Gelatin Methacryloyl (GelMA) hydrogels are widely utilized in biomedical applications due to their biocompatibility and tenable mechanical properties. Traditional methods for measuring stiffness are often destructive, which limits real-time monitoring of critical processes such as swelling and cell growth. Here, Surface Acoustic Wave (SAW) sensing is employed to characterize the mechanical properties of GelMA hydrogels with varying concentrations and degrees of functionalization. GelMA samples were fabricated and subjected to compression testing alongside SAW measurements to assess stiffness via wave attenuation. While mass load affects wave reflection linearly, wave attenuation is an exponential response and the primary influence on stiffness measurements, with SAW sensing yielding greater reproducibility than compression testing. This indicates enhanced reliability and sensitivity in measuring dynamic property changes. Rayleigh-SAW technology has been successfully applied to 3D hydrogels, enabling real-time monitoring of cellular behavior and supporting advances in tissue engineering and other biomedical applications. Overall, SAW sensing offers a promising alternative to traditional mechanical testing, enhancing our ability to analyze complex biological systems.

Recent advances and challenges of manipulation of micro- and nanoparticles by surface acoustic wave in microfluidics

We perform three-dimensional simulations of SAW-driven spreading of silicone oil drops on flat substrates and over solid obstacles. The resulting model takes the form of a three-dimensional long-wave thin-film equation incorporating capillary, gravitational, and SAW-induced acoustic stresses. A key feature of the formulation is a smooth attenuation function that localizes acoustic forcing within the bulk drop while avoiding spurious transverse discontinuities. Comparisons with results of earlier 2D formulations demonstrate qualitatively similar dynamics, albeit the additional spatial dimension permits transverse mass redistribution driven by capillarity, which leads to slower streamwise spreading and slightly lower drop apexes than predicted by 2D models. The model is applied to SAW induced dynamic wetting of flat substrates and solid obstacles and is representative of experimental geometries. Quantitative comparisons with experimental observations show good agreement for front propagation and obstacle climbing dynamics. In particular, improved agreement with the experimentally observed dependence of the liquid climbing time over obstacles on SAW amplitude is obtained when the fully three-dimensional formulation is used.

We report the development of a sensitive biosensing platform based on a shear-horizontal surface acoustic wave (SH-SAW) device and paper fluidics, with the potential to be used outside centralized laboratory settings. Systematic research on the biorecognition surface, blocking agent, fluidics and measuring unit allowed us to transform a laboratory-based method into a field-deployable device. As a proof-of-concept, the platform was used for the detection of SARS-CoV-2 anti-spike antibodies on a surface-immobilized spike protein, tested in both simulated and human blood serum samples. A poly-L-lysine (PLL) layer was selected as a biocompatible surface for spike protein immobilization; the polymer layer can be easily removed through gentle mechanical rubbing, allowing regeneration and multiple uses of the sensing device. This surface, combined with novel paper-based capillary fluidics, enabled real-time monitoring of spike antibody binding via acoustic wave phase measurements in the range of 1-100 nM antibodies in 1% v/v serum. Further acoustic wave amplitude amplification and a tenfold improvement in the detection limit (0.1 nM) were achieved by the use of gold nanoparticles conjugated with a secondary antibody. This optimized assay was successfully evaluated in a small pilot clinical study of 20 patient samples. Our new SH-SAW immunosensor exhibited sensitivity and specificity comparable to commercial systems with standard fluidics and instrumentation; importantly, its limit of detection is better than the clinically relevant value of ∼11 RU mL-1. This portable, low-cost platform, combining a pocket-size network analyzer with disposable paper fluidics and a regenerable sensing surface, offers a promising solution for quantitative antibody detection near or at the point-of-care.

Fluorescence-activated cell sorting (FACS) is fundamental for single-cell analysis, but conventional systems often require free-space optical alignment and high-rate analog acquisition. Here, we present an integrated acoustofluidic sorter that combines focused traveling surface acoustic wave (FTSAW) actuation, an on-chip fiber-optic interface, and event-level digital photon counting. By operating at a 10 kHz sampling frequency, our software-defined acquisition scheme substantially reduces the real-time data burden compared to analog reconstruction methods, all while maintaining a high signal-to-noise ratio exceeding 23 dB. The system achieves 93.8% purity for sorting fluorescent microspheres at a theoretical throughput of up to 2 kHz. Furthermore, we demonstrated its practical utility by separating Haematococcus pluvialis from Chlorella vulgaris with 92.6% purity, while preserving high membrane integrity and short-term metabolic activity. By integrating the optical fibers into the chip and using photon-counting acquisition, the system reduces optical alignment requirements and lowers the acquisition burden for sorting control. These features may provide a practical basis for developing compact and easier-to-operate single-cell analysis platforms.

The convergence of surface acoustic wave technology and artificial intelligence.

