Space-time acoustofluidic tweezers for dynamic and selective manipulation of microparticles

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.