Figure 1.

Single-bubble (SB) and two-bubble (TB) acoustic tweezing cytometry (ATC). (a) Experimental setup of ATC using oblique or vertical ultrasound application. (b) Schematics of pARF and the attractive sARF exerted on two microbubbles. (c and d) Brightfield images showing one (c) or two (d) microbubbles attached to single cells (NIH 3T3 fibroblasts in c; hMSCs in d). (e) Brightfield images and line plot showing the temporal evolution of the lateral displacement of a single bubble attached to an NIH 3T3 fibroblast subjected to ATC. The incident angle of the ultrasound is 45° with respect to the vertical direction. (f) Brightfield images and line plot of lateral displacements of a pair of microbubbles subjected to TB-ATC. The incident angle of the ultrasound is 0° with respect to the vertical direction. Insets in e and f: bubble displacements during the first ultrasound pulse. (g) Pseudo-color images showing the contractile force of single NIH 3T3 fibroblasts measured by the micropost technique before and 30 min after TB-ATC application. The TB-ATC application lasted 10 s from t = 0 min. Yellow arrows point to integrin-bound microbubbles. (h) Change of total CSK contractile force for single cells (relative to contractility before ultrasound) with bubbles (n = 9) and without microbubbles (+US/−MB, n = 5) subjected to 10 s TB-ATC application. (i and j) Accumulative displacements of bubbles and contractile force changes divided by the acoustic pressure. Ultrasound parameters: frequency 1.25 MHz, acoustic pressure 0.05 MPa (SB-ATC) or 0.015 MPa (TB-ATC), pulse duration 50 ms, and PRF 1 Hz. Error bars, mean ± SE. ^∗∗p < 0.01, Student’s t-test. To see this figure in color, go online.