Love Wave Sensor Research Articles

Nucleosides analogues recognition by molecularly imprinted polymer‐coated Love wave sensor

Presented is a process for thin film molecularly imprinted polymer (MIP) coating based on commercial nucleotides adenosine monophosphate (AMP). The compatibility of the MIP film with acoustic propagation and sensor sensitivity for rebinding of AMP have been verified. Thin and porous layers of AMP-based MIP layers were successfully deposited on the sensor surface. Detection tests of AMP have been performed in aqueous media. The sensor response was recorded in terms of frequency and total insertion losses after both steps: AMP extraction from MIP then AMP rebinding. The sensor showed high sensitivity to 25 ppm AMP concentration. The effect of the extraction time on rebinding capacity of the MIP layer has been proven.

Comparison of two types of acoustic biosensors to detect immunoreactions: Love-wave sensor working in dynamic mode and QCM working in static mode

A Love-wave device and a PDMS microfluidic chip have been developed in order to measure immunoreactions in liquid media, operating in dynamic mode (continuous flow-through). The obtained results with the above system for the detection of rabbit immunoglobulin by means of an antibody of goat anti-rabbit have been compared with those obtained by the most used acoustic wave device, the quartz crystal microbalance (QCM), which has worked in static mode. It has been demonstrated once again that QCM is an excellent tool as an immunosensor, although the Love-wave device is a good alternative due to its higher sensitivity.The dynamic mode improves the response time and the limit of detection. In addition, the use of microchannels has allowed working with a small sample volume for a long period of time in dynamic mode.On the other hand, a secondary antibody conjugated with gold nanoparticles has been used as a different method to measure the desired concentrations of antigens, obtaining in this case, a greater frequency shift.

Temperature Compensation Experiment of Love Wave Sensor

Love wave sensor is one of the most promising SAW sensors for liquid detection, because of acoustic energy can be confined in sensing surface by waveguide layer of Love wave sensor, which resulted in higher sensitivity to surface perturbations. Temperature coefficient of frequency (TCF) has deep effect on effective sensitivity of Love wave sensor. In order to improve the performance of Love wave sensor, the theoretical relationship of TCF on substrates and guiding layers temperature properties is researched. It found that reasonable combinations of substrates and guiding layers was a feasible method to obtain effective temperature compensation, and experimental TCF of sensitive element is reduced to 0.75ppm/°C by this method.

Love-wave sensor array to detect, discriminate and classify chemical warfare agent simulants

An array made up of Love wave sensors based on quartz/SiO 2 is proposed as a detection system for chemical warfare agents (CWA). The array is composed of one reference and six devices coated with different polymers means of spray coating technique. The system has been tested with well-known CWA simulants: dimethylmethyl phosphonate (DMMP), dipropyleneglycol methyl ether (DPGME), dimethylmethyl acetamide (DMA), dichloroethane (DCE), dichloromethane (DCM), and dichloropentane (DCP), detecting very low concentrations, such as 40 ppb of DMMP, a simulant of sarin nerve gas. Additionally, principal component analysis (PCA) as a data pre-processing and discrimination technique, and probabilistic neural networks (PNN) as a pattern classification technique, have been applied, obtaining a clear discrimination and a correct classification.

Acoustic sensors as a biophysical tool for probing cell attachment and cell/surface interactions.

Acoustic biosensors offer the possibility to analyse cell attachment and spreading. This is due to the offered speed of detection, the real-time non-invasive approach and their high sensitivity not only to mass coupling, but also to viscoelastic changes occurring close to the sensor surface. Quartz crystal microbalance (QCM) and surface acoustic wave (Love-wave) systems have been used to monitor the adhesion of animal cells to various surfaces and record the behaviour of cell layers under various conditions. The sensors detect cells mostly via their sensitivity in viscoelasticity and mechanical properties. Particularly, the QCM sensor detects cytoskeletal rearrangements caused by specific drugs affecting either actin microfilaments or microtubules. The Love-wave sensor directly measures cell/substrate bonds via acoustic damping and provides 2D kinetic and affinity parameters. Other studies have applied the QCM sensor as a diagnostic tool for leukaemia and, potentially, for chemotherapeutic agents. Acoustic sensors have also been used in the evaluation of the cytocompatibility of artificial surfaces and, in general, they have the potential to become powerful tools for even more diverse cellular analysis.

