A simplified three-dimensional numerical simulation approach for surface acoustic wave tweezers

Numerical and experimental study of circular array to enhance acoustic tweezer-based particle manipulation

Acoustic tweezers enable non-contact, non-invasive manipulation, with promising applications in fields such as biology, micromechanics, and advanced materials. The circular array, commonly used to generate acoustic vortices-an important type of acoustic tweezer-consists of multiple independently addressable elements arranged in a circular configuration. By adjusting the element excitations, the circular array can flexibly control the location of particles. In this study, we employed numerical and experimental methods to analyse the relationship between device geometrical parameters and acoustic field distribution, as well as their impact on particle manipulation. Results from the three-dimensional model indicate that water surface height, array radius, and the material and thickness of the bottom observation layer, significantly influence the acoustic field distribution and, hence trapping performance. Additionally, we used trap stiffness theory to evaluate particle movement capability, and experimentally identified conditions under which trapping may fail, providing theoretical support for improving acoustic tweezer technology.

A Review of SAW-Based Micro- and Nanoparticle Manipulation in Microfluidics

Surface acoustic wave (SAW)-based microfluidics has emerged as a promising technology for precisely manipulating particles and cells at the micro- and nanoscales. Acoustofluidic devices offer advantages such as low energy consumption, high throughput, and label-free operation, making them suitable for particle manipulation tasks including pumping, mixing, sorting, and separation. In this review, we provide an overview and discussion of recent advancements in SAW-based microfluidic devices for micro- and nanoparticle manipulation. Through a thorough investigation of the literature, we explore interdigitated transducer designs, materials, fabrication techniques, microfluidic channel properties, and SAW operational modes of acoustofluidic devices. SAW-based actuators are mainly based on lithium niobate piezoelectric transducers, with a plethora of wavelengths, microfluidic dimensions, and transducer configurations, applied for different fluid manipulation methods: mixing, sorting, and separation. We observed the accuracy of particle sorting across different size ranges and discussed different alternative device configurations to enhance sensitivity. Additionally, the collected data show the successful implementation of SAW devices in real-world applications in medical diagnostics and environmental monitoring. By critically analyzing different approaches, we identified common trends, challenges, and potential areas for improvement in SAW-based microfluidics. Furthermore, we discuss the current state-of-the-art and opportunities for further research and development in this field.

Enhanced integrated acoustofluidics with printed circuit board electrodes attached to piezoelectric film coated substrate

The current key issues in applying acoustofluidics in engineering lie in the inflexibility of manufacturing processes, particularly those involving modifications to piezoelectric materials and devices. This leads to inefficient prototyping and potentially high costs. To overcome these limitations, we proposed a technique that is capable of prototyping acoustofluidic devices in a straightforward manner. This is achieved by simply clamping a printed circuit board (PCB) featuring interdigital electrodes (IDEs) onto a substrate coated with a piezoelectric thin film. By applying appropriate clamping force between the PCB and the substrate, one can effectively generate surface acoustic waves (SAWs) along the surface of the substrate. This approach simplifies the prototyping process, reducing the complexity and fabrication time. The clamping mechanism allows for easy adjustment and optimization of the SAW generation, enabling fine-tuning of the fluid and particle manipulation capabilities. Furthermore, this method allows for customizable interdigital transducers (IDTs) by 'patterning' IDEs on thin-film piezoelectric substrates (such as ZnO/Al and ZnO/Si) with various anisotropy orientations. This facilitates the on-demand generation of wave modes, including A0 and S0 Lamb waves, Rayleigh waves, and Sezawa waves. One notable advantage of this method is its capability to rapidly test acoustic wave patterns and performance on any substrate, offering a fast and streamlined approach to assess acoustic behaviors across diverse materials, thereby paving the way for efficient exploration of novel materials in SAW technology.

