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Apnoea, a major sleep disorder, affects many adults and causes several issues, such as fatigue, high blood pressure, liver conditions, increased risk of type II diabetes, and heart problems. Therefore, advanced monitoring and diagnosing tools of apnoea disorders are needed to facilitate better treatment, with advantages such as accuracy, comfort of use, cost effectiveness, and embedded computation capabilities to recognise, store, process, and transmit time series data. In this work we present an adaptation of our apnoea-Pi open-source surface acoustic wave (SAW) platform (Apnoea-Pi) to monitor and recognise apnoea in patients. The platform is based on a thin-film SAW device using bimorph ZnO and Al structures, including those fabricated as Al foils or plates, to achieve breath tracking based on humidity and temperature changes. We applied open-source electronics and provided embedded computing characteristics for signal processing, data recognition, storage, and transmission of breath signals. We show that the thin-film SAW device out-performed standard and off-the-shelf capacitive electronic sensors in terms of their response and accuracy for human breath-tracking purposes. This in combination with embedded electronics makes a suitable platform for human breath monitoring and sleep disorder recognition. HIGHLIGHTS: • An open-source system for sleep disorder monitoring is developed. • An embedded platform using SAW sensors achieves fast response and accuracy. • A proof-of-concept breath-tracking system is provided. [ABSTRACT FROM AUTHOR]

Surface acoustic wave (SAW) devices are increasingly applied in life sciences, biology, and point-of-care applications due to their combined acoustofluidic sensing and actuating properties. Despite the advances in this field, there remain significant gaps in interfacing hardware and control strategies to facilitate system integration with high performance and low cost. In this work, we present a versatile and digitally controlled acoustofluidic platform by demonstrating key functions for biological assays such as droplet transportation and mixing using a closed-loop feedback control with image recognition. Moreover, we integrate optical detection by demonstrating in situ fluorescence sensing capabilities with a standard camera and digital filters, bypassing the need for expensive and complex optical setups. The Acousto-Pi setup is based on open-source Raspberry Pi hardware and 3-D printed housing, and the SAW devices are fabricated with piezoelectric thin films on a metallic substrate. The platform enables the control of droplet position and speed for sample processing (mixing and dilution of samples), as well as the control of temperature based on acousto-heating, offering embedded processing capability. It can be operated remotely while recording the measurements in cloud databases toward integrated in-field diagnostic applications such as disease outbreak control, mass healthcare screening, and food safety. [ABSTRACT FROM AUTHOR]

Spatial distribution of biological cells plays a key role in tissue engineering for reconstituting the cellular microenvironment, and recently, acoustofluidics are explored as a viable tool for controlling structures in tissue fabrication because of its good biocompatibility, low‐power consumption, automation capability, nature of non‐invasive, and non‐contact. Herein, a reusable acoustofluidic device is developed using surface acoustic waves for manipulating microparticles/cells to form a 3D matrix pattern inside a scaffold‐based hydrogel contained in a millimetric chamber. The 3D patterned and polymerized hydrogel construct can be easily and safely removed from the chamber using a proposed lifting technique, which prevent any physical damages or contaminations and promote the reusability of the chamber. The generated 3D patterns of microparticles and cells are numerically studied using a finite‐element method, which is well validated by the experimental results. The proposed acoustofluidic device is a useful tool for in vitro engineering 3D scaffold‐based artificial tissues for drug and toxicity testing and building organs‐on‐chip applications. [ABSTRACT FROM AUTHOR]