Increased Sensitivity of Love Wave Delay-Lines for Heavy Metal Detection through the Deposition of a Mesoporous TiO2 Coating

This work deals with the design of a highly sensitive biosensor for heavy metal detection in liquid medium. The developed biosensor consists in an acoustic Love wave sensor with polyelectrolyte multilayers (PEM) and E.coli bacteria as bioreceptors. The PEM represent a versatile polymeric matrix, deposited with an efficient "layer-by-layer" method. Bacteria are immobilized on the PEM, and are used to detect the presence of cadmium because of the modification of their viscoelastic properties induced by heavy metals. The PEM and bacteria deposition, as well as the detection of cadmium are measured through the real-time resonant frequency shifts of the sensor. The impact of the addition of a mesoporous TiO2 layer between the Love wave guiding layer and the PEM has been studied. The subsequent results are compared to those obtained with a "classic" Love wave device (Quartz + SiO2) and highlight an increased sensitivity of the acoustic platform towards cadmium.

Determination of the Physical Properties of Room Temperature Ionic Liquids Using a Love Wave Device

In this work, we have shown that a 100 MHz Love wave device can be used to determine whether room temperature ionic liquids (RTILs) are Newtonian fluids and have developed a technique that allows the determination of the density-viscosity product, ρη, of a Newtonian RTIL. In addition, a test for a Newtonian response was established by relating the phase change to insertion loss change. Five concentrations of a water-miscible RTIL and seven pure RTILs were measured. The changes in phase and insertion loss were found to vary linearly with the square root of the density-viscosity product for values up to (ρη)(1/2) ~ 10 kg m(-2) s(-1/2). The square root of the density-viscosity product was deduced from the changes in either phase or insertion loss using glycerol as a calibration liquid. In both cases, the deduced values of ρη agree well with those measured using viscosity and density meters. Miniaturization of the device, beyond that achievable with the lower-frequency quartz crystal microbalance approach, to measure smaller volumes is possible. The ability to fabricate Love wave and other surface acoustic wave sensors using planar metallization technologies gives potential for future integration into lab-on-a-chip analytical systems for characterizing ionic liquids.

Array of Love-wave sensors based on quartz/Novolac to detect CWA simulants

An array of Love-wave sensors based on quartz and Novolac has been developed to detect chemical warfare agents (CWAs). These weapons are a risk for human health due to their efficiency and high lethality; therefore an early and clear detection is of enormous importance for the people safety. Love-wave devices realized on quartz as piezoelectric substrate and Novolac as guiding layer have been used to make up an array of six sensors, which have been coated with specific polymers by spin coating. The CWAs are very dangerous and for safety reasons their well known simulants have been used: dimethylmethyl phosphonate (DMMP), dipropyleneglycol methyl ether (DPGME), dimethylmethyl acetamide (DMA), dichloroethane (DCE), dichloromethane (DCM) and dichloropentane (DCP). The array has been exposed to these CWA simulants detecting very low concentrations, such as 25ppb of DMMP, a simulant of nerve agent sarin. Finally, principal component analysis (PCA) as data pre-processing and discrimination technique, and probabilistic neural networks (PNN) as patterns classification technique have been applied. The performance of the sensor array has shown stability, accuracy, high sensitivity and good selectivity to these simulants.

Love wave hydrogen sensors based on ZnO nanorod film/36°YX-LiTaO 3 substrate structures operated at room temperature

Love wave hydrogen sensors based on ZnO nanorod layers deposited on 36°YX-LiTaO 3 substrates have been studied. The ZnO nanorod layers are prepared by two steps: first, the seed layers, as well the guiding layers of the Love wave devices, are deposited by RF magnetron sputtering; second, the nanostructural layers, as well the sensing layers of the sensors, are grown by hydrothermal synthesis. Two kinds of ZnO layers have been analyzed by XRD, SEM and XPS. The XRD shows that both ZnO layers have (0 0 2) oriented wurtzite structures. The SEM results reveal that the morphologies of the deposited ZnO seed layers are continuous and compact, while the hydrothermal treated layers are with nanorods almost perpendicular to the substrate surfaces. Finally, the hydrogen sensing responses of the Love wave sensors activated by Pt catalysts are measured for various concentrations of hydrogen in synthetic air at room temperature. The results show that the sensors have high sensitivity and repeatability as the nanorod layers are optimized, such as the frequency shift 8 kHz toward 0.04% of H 2 in synthetic air is obtained while the height of the nanorod layer is about 2.1 μm and the central frequency of the sensor is about 125.5 MHz. The XPS analyses of the sensitive layers show that there are oxygen vacancies in the layers, so the oxygen vacancy model is used to explain the hydrogen sensing mechanism of the Love wave sensors.

Integrated active mixing and biosensing using low frequency vibrating mixer and Love-wave sensor for real time detection of antibody binding event

The development of lab-on-chip devices is expected to dramatically change biochemical analyses, allowing for a notable increase of processing quality and throughput, provided the induced chemical reactions are well controlled. In this work, we investigate the impact of local acoustic mixing to promote or accelerate such biochemical reactions, such as antibody grafting on activated surfaces. During microarray building, the spotting mode leads to low efficiency in the ligand grafting and heterogeneities which limits its performances. To improve the transfer rate, we induce a hydrodynamic flow in the spotted droplet to disrupt the steady state during antibody grafting. To prove that acoustic mixing increases the antibody transfer rate to the biochip surface, we have used a Love-wave sensor allowing for real-time monitoring of the biological reaction for different operating conditions (with or without mixing). An analysis of the impact of the proposed mixing on grafting kinetics is proposed and finally checked in the case of antibody-antigen combination.

