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Cell selective manipulation with single beam acoustical tweezers

Acoustical tweezers open major prospects in microbiology for cells and microorganisms contactless manipulation, organization and mechanical properties testing since they are biocompatible, label-free and can exert forces several orders of magnitude larger than their optical counterpart at equivalent wave power. Yet, these tremendous perspectives have so far been hindered by the absence of selectivity of existing acoustical tweezers -- i.e., the ability to select and move objects individually -- and/or their limited resolution restricting their use to large particle manipulation only. Here, we report precise selective contactless manipulation and positioning of human cells in a standard microscopy environment, without altering their viability. Trapping forces of up to $\sim$ 200 pN are reported with less than 2 mW of driving power. The unprecedented selectivity, miniaturization and trapping force are achieved by combining holography with active materials and fabrication techniques derived from the semi-conductor industry to synthesize specific wavefields (called focused acoustical vortices) designed to produce stiff localized traps. We anticipate this work to be a starting point toward widespread applications of acoustical tweezers in fields as diverse as tissue engineering, cell mechano-transduction analysis, neural network study or mobile microorganisms imaging, for which precise manipulation and/or controlled application of stresses is mandatory.