Different acoustic wave modes are required for effective implementation of biosensing and liquid actuation functions in an acoustic wave-based lab-on-a-chip. For efficient sensing in liquids, shear waves (either a thickness-shear bulk wave or a shear-horizontal surface acoustic wave) can achieve a high sensitivity, without significant loss of acoustic wave energy. On the other hand, longitudinal bulk waves or out-of-plane displacement waves (such as Rayleigh waves) enable efficient sampling functions and liquid manipulation. However, there are significant challenges in developing a lab-on-a-chip to efficiently generate multiple wave modes and perform both these functions on a single piezoelectric substrate, especially when a single crystalline orientation is available. This paper highlights the latest progress in the theories and techniques to deliver both sensing and microfluidic manipulation functions using engineered inclined-angled piezoelectric films, allowing for the simultaneous generation of longitudinal (or Rayleigh) and thickness-shear bulk (or shear-horizontal surface acoustic) waves. Challenges and theoretical constraints for generating various wave modes in the inclined films and techniques to efficiently produce inclined columnar and inclined crystalline piezoelectric films using sputtering deposition methods are presented. Applications of different wave modes in the inclined film-based lab-on-chips with multiple sensing and acoustofluidic functions are also discussed. [ABSTRACT FROM AUTHOR]

Nanocrystalline ZnO films with strong (0002) texture and fine grains were deposited onto ultra-nanocrystalline diamond (UNCD) layers on silicon using high target utilization sputtering technology. The unique characteristic of this sputtering technique allows room temperature growth of smooth ZnO films with a low roughness and low stress at high growth rates. Surface acoustic wave (SAW) devices were fabricated on ZnO/UNCD structure and exhibited good transmission signals with a low insertion loss and a strong side-lobe suppression for the Rayleigh mode SAW. Based on the optimization of the layered structure of the SAW device, a good performance with a coupling coefficient of 5.2% has been realized, promising for improving the microfluidic efficiency in droplet transportation comparing with that of the ZnO/Si SAW device. An optimized temperature coefficient of frequency of −23.4 ppm °C−1 was obtained for the SAW devices with the 2.72 µm-thick ZnO and 1.1 µm-thick UNCD film. Significant thermal effect due to the acoustic heating has been redcued which is related to the temperature stability of the ZnO/UNCD SAW device. [ABSTRACT FROM AUTHOR]

Abstract: Love mode surface acoustic wave (SAW) ultraviolet (UV) sensors were fabricated through sputtering ZnO films on 36° Y-cut LiTaO3 substrate. Crystalline structure, morphology and photoluminescence (PL) of the sputtered ZnO films were characterized using X-ray diffraction, atomic force microscopy and fluorescence spectrometer. The PL spectra revealed that different defects in the ZnO films were dependent on the oxygen partial pressure during deposition. UV sensing measurements showed that at a power density of 350μWcm−2, the amplitude of the Love mode SAW UV sensor decreased up to −6.4dB with a frequency shift of ∼150kHz under a 254nm illumination. When this device was illuminated with 365nm UV light at 570μWcm−2, the amplitude of the transmission signal decreased only −2.5dB without any significant frequency shift. A frequency hopping effect during the downshift and recovery periods was identified due to the simultaneous interplays between the variations of the acoustic velocity and attenuation during the acoustic-electric interaction. [Copyright &y& Elsevier]

• Successfully integrated closed-loop control strategy into SAW device to build an acoustofluidic closed-loop control system. • Experimentally demonstrated the precise and reliable control of single microparticle in three-dimensional space. • System principle and biocompatibility are verified by the experimental tests on the breast cancer cells. • Experimentally demonstrated separation of larger size microparticles when being controlled at speed limit. Precise, automatic and reliable position control of micro-objects such as single particles, biological cells or bio-organisms is critical for applications in biotechnology and tissue engineering. However, conventional acoustofluidic techniques generally lack reliability and automation capability thus are often incapable of building an efficient and automated system where the biological cells need to be precisely manipulated in three dimensions (3D). To overcome these limitations, we developed an acoustofluidic closed-loop control system which is combined with computer vision techniques and standing surface acoustic waves (SSAWs) to implement selective, automatic and precise position control of an object, such as a single cell or microparticle in a microfluidic chamber. Position of the object is in situ extracted from living images that are captured from a video camera. By utilizing the closed-loop control strategy, the object is precisely moved to the desired location in 3D patterns or along designed trajectories by manipulating the phase angle and power signal of the SSAWs. Controlling of breast cancer cells has been conducted to verify the principle and biocompatibility of the control system. This system could be employed to build an automatic system for cell analysis, cell isolation, self-assembling of materials into complex microstructures, or lab-on-chip and organ-on-chip applications. [ABSTRACT FROM AUTHOR]