Love Wave Bacterial Biosensors and Microfluidic Network for Detection of Heavy Metal Toxicity

The presented work deals with the development of a bacteria-based Love wave sensor platform for the detection of heavy metals in liquid medium. The acoustic delay-line was inserted in an oscillation loop and associated with a Polydimethylsiloxane (PDMS) microfluidic network fabricated using soft photolithography and molding. It resulted in a small platform convenient for fast analysis and detection. Whole bacteria (Escherichia. coli) were fixed as bioreceptors onto the acoustic path of the sensor coated with a polyelectrolyte multilayer (PEM) using a simple and efficient layer by layer electrostatic self-assembly procedure. PEM and bacteria deposition were real-time characterized by monitoring the resonance frequency modification due to mass loading effect. Then when a solution of metal ion (Cd2+, Hg2+) was pumped through the microchannels, a significative frequency variation was observed down to 10-12 mol.l-1 concentration, due to changes of bacteria visco-elastic equivalent parameters in presence of toxic heavy metals.

Love波传感器的性能分析与实验

In order to obtain a high sensitive Love wave mass sensor,the Love wave propagation characteristics in a layered structure consisting of a ST-quartz and a silica were investigated theoretically and experimentally on the basis of acoustic dynamics,the wave equation for the layered structure was analyzed and its displacement and the dispersion curves were obtained by calculation.According to the computing results,a Love wave sensor with a SiO2 waveguide layer was designed and fabricated on a ST-quartz substrate by MEMS processes and its sensitivity was tested by electro-deposition experiment.The results indicate that the mass sensitivity of the device is 100 cm2/g and the detection limit is 3.65 ng,which meets the demand of biochemical detection for higher sensitivity basically.

Discrimination and classification of chemical warfare agent simulants using a Love-wave sensor array

An array made up of Love-wave sensors has been developed as a detection system for chemical warfare agents (CWAs). This array has been tested with well-known CWA simulants detecting very low concentrations, such as 40 ppb of DMMP, a simulant of sarin nerve gas, 250 ppb of DPGME, a simulant of nitrogen mustard and 15ppm of DMA, a simulant of distilled mustard. Additionally, principal component analysis (PCA) as a data pre-processing and discrimination technique, and probabilistic neural networks (PNN) as a patterns classification technique, have been applied, obtaining good results concerning to discrimination and sensitivity.

Quantification of the effect of glycocalyx condition on membrane receptor interactions using an acoustic wave sensor

The effect of the cell glycocalyx on the binding of a membrane receptor, classI major histocompatibility complex (MHC) human leukocyte antigen (HLA)-A2, to an immobilized anti-HLA antibody was investigated using an acoustic sensor based on a Love wave geometry. The enzyme neuraminidase was used to remove sialic acid residues from the cell glycocalyx. Real-time measurements of the amplitude of the acoustic wave showed that treatment with neuraminidase facilitates HLA/anti-HLA-mediated cell attachment via a 3.6-fold increase of the two-dimensional (2D) binding constant of the interaction. This could be attributed to better approach of binding partners due to favorable condition of the desialylated glycocalyx. The results underline the importance of microtopological factors in membrane receptor binding and reveal the potential of the Love wave sensor and 2D binding parameters for studying cell-substrate binding events.

Analysis of viscosity sensitivity for liquid property detection applications based on SAW sensors

An investigation of viscosity sensitivity for liquid property detection applications based on the ZnO/SiO 2/Si layered structure Love mode surface acoustic wave (SAW) sensors is presented. One of our interests in this paper is to optimize the SAW viscosity sensor under the condition of temperature stability by considering the relations among electromechanical coupling coefficient, viscosity sensitivity and temperature coefficient of delay (TCD). Some important results have been obtained by solving the system of coupled electromechanical field equations and Navier–Stokes equation. It is found that the electromechanical coupling coefficient and viscosity sensitivity can be further improved by adjusting the thickness of SiO 2 thin film and a zero TCD device also can be obtained by introducing a SiO 2 thin film with proper thickness. We try to obtain a device which possesses the viscosity sensitivity as high as possible and has zero TCD. Another interest of this paper is to improve the traditional viscosity sensitivity expression by considering the coupling effect between the liquid viscosity and density. It is shown that the coupling effect cannot be neglected from the numerical results. This modification could make the obtained viscosity more accurate. This analysis is meaningful for the manufactures and applications of the ZnO/SiO 2/Si structure Love wave sensor for liquid property detection.

