A review of thermal impact of surface acoustic waves on microlitre droplets in medical applications

The surface acoustic waves (SAW) propagate inside the microdroplets resulting in kinetic and thermal impacts. The kinetic drives fluid particles inside the droplet while thermal impact increases the liquid’s temperature. This paper provides a comprehensive review of the research investigations related to internal kinetics and heating inside the microdroplet caused by the acoustic waves. The main factors that affect the kinetics and convection heat transfer are the piezoelectric materials, shape of the interdigital transducer (IDT) and mode of acoustic waves. Internal streaming (kinetic) leads to particle mixing, particle manipulation, cell sorting, cell patterning, cell separation, measuring the concentration of immunoglobulin and so forth. The effect of changing the mode of waves and the shape of IDT on the relevant applications are presented. Internal convection heat transfer is important where heating of the liquid is essential for many applications such as monitoring blood coagulation in the human plasma and an acoustic tweezer for particle trapping. Experimental methods developed by researchers to realise uniform temperature with constant heating and cooling cycles are also discussed. Such methods are widely used in the polymerase chain reaction (PCR) to detect COVID-19 infection. The heating of the droplet can be efficiently controlled by changing the input power and by varying the duty factor

Experimental investigation of thermal and kinetic impacts of surface acoustic waves on water droplet

An analysis model for investigation of the coupling of kinetic and thermal impacts of surface acoustic wave (SAW) on a microscale droplet is proposed. The model is based on mass, momentum, and energy conservation principles with assistance from experimental observations. The investigation is carried out on a 25 µl water droplet placed on the SAW device fabricated on an aluminium (Al) plate substrate with deposition of 5 µm thick zinc oxide (ZnO) as a top layer. The devices have a thickness of 200 µm and 600 µm with the wavelength (λ) of 100 µm and 200 µm using Rayleigh, Sezawa, and a Lamb and Rayleigh hybridized mode. The SAW input power values are from 0.30 W to 4.0 W with a temperature range of 5-30 °C in this study. A charged-coupled device (CCD) camera has been employed to monitor streaming inside the droplet. To visualise the streaming, 10 µm red polystyrene particles have been used whereas the velocity of particles estimated using particle image velocimetry (PIV). An infrared (IR) thermal camera has been used to detect the droplet surface temperature. However, temperature distributions of fluid layers of the droplet are estimated by developing a MATLAB code. The data has been used in the implementation of the analysis model to interpret the coupling mechanism inside the droplet. The thermal impact includes energy absorbed by the droplet, heat transfer from the substrate to the droplet, from the droplet to the air and the waves penetrated to the droplet (radiation). Whereas kinetic impact involves energy transferred by the streaming and friction inside the droplet. Since this study is based on temperatures much lower than the boiling temperature, no phase change or evaporation observed, therefore, no significant mass transfer has been observed either with Rayleigh or Sezawa. However, at input power (Pin) of 4.0 W using Rayleigh wave (R-wave) where the droplet slightly moves away on the surface in the direction of the waves. Since Sezawa waves (S-waves) travel in the interlayers, they have less SAW force because of which droplet sticks to the surface and does not move away even at higher input power. It has been observed that the thermal impacts of the SAW are more dominant than the kinetic when considering both Rayleigh and Sezawa wave modes. However, the streaming plays a key role in enhancing the heat transfer inside the droplet by internal convection. The major source of thermal impact is the radiation of SAW power (~ 0.05 W to 0.20 W) penetrated to the droplet at input power (Pin) ranging from 0.96 W to 3.2 W, while, at the power of 0.38 W or lower, is from both the SAW radiation (~0.025 W) and hot substrate (~0.01 W) using Rayleigh waves. Inverse heat flux from droplet to the substrate is observed after ‘reverse time’ at Pin > 0.50 W and Pin > 1.0 W for Rayleigh and Sezawa, respectively. Heat always transfers from droplet to the air since this is the heat leaving the system. The thermal impacts of both Rayleigh and Sezawa modes on the droplet showed an exactly similar trend when compared to each other based on the results from the analysis model and experimental data. However, the thermal impacts of SAW on the droplet with a Sezawa wave is slightly less as compared to the Rayleigh. The thermal energy absorbed by the droplet using Rayleigh waves is 4% more as compared to the Sezawa at an input power of 0.96 W. However, this dropped to 1.5% at a higher input power of 3.2 W after the same time frame. It has been found that using the same wave mode, temperature rise inside the droplet is directly proportional to the resonant frequency of the device. Furthermore, Lamb and Rayleigh hybridized waves generate intense thermal impacts, showed 3.5 times and 2.5 times higher temperature as compared to the pure Rayleigh mode at Pin of 2.2 W and 3.2 W, respectively. The same trend and difference have been observed when the hybridized mode is compared with pure Sezawa mode

Theoretical and experimental development of a ZnO-based laterally excited thickness shear mode acoustic wave immunosensor for cancer biomarker detection