Metal element (Nb, Er, and Gd) doped WO x powders were prepared via a one-step solvothermal method to enhance photocatalytic property of WO x , and they were used to enhance ultraviolet (UV) sensing performance of ZnO/glass surface acoustic wave (SAW) devices. Results showed that Gd-doped WO x has a better photocatalytic performance amongst the other doped WO x (Nb and Er), which can be explained using the different reductions of band gaps after doping. Gd-doped WO x coated on the ZnO/glass SAW device demonstrates the best performance in enhancement of UV sensitivity which is 14 times higher than the uncoated SAW device. The incorporation of dopants Gd into the WO x matrix leads to a multitude of effects that collectively enhance the UV sensing performance, including modified band gap, increased charge carrier generation, enhanced conductivity, efficient charge separation, and recombination suppression. Electrical properties and UV sensing mechanisms on ZnO/glass SAW devices based on Gd-doped WO x were studied, and the frequency shifts in these SAW devices are primarily due to ultraviolet-induced changes in conductivity and thermal effects. [Display omitted] • An UV sensing technique was introduced using doped WO x layers as sensing layers based on SAW technology functions. • Qualitative and quantitative analysis on the UV sensing performance of doped WO x on ZnO/glass SAW device. • Exploration in the mechanisms of UV-induced changes in frequency shifts. • Frequency shifts are caused by thermal effects and UV conductivity via thin film SAW technology. [ABSTRACT FROM AUTHOR]

A multilayer structure of TeO 2 /interdigital transducers (IDTs)/ZnO ( 1 1 2 ¯ 0 ) /Si(1 0 0) was proposed and investigated to achieve both high sensitivity and temperature-stability for bio-sensing applications. Dispersions of phase velocities, electromechanical coupling coefficients K 2 , temperature coefficient of delay (TCD) and sensitivity in the multilayer structures were simulated as functions of normalized thicknesses of ZnO ( h ZnO / λ ) and TeO 2 (h TeO2 / λ ) films. The fundamental mode of Love mode (LM) - surface acoustic wave (SAW) shows a larger value of K 2 and higher sensitivity compared with those of the first mode. TeO 2 film with a positive TCD not only compensates the temperature effect induced due to the negative TCD of ZnO ( 1 1 2 ¯ 0 ) /Si(1 0 0), but also enhances the sensitivity of the love mode device. The optimal normalized thickness ratios were identified to be h TeO2 / λ = 0.021 and h ZnO / λ = 0.304, and the devices with such structures can which generate a normalized sensitivity of −1.04 × 10 −3 m 3 /kg, a TCD of 0.009 ppm/°C, and a K 2 value of 2.76%. [ABSTRACT FROM AUTHOR]

Transparent microfluidic devices based on ZnO thin film/glass surface acoustic waves (SAWs) were explored for active surface cleaning based on its acoustofluidic performance. Acoustic waves generated from ZnO films on glass substrate were investigated and their acoustofluidic performance including transportation, jetting and nebulization were evaluated. Ash particles and starch solutions were used as model contaminants on the surface of the ZnO/glass SAW devices, and the mass loading of the contaminants on the device's surface was monitored using the SAW device with a high sensitivity of 280.0 ± 9.0 Hz/(μg/mm2). Active surface cleaning of the contaminants was demonstrated based on the transportation of water droplets, and optimized SAW powers were identified which caused strong interactions between water droplet and contaminants, thus effectively cleaning the surfaces. Studies of surface heating effects induced by SAWs showed that the cleaning efficiency was also influenced by the substrate temperature induced by SAW agitations. [Display omitted] • An active surface cleaning platform is developed based on acoustofluidics generated using ZnO/glass thin film acoustic waves. • Monitoring surface contaminants is achieved using the same surface acoustic wave (SAW) device. • Efficiency of active surface cleaning is based on various acoustofluidics functions and acousto-surface heating effect. • Integrated functions with feedback of contamination and active surface cleaning based on SAW device are proposed. [ABSTRACT FROM AUTHOR]