Skyrmions, as nonlinear topological solitons, have garnered significant attention due to their unique physical properties and promising potential for applications. However, achieving controlled manipulation of skyrmion arrays remains a formidable challenge. Here, we introduce a SAW-mediated strategy to engineer well-ordered skyrmion configurations within ferromagnetic [Co/Pd]n multilayer nano-islands. We exploit radially propagating SAWs generated by fan-shaped interdigital transducers to achieve controlled spatial ordering of skyrmions. The ordering arises from SAW-induced anisotropic strain gradients, which create periodically modulated potential landscapes. Quasi-static analysis reveals the critical role of magnetoelastic coupling, enabling strain-amplitude-dependent lattice transitions and wavelength-selective ordering. Furthermore, pulsed SAWs implement a neuromorphic synapse-inspired design emulating long-term potentiation, achieving 94.6% accuracy on CIFAR-10. This work not only provides an effective strategy for controlling skyrmion arrangement in confined nano-islands but also offers valuable insights for the device integration of skyrmions.

GHz-range surface acoustic waves (SAWs) are essential for high-frequency sensing, hybrid photonic-phononic, and quantum devices. However, SAW generation via interdigital transducers (IDTs) on piezoelectric substrates faces significant scaling and attenuation challenges, besides being incompatible with silicon-based electronics due to the lack of piezoelectricity. Here, we demonstrate fundamental and higher-order SAW generation and detection in monolithic silicon using metallic transducers and time-resolved extreme ultraviolet diffraction measurements. Our results, supported by finite-element simulations, establish the equivalence of first- and second-order SAW frequencies (ν) and attenuation lifetimes (τS) over wide ranges spanning 3.5-16.5 GHz and 14-0.6 ns, respectively, that allow high-frequency SAW generation with large τS in the same device. We further show that τS is tunable via transducer geometry, achieving second-order SAWs (2ν) near 10 GHz with τS ≈ 5 ns. These findings reveal lower acoustic losses in silicon than those reported with IDTs on piezoelectric substrates.

Three-dimensional multiphysics modeling of size-selective microparticle separation driven by focused traveling surface acoustic waves

The orbital Hall effect, which generates orbital currents, has emerged as a key mechanism for the angular momentum transport in solids. Its acoustic analogue, the acoustic orbital Hall effect, has recently been observed in which a surface acoustic wave (SAW) drives an orbital current transverse to its propagation direction. However, their microscopic mechanism has remained elusive. Here, we reveal that the acoustic orbital Hall effect in Ti is driven by an acoustoelectric mechanism. Using Ti/Ni bilayers on a piezoelectric LiNbO3 substrate, we observe a clear phase shift in the magnetic field angle dependence of the acoustic orbital Hall voltage as the SAW propagation direction is varied relative to the crystallographic axes. This behavior is consistent with orbital current generation by the in-plane electric field associated with the acoustoelectric evanescent wave. Moreover, from simultaneously measured acoustic orbital Hall and acoustic orbital pumping signals, we determined the efficiency of converting lattice dynamics into orbital transport.

Biofouling presents numerous challenges across various sectors, including aquaculture, agriculture, infrastructure, and medicine. The development of anti-biofouling techniques remains a significant challenge. In the water industry, biofouling on monitoring sensors substantially compromises the accuracy of measurements by interfering with the sensors’ measuring ability. Biofouling also significantly increases the running costs by increasing the frequency of maintenance needed to keep sensors clean and accurate. Consequently, anti-biofouling techniques are widely employed to clean in situ optical sensors, ensuring accurate measurements while minimizing overall system costs. The conventional approach for preventing biofouling from in situ sensors typically involves the application of coatings, mechanical brushes, ultraviolet radiation, and ultrasonic waves, which possess distinct advantages and disadvantages contingent upon their application. The challenges associated with protecting the small windows of water quality sensors from biofouling over extended periods using current methods are either expensive or adversely affect the integrity of monitoring data. This study introduces a low-cost centimeter-scale high-frequency surface acoustic wave (SAW) device to protect the small windows of in situ water quality sensors continuously from biofouling, functioning as an auxiliary anti-biofouling mechanism. This study found that this 16 MHz SAW device can mitigate the formation of biofilms by adhesive diatom strains CS-1664, CS-1665, and by planktonic algae CS-327 by approximately 98% in comparison to control conditions, functioning effectively as an anti-biofouling tool for itself and surrounding surfaces without adversely affecting aquatic organisms. The dimension and resonance frequency (RF) of the SAW device are also capable of being fabricated according to the area requiring cleaning. A miniaturized 16 MHz SAW device can sustain operation for prolonged periods up to a couple of months without maintenance, at a low cost and power consumption, providing a new anti-biofouling technology. This methodology aims to assist the Australian inland and coastal water quality monitoring system by reducing maintenance costs while simultaneously enhancing the longevity of sensors submerged in water for extended periods.

We demonstrate an acousto-optic sensing approach that integrates a dual-core As2Se3 nanofiber interferometer within a surface acoustic wave (SAW) cavity to achieve externally driven intermodal phase modulation distinct from spontaneous forward Brillouin scattering. Introducing a thin liquid coupling layer allows Rayleigh SAW to satisfy the leaky wave condition causing radiation into the liquid, converting into a leaky SAW, enabling modulation sidebands and narrow detection bandwidths approaching the Hz level. Interferometric sensitivity is improved through coherent detection with balanced receivers and polarization biasing, acting as a common-mode noise rejection system, minimizing the optical noise floor to within ∼1 dB of the photodetector dark-noise limit.

