension.

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Correspondence to Giovanni Nava.

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Nava, G., Bragheri, F., Yang, T. et al. All-silica microfluidic optical stretcher with acoustophoretic prefocusing. Microfluid Nanofluid 19, 837–844 (2015).

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  • Optical stretcher
  • Acoustic prefocusing
  • Femtosecond laser micromachining