There are significant challenges in controlling uniformity of crystal inclination angles, growth orientations and film thicknesses to generate dual-mode surface acoustic waves (e.g., Rayleigh ones and shear-horizontal ones) for lab-on-a-chip applications. In this study, we demonstrate large area (up to three inches) and uniformly inclined piezoelectric ZnO films, sputtering-deposited on silicon using a glancing angle deposition method. Characterization using X-ray diffraction showed that the inclined ZnO films have an average crystal inclination angle of 29.0°, apart from the vertical (0002) orientation, at a substrate tilting angle of 30o. Reflection signals of ZnO/Si surface acoustic wave devices clearly show the generations of both shear horizontal surface acoustic waves and Rayleigh waves. The Rayleigh waves enable efficient acoustofluidic functions including streaming and transportation of sessile droplets. Excitation direction of Rayleigh waves on the acoustofluidics versus the inclined angle direction has apparent influences on the acoustofluidic performance due to the anisotropic microstructures of the inclined films. The same device has been used to demonstrate biosensing of biotin/streptavidin interactions in a liquid environment using the shear-horizontal surface acoustic waves, to demonstrate its potential for integration into a complete lab-on-a-chip device. [ABSTRACT FROM AUTHOR]

• Numerical and experimental investigations of large deformation of droplet interface actuated by surface acoustic waves (SAWs). • Application of coupled level set volume of fluid (CLSVOF) method to capture deformation of droplet interface induced by SAWs. • Development of a dynamic contact angle model to simulate dynamics of three-phase contact line motion. • Optimisation of electrode configurations for efficient droplet streaming and jetting induced by SAW device. Surface acoustic wave (SAW) based technologies have recently been explored for various sensing and microfluidic applications, and numerous experimental studies and numerical modelling of SAW streaming and liquid-solid interactions have been performed. However, the large deformation of droplet interface actuated by SAWs has not been widely explored, mainly due to the complex physics of SAW-droplet interactions and interfacial phenomena. In this paper, a computational interface tracking method is developed based on the couple level set the volume of fluid (CLSVOF) approach to simulate the interactions between liquid and acoustic waves and deformation of the liquid-air surface. A dynamic contact angle boundary condition is developed and validated by experimental results to simulate the three-phase contact line dynamics. The modified CLSVOF method is then used to study the droplet jetting and internal streaming behaviours by analyzing the energy terms within the liquid medium. Furthermore, by applying the numerical model, effects of configurations and positions of two interdigital transducers (IDTs) on droplet actuation have been investigated to achieve efficient mixing, separation, and jetting. Results show that two perfectly aligned IDTs are optimal for mixing applications. In contrast, two offset IDTs are optimal for concentration and separation applications. The maximum jetting velocity and minimum jetting time are achieved by using a pair of aligned IDTs, whereas by using the two offset IDTs, effective liquid mixing and jetting are observed which can be used in bioprinting applications. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• Real-time detection of CEA using SAW device. • Obtained a limit of detection of 0.31 ng/ml of CEA. • SAW devise for anti-CEA with minimum increase in insertion loss under liquid state analysis. • High selectivity towards CEA from a mixture of similar tumour marking proteins. • High stability over 30 days with only around 8% performance lose. • Validated using Langmuir and Freundlich sorption isotherms. A Love-mode surface acoustic wave (SAW) biosensor based on ST-cut quartz was developed for highly selective and label-free detection of carcinoembryonic antigen (CEA). The delay line area of an interdigital transducer (IDT) based SAW device was coated with gold and then chemically modified through thioglycolic acid–EDC/NHS reaction mechanism. A self-assembled monolayer of anti-CEA was further immobilized on the bioreceptors through the coupling layer. The biosensing capability of the SAW device was evaluated using solutions of CEA with various concentrations and limit of detection was obtained at 0.31 ng/ml of CEA, which is better than the results reported by the literatures available for CEA detection using SAW device. The real-time detection capability of the biosensor was evaluated using clinical serum samples and selectivity was evaluated using mixed solutions of CEA with other common tumor marking proteins. Long-term stability of the biosensor was also evaluated over a period of 30 days and the immunoassay response has shown only 8% decrease in performance within the whole period. The binding of CEA onto the bioreceptor was evaluated through Langmuir and Freundlich sorption isotherm kinetic studies as well. [ABSTRACT FROM AUTHOR]

