Advances in acoustic tweezers for biological detection: from mechanisms to applications

Acoustic tweezers use acoustic radiation force and acoustic streaming generated by ultrasound fields to achieve contactless and relatively low-damage manipulation of biological targets, including cells, bacteria, extracellular vesicles, and other micro-/nanoscale objects. In biosensing workflows, they mainly function as modules for sample preparation, target enrichment, sorting, reaction organization, and mass-transfer enhancement before downstream signal readout. This review summarizes the fundamental mechanisms, representative device configurations, and integration strategies of acoustic tweezers, with emphasis on how their analytical roles change with target scale. Radiation-force-based focusing and sorting are most effective for cells and bacteria, whereas nanoscale targets increasingly require localized streaming, interfacial acoustic fields, microbubble oscillation, or vortex-based manipulation; molecular assays mainly benefit from enhanced mixing, mass transfer, and droplet organization. Recent applications are evaluated according to the analytical bottleneck addressed, quantitative performance improvement, sample conditions, and remaining limitations. Acoustic tweezers are further compared with optical tweezers, dielectrophoresis, magnetic manipulation, inertial microfluidics, and deterministic lateral displacement using common workflow-level criteria. They offer a balanced combination of label-free operation, biocompatibility, throughput, and microfluidic integration, but are not universally superior in precision or nanoscale control. Clinical translation remains limited by force-streaming competition, complex-matrix field distortion, acoustic heating, device-to-device variation, cross-talk with downstream readout, and insufficient validation in minimally processed clinical samples. Future efforts should focus on scale-specific multiphysics design, closed-loop workflow integration, standardized manufacturing and reporting, and clinically defined validation to advance acoustic tweezers from laboratory prototypes toward deployable point-of-care testing systems.