A Tunable 50 MHz Acoustic Vortex Tweezers for Size-Selective Manipulation and Cell Pre-concentration

Abstract

In microfluidic bioanalysis, efficient target manipulation, enrichment, and sample pretreatment are key bottlenecks. Although high-frequency ultrasound (>50 MHz) can provide tens of micrometers resolution and enable precise non-contact manipulation, existing solutions have fixed focal points, single manipulation modes, and high acoustic attenuation in the acoustic field regulation, making them difficult to achieve higher frequencies. These limit their flexibility and precision in complex analyses. Here, we introduce a tunable 50 MHz acoustic vortex tweezers based on a low attenuation silicon metasurface. Unlike traditional fixed-focus transducers, this device uses topological charge modulation (M=1, 3, 5) to adjust the capture orbit diameter, ranging from 50 to 150 μm. Manufactured using deep reactive ion etching (DRIE) on monocrystalline silicon, the metasurface ensures lower energy loss and higher structural resolution compared to traditional polymer vortex devices. We demonstrate its multiple application modes: orbital rotation and size-selective manipulation of microparticles, as well as customized range pre-concentration of cells. This device creates a "protective cage" with a low-pressure core that has a variable range, allowing cells to aggregate into clusters. This silicon-based vortex platform is compatible with semiconductor processes, providing a universal label-free solution for biological sample analysis and high-sensitivity downstream detection in lab-on-chip systems.