ATR-FTIR Spectroscopic Analysis of Sorption of Aqueous Analytes into Polymer Coatings Used with Guided SH-SAW Sensors

Attenuated total internal reflectance Fourier transform infrared (ATR-FTIR) spectroscopy was used for the investigation of sorption of aqueous solutions of analytes into polymer coatings. A series of simple model polymers, such as poly(dimethylsiloxane), poly(epichlorhydrin), and poly(isobutylene), and films and analytes, such as aqueous solutions of ethylbenzene, xylenes, toluene, and nitrobenzene, were used to evaluate the use of ATR-FTIR spectroscopy as a screening tool for sensor development. The ratios of integrated infrared absorption bands provided a simple and efficient method for predicting trends in partition coefficients. Responses of polymer-coated guided shear horizontal surface acoustic wave (SH-SAW) sensor platforms to the series of analytes, using polymer coatings with similar viscoelastic properties, were consistent with ATR-FTIR predictions. Guided SH-SAW sensor responses were linear in all cases with respect to analyte concentration in the tested range. Comparison of ATR-FTIR data with guided SH-SAW sensor data identifies cases where mass loading is not the dominant contribution to the response of the acoustic wave sensor. ATR-FTIR spectra of nitrobenzene, coupled with computational chemistry, provided additional insight into analyte/polymer interactions

Giant spin-vorticity coupling excited by shear-horizontal surface acoustic waves

A non-magnetic layer can inject spin-polarized currents into an adjacent ferromagnetic layer via spin vorticity coupling (SVC), inducing spin wave resonance (SWR). In this work, we present the theoretical model of SWR generated by shear-horizontal surface acoustic wave (SH-SAW) via SVC, which contains distinct vorticities from well-studied Rayleigh SAW. Both Rayleigh- and SH-SAW delay lines have been designed and fabricated with a Ni81Fe19/Cu bilayer integrated on ST-cut quartz. Given the same wavelength, the measured power absorption of SH-SAW is four orders of magnitudes higher than that of the Rayleigh SAW. In addition, a high-order frequency dependence of the SWR is observed in the SH-SAW, indicating SVC can be strong enough to compare with magnetoelastic coupling

Analysis of the Detection of Organophosphate Pesticides in Aqueous Solutions Using Hydrogen-Bond Acidic Coating on SH-SAW Devices

The work presented in this paper focuses on the synthesis and characterization of a hybrid organic/inorganic chemically sensitive layer for rapid detection and analysis of OPs in aqueous solutions using SH-SAW devices. Coated SH-SAW devices on 36° YX-LiTaO and 42.75° YX-Quartz (ST-90° X Quartz), are used to determine the optimum operating conditions for achieving rapid sensor responses with high sensitivity. Three analytes (parathion-methyl, parathion, and paraoxon), having similar molecular mass and volume, are used to evaluate the performance of the hybrid organic/inorganic coating in terms of sensor properties of interest including sensitivity, selectivity, reproducibility. It is shown that the coating has a high degree of partial selectivity and sensitivity towards the analytes. With the present non-optimized chemical sensor, a limit of detection of 60 (ppb), 20 (ppb) and 100 (ppb) is estimated for parathion-methyl, parathion, and paraoxon, respectively, when using a 0.5 -thick BPA-HMTS sensing layer. Concentrations as low as 500 (ppb) parathion have been measured. This concentration is significantly much lower than the typical concentrations found on agricultural produce (≥10 ppm)

Shear-horizontal surface acoustic wave microfluidics for lab-on-chip applications

