Dynamic acoustofluidics enables precise, contact-free manipulation of particles, colloids, and cells and shows great potential for applications in physics, materials science, and life sciences. However, existing strategies struggle to realize contrast-based selective manipulation primarily because the pressure fields are time invariant. Here, we introduce a space-time acoustofluidic tweezer (STAT) that uses frequency detuning-induced pseudo-space-time modulation of standing surface acoustic waves to enable dynamic, contrast-dependent control of microparticles and cells. Experiments and simulations show that, under STAT manipulation, positive (PACP) and negative (NACP) acoustic contrast particles can undergo low-frequency, shear- and longitudinal-like harmonic motions, respectively. Under certain driving conditions, NACPs can be selectively guided along programmed paths, whereas PACPs remain stably patterned. Overall, STAT offers a gentle, biocompatible way to selectively drive oscillation, transport, and sorting among particles and cells of different acoustic contrasts, broadening the capabilities of acoustofluidic systems for biomedical applications.
WU et al. (2026) studied this question.