Herein, presents a novel method for the preparation of a Love mode SAW biosensor for the selective detection of carcinoembryonic antigen (CEA) using a transuding polymer nanocomposite thin film based bioreceptor. Graphene oxide (GO) was synthesized using modified Hummers' method and flower-like MoS 2 nanoparticles were allowed to grow on the 2D layers GO. The rGO-MoS 2 was further used as a host for the synthesis of Au nanoparticles (AuNP) and the final three-component nano-cluster was introduced to the previously synthesized polyamic acid diethyl ethanolamine salt precursor. The uniform mixture was coated on the delay line area of SAW device and conducted thermal imidization process to obtain polyimide nanocomposite. The thickness of the thin film was optimized based on the insertion loss and centre frequency response of the SAW device. Further, anti-CEA self-assembled monolayer (SAM) based bioreceptor was prepared on the polyimide nanocomposite thin film through thioglycolic acid – EDC/NHS immobilization mechanism. The bioreceptor was tested for immunoassay analysis with CEA solution with varying concentrations. The LOD of the biosensor was estimated at 0.084 ng/ml. The real-time applicability of the biosensor was validated using clinical serum sample analysis and the selectivity was evaluated through the affinity test towards other common tumour marking proteins. The biosensor also showed excellent stability, only 10% reduction activity was observed till 80th day of storage. The antigen-antibody adsorption parameters were also evaluated through Langmuir and Freundlich adsorption isotherms. • A novel nanomaterial cluster of AuNP-MoS 2 -rGO was synthesised. • A thin film of the same with PI was used for biosensing of CEA. • Limit of detection of the biosensor was obtained at 0.084 ng/ml. • The biosensor has recorded excellent stability for 70-80 days. • The biosensor was validated through clinical serum sample analysis and compared with ELISA results. [ABSTRACT FROM AUTHOR]

Droplet deformation and force analysis on the inclined surface driven by the SAW. • Acoustofluidics along inclined surfaces have been investigated using AlN/Si Rayleigh surface acoustic waves. • At the inclination angle of 90°, a higher threshold pumping power is needed. • Effects of surface inclination angle on the jetting angle can be neglected for droplets with volume less than 2 μL. • AlN/Si SAWs can be used for both actuators and acoustic heaters to achieve potential lab-on-a-chip applications. Conventional acoustofluidics are restricted to manipulation of droplets on a flat surface, and there is an increasing demand for acoustofluidic devices to be performed at inclined surfaces to facilitate multilayered microfluidic device design and enhance system compactness. This paper reports theoretical and experimental studies of acoustofluidic behaviors (including transportation/pumping and jetting) along inclined surfaces using AlN/Si Rayleigh surface acoustic waves (SAWs). It has been demonstrated that for droplets with volume smaller than 3 μL, they could be efficiently transported on arbitrary inclined surfaces. The gravity effect would play a more and more important role in uphill climbing with the increased inclination angle. When the inclination angle was increased up to 90°, a higher threshold power was needed to transport the droplet and the maximum droplet volume which can be pumped also reached its minimum value. Effects of surface inclination angle on droplet jetting angles could be neglected for their volumes less than 2 μL. Moreover, microfluidic and acoustic heating performances of AlN/Si SAWs were further studied and compared with those conventional ZnO/Si SAWs with the same electrode configurations. [ABSTRACT FROM AUTHOR]