Surface acoustic wave (SAW) devices based on the piezoelectric principle have been used extensively in telecommunication applications over the last 20 years, but have recently shown promise in the area of biomedical applications due to their efficient micro-fluidic functions and highly sensitive and label-free detection of pathogens, bacteria, cells, DNA and proteins. There are two types of surface acoustic wave modes: i.e., Rayleigh SAW (R-SAW) and shear horizontal SAW (SH-SAW). R-SAW is widely used for microfluidics and sensing in dry conditions, whereas SH-SAW is mainly used for sensing in liquid conditions. This thesis firstly reviewed the current theoretical and research progress related to these devices and application within the biomedical fields to date, and then the SH-SAW was applied into a novel lab-on-chip combining both bio-sensing and micro-fluidic functions. Simulations of the SH-SAW propagation on 36o Y-cut LiTaO3 were undertaken. Results showed a weak vertical wave component, and at a 90° rotation cut, the crystal was able to support a vertical Rayleigh component showing mixed sensing and streaming possibilities on a single crystal. Experimental investigation of the SH-SAW identified the ability for the shear wave to support mixing, pumping, heating, nebulisation and ejection of sessile droplets on the surface of the crystal with a theoretical explanation for the behaviour presented. A comparison with a standard R-SAW devices made of 128o Y-cut LiNbO3 and sputtered ZnO films was performed. This novel behaviour of digital microfludics, i.e., using sessile droplet with the SH-SAW, demonstrated by this work offers the possibility to manufacture a fully integrated micro-fluidic bio-sensing platform using a single crystal to realise a range of micro-fluidic functions

Analysis of Red Blood Cell Samples using a Handheld Shear-horizontal Surface Acoustic Wave Biosensor

Human red blood cells (RBCs) are highly studied by researchers and clinicians alike because RBCs play an essential role in medical diagnostics. RBCs are the most abundant component of whole blood. The accurate analysis of blood samples for blood cells is crucial to help diagnose and management of several life-threatening diseases. Current techniques for analyzing blood cell counts are time-consuming and expensive, requiring a highly trained technician. Implementing a portable, label-free method enables analysis at small clinics and remote locations with reduced times of analysis and cost. The development of miniature, handheld shear-horizontal surface acoustic wave (SH-SAW) biosensors capable of accurately counting RBCs in liquid samples will improve medical diagnostics in resource-limited regions of the United States and parts of the world where access to centralized clinical laboratories is limited. A shear-horizontal surface acoustic wave is a horizontally polarized surface acoustic wave that is produced by a transducer that is fabricated onto a piezoelectric substrate such as lithium tantalate, lithium niobite, or quartz. We report a lithium tantalate SH-SAW biosensor and method for monitoring the RBC level (hematocrit level) from a whole blood sample using a shear-horizontal surface acoustic wave (SH-SAW) biosensor that uses a 500-picoliter sample well. Samples were introduced by directly pipetting whole blood onto the sample reservoir and washing away any excess material. The SH-SAW biosensor uses an immunoassay, where the antibody anti-glycophorin A is coated on the surface of the active area of the sensor. The sample is compared to a reference sample. Using Microsoft Excel statistical tools, we showed that the results demonstrate the concentration dependence of the samples with an average coefficient of variance (CV) within a sample group was 10% or less for all samples analyzed. Our successful demonstration offers proof of concept for handheld blood cell monitors for remote and resource-limited applications. To our knowledge, this is the first demonstration of an SH-SAW device being used for monitoring red blood cell counts

Applications of Acoustic Wave Devices for Sensing in Liquid Environments

Acoustic wave devices such as thickness shear mode (TSM) resonators and shear horizontal surface acoustic wave (SH-SAW) devices can be utilized for characterizing physical properties of liquids and for chemical sensor applications. Basic device configurations are reviewed and the relationships between experimental observables (frequency shifts and attenuation) and physical properties of liquids are presented. Examples of physical property (density and viscosity) determination and also of chemical sensing are presented for a variety of liquid phase applications. Applications of TSMs and polymer-coated guided SH-SAWs for chemical sensing and uncoated SH-SAWs for “electronic tongue” applications are also discussed

Chemically Sensitive Polymer Coatings For SH-Surface Acoustic Wave Sensors for the Detection of Benzene in Water