The object of this thesis research was to develop and characterize a new type of acoustic biosensor - a ZnO-based laterally excited thickness shear mode (TSM) resonator in a solidly mounted configuration. The first specific aim of the research was to develop the theoretical underpinnings of the acoustic wave propagation in ZnO. Theoretical calculations were carried out by solving the piezoelectrically stiffened Christoffel equation to elucidate the acoustic modes that are excited through lateral excitation of a ZnO stack. A finite element model was developed to confirm the calculations and investigate the electric field orientation and density for various electrode configurations. A proof of concept study was also carried out using a Quartz Crystal Microbalance device to investigate the application of thickness shear mode resonators to cancer biomarker detection in complex media. The results helped to provide a firm foundation for the design of new gravimetric sensors with enhanced capabilities. The second specific aim was to design and fabricate arrays of multiple laterally excited TSM devices and fully characterize their electrical properties. The solidly mounted resonator configuration was developed for the ZnO-based devices through theoretical calculations and experimentation. A functional mirror comprised of W and SiO2 was implemented in development of the TSM resonators. The devices were fabricated and tested for values of interest such as Q, and electromechanical coupling (K2) as well as their ability to operate in liquids. The third specific aim was to investigate the optimal surface chemistry scheme for linking the antibody layer to the ZnO device surface. Crosslinking schemes involving organosilane molecules and a phosphonic acid were compared for immobilizing antibodies to the surface of the ZnO. Results indicate that the thiol-terminated organosilane provides high antibody surface coverage and uniformity and is an excellent candidate for planar ZnO functionalization. The fourth and final specific aim was to investigate the sensitivity of the acoustic immunosensors to potential diagnostic biomarkers. Initial tests were performed in buffer spiked with varying concentrations of the purified target antigen to develop a dose-response curve for the detection of mesothelin-rFc. Subsequent tests were carried out in prostate cancer cell line conditioned medium for the detection of PSA. The results of the experiments establish the operation of the devices in complex media, and indicate that the acoustic sensors are sensitive enough for the detection of biomolecular targets at clinically relevant concentrations.Ph.D.Committee Chair: William D Hunt; Committee Member: Bruno Frazier; Committee Member: Dale Edmondson; Committee Member: Marie Csete; Committee Member: Peter Edmonson; Committee Member: Ruth O'Rega

Acoustic Waves

The concept of acoustic wave is a pervasive one, which emerges in any type of medium, from solids to plasmas, at length and time scales ranging from sub-micrometric layers in microdevices to seismic waves in the Sun's interior. This book presents several aspects of the active research ongoing in this field. Theoretical efforts are leading to a deeper understanding of phenomena, also in complicated environments like the solar surface boundary. Acoustic waves are a flexible probe to investigate the properties of very different systems, from thin inorganic layers to ripening cheese to biological systems. Acoustic waves are also a tool to manipulate matter, from the delicate evaporation of biomolecules to be analysed, to the phase transitions induced by intense shock waves. And a whole class of widespread microdevices, including filters and sensors, is based on the behaviour of acoustic waves propagating in thin layers. The search for better performances is driving to new materials for these devices, and to more refined tools for their analysis

Micro-Resonators: The Quest for Superior Performance

Microelectromechanical resonators are no longer solely a subject of research in university and government labs; they have found a variety of applications at industrial scale, where their market is predicted to grow steadily. Nevertheless, many barriers to enhance their performance and further spread their application remain to be overcome. In this Special Issue, we will focus our attention to some of the persistent challenges of micro-/nano-resonators such as nonlinearity, temperature stability, acceleration sensitivity, limits of quality factor, and failure modes that require a more in-depth understanding of the physics of vibration at small scale. The goal is to seek innovative solutions that take advantage of unique material properties and original designs to push the performance of micro-resonators beyond what is conventionally achievable. Contributions from academia discussing less-known characteristics of micro-resonators and from industry depicting the challenges of large-scale implementation of resonators are encouraged with the hopes of further stimulating the growth of this field, which is rich with fascinating physics and challenging problems

Structural, Magnetic, Dielectric, Electrical, Optical and Thermal Properties of Nanocrystalline Materials: Synthesis, Characterization and Application

This book is a collection of the research articles and review article, published in special issue "Structural, Magnetic, Dielectric, Electrical, Optical and Thermal Properties of Nanocrystalline Materials: Synthesis, Characterization and Application"

21st Century Nanostructured Materials

Nanostructured materials (NMs) are attracting interest as low-dimensional materials in the high-tech era of the 21st century. Recently, nanomaterials have experienced breakthroughs in synthesis and industrial and biomedical applications. This book presents recent achievements related to NMs such as graphene, carbon nanotubes, plasmonic materials, metal nanowires, metal oxides, nanoparticles, metamaterials, nanofibers, and nanocomposites, along with their physical and chemical aspects. Additionally, the book discusses the potential uses of these nanomaterials in photodetectors, transistors, quantum technology, chemical sensors, energy storage, silk fibroin, composites, drug delivery, tissue engineering, and sustainable agriculture and environmental applications

The development and optimisation of a novel microfluidic immunoassay platform for point of care diagnostics

Protein biomarkers are important diagnostic tools for detection of non-communicable diseases, such as cancer and cardiovascular conditions. In order to be used as diagnostic tools they need to be detected at very low concentrations in biological samples (e.g. whole blood, serum or urine). This has been currently performed in central laboratories using expensive, bulky equipment and time consuming assays. [Continues.

SELF-ORGANIZATION IN MICROWAVE FILAMENTARY DISCHARGES

We studied the self organising phenomena im filamntary microwave discharge at various pressures and excitation types