A smartphone serves as a data logger for a fully automated lab-constructed microfluidic system

Fluorescence is an innovative technique that has captivated scholars in recent years due to its superior sensitivity and selectivity. The development of microfluidic components has added to its appeal, particularly given the technology ability to control fluid using very small quantities (microliter range) and achieve high liquid throughput. We have combined these two technologies to develop a lab-constructed simple system for measuring fluorescence, notable for the following features:•The device constructed entirely in our lab and programmed for measuring the fluorescence of liquids using microfluidic technology, delivered excellent results. The regression coefficient R² (0.9995) was obtained five points between 0.001-0.01µg .ml-1. Moreover, the reproducibility standard deviation (%) of 0.008 µg .ml-1 fluorescein dye remained at zero, for ten repeated experiments.•The device was full automated using a smartphone as a data logger, and lab-constructed programs.•The results were satisfactory with a detection limit of 1 × 10-4 µg.ml-1. This proposed system can measure over 200 samples per hour making it highly efficient and eco-friendly due to the reduced use of reagents and lower waste production. The fully automated system can effectively be used to determine fluorescein dye concentrations. Another application (micro pump view) manages all actions required in this microfluidic system, such as operating the two lab-constructed peristaltic pumps.

Investigation on submicron particle separation and deflection using tilted-angle standing surface acoustic wave microfluidics

With the development of in vitro diagnostics, extracting submicron scale particles from mixed body fluids samples is crucial. In recent years, microfluidic separation has attracted much attention due to its high efficiency, label-free, and inexpensive nature. Among the microfluidic-based separation, the separation based on ultrasonic standing waves has gradually become a powerful tool. A microfluid environment containing a tilted-angle ultrasonic standing surface acoustic wave (taSSAW) field has been widely adapted and designed to separate submicron particles for biochemical applications. This paper investigated submicron particle defection in microfluidics using taSSAWs analytically. Particles with 0.1-1 μm diameters were analyzed under acoustic pressure, flow rate, tilted angle, and SSAW frequency. According to different acoustic radiation forces acting on the particles, the motion of large-diameter particles was more likely to deflect to the direction of the nodal lines. Decreasing the input flow rate or increasing acoustic pressure and acoustic wave frequency can improve particle deflection. The tilted angle can be optimized by analyzing the simulation results. Based on the simulation analysis, we experimentally showed the separation of polystyrene microspheres (100 nm) from the mixed particles and exosomes (30-150 nm) from human plasma. This research results can provide a certain reference for the practical design of bioparticle separation utilizing acoustofluidic devices.

Numerical Study of Particle Separation through Integrated Multi-Stage Surface Acoustic Waves and Modulated Driving Signals

The manipulation of biomedical particles, such as separating circulating tumor cells from blood, based on standing surface acoustic wave (SSAW) has been widely used due to its advantages of label-free approaches and good biocompatibility. However, most of the existing SSAW-based separation technologies are dedicated to isolate bioparticles in only two different sizes. It is still challenging to fractionate various particles in more than two different sizes with high efficiency and accuracy. In this work, to tackle the problems of low efficiency for multiple cell particle separation, integrated multi-stage SSAW devices with different wavelengths driven by modulated signals were designed and studied. A three-dimensional microfluidic device model was proposed and analyzed using the finite element method (FEM). In addition, the effect of the slanted angle, acoustic pressure, and the resonant frequency of the SAW device on the particle separation were systemically studied. From the theoretical results, the separation efficiency of three different size particles based on the multi-stage SSAW devices reached 99%, which was significantly improved compared with conventional single-stage SSAW devices.

Three-dimensional modeling and experimentation of microfluidic devices driven by surface acoustic wave

Surface acoustic wave (SAW) technology is proving to be an effective tool for manipulating micro-nano particles. In this paper, we present a fully-coupled 3D model of standing SAW acoustofluidic devices for obtaining particle motion. The "improved limiting velocity method" (ILVM) was used to investigate the distribution of acoustic pressure and acoustic streaming in microchannel. The results show that the distribution of acoustic pressure and acoustic streaming on the piezoelectric substrate surface perpendicular to the acoustic wave propagation direction is inhomogeneous. The motion of micro-particles with diameters of 0.5-, 5-, and 10 μm is then simulated to investigate the interaction of acoustic radiation force and drag force caused by pressure and acoustic streaming. We demonstrate that micro and nanoparticles can move in three dimensions when acoustic radiation force and acoustic streaming interact. This result and method are critical for designing SAW microfluidic chips and controlling particle motion precisely.