Polymer-coated shear horizontal surface acoustic wave (SH-SAW) sensors are investigated for the detection of benzene in aqueous samples. The SH-SAW sensors using three-layer geometry have a single polymer sensing layer which absorbs the analyte and interacts with the surface wave. Several polymers are identified as potential improvements over current sensing films based on glass transition temperature and Hildebrand solubility parameter. The polymers investigated in this work include poly (methyl acrylate) (PMA), poly (butyl acrylate) (PBA), poly (ethylene co-vinyl acetate) (PEVA), bisphenol-A poly (dimethylsiloxane) (BPA PDMS), and bisphenol-A poly (hexamethyltrisiloxane) (BPA HMTS). The polymers are spin coated on a lithium tantalate (LiTaO3) SH-SAW dual delay-line device at thicknesses between 0.3 µm and 1.0 µm. Each film\u27s thickness is measured and the film is exposed to multiple concentrations of the aromatic hydrocarbons benzene, ethylbenzene, toluene, and xylenes (BTEX). The added mass and viscoelastic changes in the sensing layer result in a change in center frequency and acoustic loss of the device. The frequency change is measured and used to determine sensitivity of the coated sensor to each analyte. BPA PDMS and BPA HMTS show larger sensitivities to each of the BTEX analytes than PBA, PMA, or PEVA. However, both BPA PDMS and BPA HMTS were observed to lose sensitivity during the aging process. It is shown that the aging effect on BPA HMTS can be mitigated by baking the film after it is applied to the device

SENSORS: Detecting Microbial Pathogens with Novel Surface Acoustic Wave Devices in Liquid Environments

This SENSORS proposal integrates research and education to exploit the sensitivity of a new family of LGX crystal devices operated in novel Shear Horizontal Surface Acoustic Wave (SH-SAW) propagation directions by combining them with highly selective molecular padlock probes to detect specific nucleic acid sequences associated with bacteria such as Escherichia coli O157:H7, Salmonella typhi, and Vibrio cholerae in aqueous solutions. The anticipated fundamental advances in sensor science and engineering will be relevant to numerous applications, including rapid response to bioterrorism, healthcare, epidemiology, agriculture, food safety, and pollution avoidance and mitigation. This SENSORS program builds upon the initial proof-of-concept results provided by an NSF SGER project funded by the divisions of Electrical and Communication Systems, and Bioengineering and Environmental Systems. The intellectual merit of this proposal rests in the creative, integrated research and education activities related to combining the recently identified LGX SH-SAW devices with molecular padlock probe technology to permit the design, fabrication, testing, and optimization of prototype biosensors. The specific research objectives of this SENSORS program are to: (i) Identify the surface density chemistry for increased sensitivity; (ii) Investigate and identify the optimal LGX SH-SAW orientation and device design for operation with the padlock technology; (iii) Study and develop the molecular padlock probe system to operate effectively in conjunction with the LGX SH-SAW device; (iv) Fabricate and test the prototype SH-SAW liquid biosensors; (v) Identify and optimize a procedure for sensor regeneration; and (vi) Characterize and optimize the sensor\u27s dynamic range and cross-effects due to temperature and other physical and chemical factors. The educational objective of this SENSORS program is to provide a multidisciplinary learning experience to students ranging from high school to graduate student level in the area of sensors in general, and biosensors in particular. Broader impacts will be achieved through the following programs and activities to: (i) Train and interact with high school audiences through two major ongoing programs at University of Maine (UMaine), NSF Research Experiences for Teachers (RET) and the GK-12 Sensors; (ii) Involve undergraduates from Maine and other institutions directly into the research project under the umbrella of the ongoing NSF Research Experience for Undergraduates (REU) program at the UMaine; (iii) Expand existing undergraduate Sensor Technology and Instrumentation and Biochemical Engineering Engineering courses at the UMaine by adding modules relating to biosensors devices and systems; (iv) Identify appropriate Capstone projects for undergraduates involving cross-disciplinary research and design projects; (v) Enhance existing graduate level courses Microscale Bioengineering and Design and Fabrication of Acoustic Wave Devices by incorporating research results into the course; (vi) Contribute to the new interdisciplinary multi-institutional NSF Integrative Graduate Education and Research Traineeship (IGERT) program in functional genomics, which involves UMaine, the Jackson Laboratory, and the Maine Medical Center Research Institute; (vi) Provide a experimental and/or theoretical thesis topics for Masters and Ph.D. students; (vii) Disseminate the research and educational material on a project website, and through conferences and printed literature. The SENSORS project proposed here is designed to result in tangible research and educational benefits. It will provide a knowledge base critical to creation of the next generation of biosensors for single unit production and future integration into arrays. It also seeks to establish a model program whereby cross-disciplinary education is integrated with a state-of-the-art research program, providing a rich learning experience for students ranging from high school to graduate student level. Finally, the project will help to strengthen U.S. research and educational capabilities in an area of high technology that currently is in need of highly trained industry and academic professionals