An application of Love SH waves for the viscosity measurement of triglycerides at high pressures

A new ultrasonic method of viscosity measurements at a high-pressure conditions has been presented. The method is based on the Love wave amplitude measurement. The same electronic setup as in the Bleustein–Gulyaev (B–G) wave method applied by the authors recently for a high-pressure measurement was adopted. The new sensors were made of metallic materials, which make them more reliable at high-pressure conditions. The method has been successfully applied for the viscosity measurement of some triglycerides at high-pressure conditions up to 1 GPa. The results have been compared with the earlier results obtained using B–G waves. This comparison has shown that Love wave method sensors are more reliable than B–G wave sensors and are also cheaper in fabrication, although the sensitivity of Love wave sensors is lower. During the measurement, the phase transitions in the investigated liquids were observed.

Fabrication and packaging technologies of Love-wave-based microbalance for fluid analysis

Sensors able to operate with liquid phases are the key-point for the development of biochemical lab-on-chip devices. In this work, we present the design and manufacture of Love-wave sensors equipped with a liquid cell, at the wafer scale level, to allow operation with liquid media. Love-wave sensors are fabricated on AT-cut quartz plates (IEEE Std-176 notation (YXlt)/36/90) and passivated by a 2.5 μ m thick silica overlay. The fabrication process using the celebrated SU-8 epoxy-based photoresist combined with silicon or quartz machined covers is presented, revealing robust enough for ensuring a reproducible sensor fabrication and packaging. Results are reported emphasizing the efficiency of the proposed approach.

Vacuum-deposited wave-guiding layers on STW resonators based on LiTaO 3 substrate as love wave sensors for chemical and biochemical sensing in liquids

A promising approach to apply the Love wave concept to commercially available low-loss surface acoustic wave (SAW) devices of the type Murata SAF 380 is presented. Thin wave-guiding layers of variable thickness are coated on the piezoelectric substrate of the devices. Two different layer materials were used: sputtered SiO 2 and a new polymer in this field, parylene C (poly-[2-chloro-p-xylylene]). Insertion loss, resonance frequency, frequency changes during protein precipitation and noise of the devices are discussed as a function of the thickness of the wave-guiding layer. It is demonstrated that the application of an optimized wave-guiding layer increases the sensitivity. When using SiO 2 as wave-guiding layer, an optimum layer thickness of 4 μm leads to a detection limit of 1.7 pg/mm 2. Therefore, the detection limit is improved by factor 7.7 as compared to uncoated SAW devices. Parylene-coated devices reach a detection limit of 2.9 pg/mm 2 at an optimum layer thickness of 0.5 μm. This corresponds to an improvement by factor 4.3. As the SAW devices used in this study are commercially available at low costs, applying appropriate wave-guiding layers permits an application as chemical or biochemical sensors with excellent sensitivities. Moreover, parylene-coated devices combine the sensitivity increase by excitation of Love waves with an excellent protective effect against corrosive attacks by the surrounding medium. Therefore, these sensors are most suitable for biosensing in conducting buffer solutions.

Probing the interaction of a membrane receptor with a surface-attached ligand using whole cells on acoustic biosensors

Two different types of acoustic sensors, a surface acoustic wave device supporting a Love-wave (Love-SAW) and a quartz crystal microbalance system with dissipation (QCM-D), were used to demonstrate the potential of acoustic devices to probe the binding of a cell membrane receptor to an immobilized ligand. The class I Major Histocompatibility Complex molecule HLA-A2 on the surface of whole cells and anti-HLA monoclonal antibodies immobilized on the sensor were used as an interaction pair. Acoustic measurements consisted of recording the energy and velocity or frequency of the acoustic wave. Results showed that both devices could detect the number of cells in solution as well as the cells bound to the surface. In addition, the Love-wave sensor, which can sense binding events within the relatively short distance of ∼50nm from the device surface, was sensitive to the number of bonds formed between the cell membrane and the device surface while the QCM-D, which can sense deeper within the liquid, was found to respond well to stimuli that affected the cell membrane rigidity (cytochalasin D treatment). The above results suggest that acoustic biosensors can be a powerful tool in the study of cell/substrate interactions and acoustic devices of different type can be used in a complementary way.

Molecular weight influence study of aqueous poly(ethylene glycol) solutions with a microfluidic Love wave sensor

Love wave acoustic sensors have shown through the years a great potentiality regarding measurements in liquid environments, especially in the field of biosensors. Their high sensitivity to surface perturbations make them also good candidates for micro-rheology. In this paper, we demonstrate that a Love wave sensor response is also very sensitive to the molecular structure of polymers by investigating its behavior to aqueous poly(ethylene glycol) solutions of various molecular weights. We also report the ability of this type of sensor to determine the critical molecular weight between entanglements ( M c ) .