Detection of cyanobacteria MC-LR using modulated surface acoustic wave (SAW) sensor for enhanced sensitivity, selectivity and limit of detection

High-precision wide-range temperature measurement by annular interdigital transducer-based surface acoustic wave sensors

Coherent control of the nitrogen-vacancy (NV) center in diamond is commonly achieved by microwave fields from conventional antennas, which suffer from scalability and thermal noise. Their spatially extended field profiles also limit their specificity in driving one NV spin without affecting other NV spins. Here, we investigate quantum control of a single NV center with microwave fields generated from a nanoscale magnet that is proximal to the NV center. Our results show nanoscale coherent control with high contrast Rabi oscillations using nearfield microwaves from shape anisotropic nanomagnets of lateral dimensions down to 200 , driven by surface acoustic wave (SAW) excitation. Furthermore, we show that varying the acoustic power driving such nanomagnets can achieve control over Rabi frequency. We also report spin-spin relaxation time () of the NV center, measured up to 3.480.01 μs using microwave pulses generated by such nanomagnets. The use of the nanoscale magnets to implement highly localized coherent quantum control can replace thermally noisy microwave circuits and demonstrate a path to scalable quantum computing and sensing with NV-defects in diamond and other spin qubits.

Multi-parameter controlled acoustofluidic assembly of colloidal and cellular structures.

Optical ultrasound detection enables greater miniaturization than conventional piezoelectric transducers while preserving high sensitivity. Although sub-micron silicon photonics detectors have been demonstrated, image artifacts caused by surface acoustic waves interference remain a key challenge. Polymer detectors offer better acoustic coupling, yet they have been limited to tens of micrometers in size because of optical confinement requirements. Here we overcome that limit with the smallest polymer resonator built on an optical fiber, using a 6 µm thick polymer cavity on a tapered single mode fiber tip. The detector achieved a bandwidth of about 150 MHz and a noise equivalent pressure density of about 1.5 mPa.Hz-1/2. Imaging experiments yielded 7 µm axial and 17 µm lateral resolution, with high fidelity performance that surpassed piezoelectric and state of the art optical detectors. This combination of broad bandwidth, artifact free imaging, and manufacturability makes the detector ideal for optoacoustic mesoscopy (OptAM) applications.

High-sensitivity cantilever beam-type surface acoustic wave stress-strain sensor

Electrical isolation is critical to ensure safety and minimize electromagnetic interference (EMI), yet existing methods struggle to simultaneously transmit power and signals through a unified channel. Here we demonstrate a mechanically-isolated gate driver based on microwave-frequency surface acoustic wave (SAW) device on lithium niobate that achieves galvanic isolation of 2.75 kV with ultralow isolation capacitance (0.032 pF) over 1.25 mm mechanical propagation length, delivering 13.4 V open-circuit voltage and 44.4 mA short-circuit current. We demonstrate isolated gate driving for a gallium nitride (GaN) high-electron-mobility transistor, achieving a turn-on time of 108.8 ns and validate its operation in a buck converter. In addition, our SAW device operates over an ultrawide temperature range from 0.5 K (-272.6 °C) to 544 K (271 °C). The microwave-frequency SAW devices offer inherent EMI immunity and potential for heterogeneous integration on multiple semiconductor platforms, enabling compact, high-performance isolated power and signal transmission in advanced power electronics.

Label-free and effective sorting of red and white blood cells based on their physical properties is crucial for subsequent single-cell analysis or immune cell engineering applications. However, cell sorting relying on the physical effects of one single physical property remains highly challenging. This paper proposes a cell sorting method based on a focused traveling surface acoustic wave (FTSAW)-based acoustofluidic chip, which leverages the ability of FTSAW acoustofluidics to comprehensively respond to multiple physical characteristics of cells (e.g., size, density, morphology, and deformability), and furthermore allows for precise setting of the action area range and adjustment of the action intensity. In experiments, a pair of focused interdigital transducers (FIDTs, characteristic frequency: 128.6 MHz) on the substrate of lithium niobate and a typical microchannel structure (single-side sheath flow focusing followed by bifurcated sorting, i.e., "two streams merging into one and then splitting into two") were designed and fabricated. Parameter optimization experiments for separation and sorting were conducted on 3 μm and 5 μm polystyrene (PS) beads, as well as red and white blood cell samples after sheath flow focusing. The results indicate that the FTSAW-based acoustofluidic chip enabled white blood cell sorting with high purity (∼90%) and high biological viability (∼98%). This study demonstrates the potential of the FTSAW-based acoustofluidic chip for cell sorting. Owing to its easy integration and advantages (non-contact operation, no sieve pore clogging, broad compatibility with cell culture media), it is expected to serve as a key pre-processing technology in microfluidic systems for single-cell analysis or cell engineering.