High frequency acousto-electric microsensors for liquid analysis

Liquid sensors are required for a multitude of applications in the food and beverage sectors, in the pharmaceutical industry or environmental monitoring. The focus of this work is on the development of high frequency shear horizontal surface acoustic wave (SH-SAW) sensors for liquid media identification and characterisation. Among the various types of surface acoustic wave modes propagating in solids, the SH-SAWs were found to be the most suitable for operation in liquids. Dual delay line and resonator sensor configurations were designed and fabricated on lithium tantalate (LiTa03) substrates; the design and the subsequent fabrication procedures of the sensors are described in detail. Furthermore, the electrical characterization of the sensors was carried out with a network analyser, and a comparative analysis was performed between sensors with different configurations. The interdigital transducers, used as the interface between the electrical and acoustic domains, presented good reflection coefficients and had near perfect matched impedances and return loss figures up to 45 dB. The insertion loss of the sensors varied with the surface conditions while it was improved by using total or partial metallization of the surface or employing grating structures on the propagation path. The SH-SAW devices were exposed to basic taste solutions and all the sensor configurations tested were able to discriminate them well. Measurements were done in both standard wired set-ups and a semi-wireless set-up, thus proving the sensor's capability for remote operation. Further investigations regarding the electronic tongue applicability of the SH-SAW sensors were conducted on a two port resonator device. The resonator was tested with six basic taste solutions, with taste solutions with varying concentrations, with binary mixtures of taste solutions and proved successful in identifying all test samples. A multivariate analysis was performed on the resonator data, and confirmed that the sensor's responses are influenced by the physical properties of the tested solutions. The multiple linear models derived are statistically significant and can explain high percentage of the data variability, offering a simplified alternative to the complex analytical models of the SH-SAW sensors. Also, a voltage modulated sensor system was proposed for smart assaying of biomaterials and its operation principle is described. The preliminary tests carried out showed a significant voltage effect on carbon nanoparticles. The voltage modulated system is proposed as an analytical microsystem for the screening of bacterial cells. All sensors in this project had no bio-chemical selective layer making them nonspecific, yet they create robust, durable and low-cost systems

Online Drift Compensation for Chemical Sensors Using Estimation Theory

Sensor drift from slowly changing environmental conditions and other instabilities can greatly degrade a chemical sensor\u27s performance, resulting in poor identification and analyte quantification. In the present work, estimation theory (i.e., various forms of the Kalman filter) is used for online compensation of baseline drift in the response of chemical sensors. Two different cases, which depend on the knowledge of the characteristics of the sensor system, are studied. First, an unknown input is considered, which represents the practical case of analyte detection and quantification. Then, the more general case, in which the sensor parameters and the input are both unknown, is studied. The techniques are applied to simulated sensor data, for which the true baseline and response are known, and to actual liquid-phase SH-SAW sensor data measured during the detection of organophosphates. It is shown that the technique is capable of estimating the baseline signal and recovering the true sensor signal due only to the presence of the analyte. This is true even when the baseline drift changes rate or direction during the detection process or when the analyte is not completely flushed from the system