Hongfei Zu

Theoretical analysis of a Love wave biosensor in liquid with a viscoelastic wave guiding layer

The Love mode surface acoustic wave biosensor is considered as one of the most promising probing methods in biomedical research and diagnosis, which has been applied to detect the mechano-biological behaviors of cells attached to the surface of the device. Recent studies have reported the structural and functional optimization of Love wave biosensors for reducing propagation loss and improving sensitivity; however, the relevant device performance needs to be analyzed in depth in terms of device structure, electromechanical properties of piezoelectric crystal substrates, viscoelastic properties of wave guiding layers, and the effect of liquid loading. In this study, a 36° YX-LiTaO3 based Love wave sensor with a parylene-C wave guiding layer is considered as a cell-based biosensor. A theoretical model is proposed to describe the Love wave propagation in the wave guiding layer and penetration in the liquid medium. Decay length δ for the Love wave penetration in liquid is found to be in the order of ∼50 nm, w...

Characterization and temperature sensor application of Ca 3 TaGa 3 Si 2 O 14 crystals

In this paper, the elastic, piezoelectric, and dielectric constants of Ca₃TaGa₃Si₂O₁₄ (CTGS) single crystals were fully characterized from room temperature to 800°C according to IEEE standard methods. The sensitivity and stability of the temperature sensors based on CTGS crystals were also investigated. One of the elastic stiffness constants-c₁₁^E shows the highest temperature sensitivity. The results of the repeated measurements of X-cut square-plate resonator sample indicate its excellent stability through the entire measurement temperature range.

Monitoring the adhesion process of tendon stem cells using shear-horizontal surface acoustic wave sensors

Cell adhesion to a substrate or extracellular matrix (ECM) plays an important role in a variety of cellular functions, such as cell migration, proliferation, differentiation, and tissue formation. Shear-horizontal surface acoustic wave (SH-SAW) sensors can detect cell behaviors in liquid in a non-invasive, simple and quantitative manner. As the key part of SH-SAW, acoustic-wave guiding layer plays a crucial role in improving sensor performance. Parylene-C (poly(2-chloro-p-xylylene)) has been proven as ideal guiding layer due to its good uniformity, compactness and adhesion to substrate. Of comparable cell and protein compatibility to the tissue culture substrate, parylene-C films also have preferable effects as the bio-sensitive interface on SH-SAW sensors. In this study, SH-SAW sensor with parylene-C acoustic-wave guiding layer was adopted to monitor the adhesion process of tendon stem cells (TSCs), a newly discovered stem cell type in tendons. TSC suspensions of different concentrations (0.5×105, 1.0×105, 2.0×105, 4.0×105 cell/ml) were added to collagen-coated PDMS wells successively. The cells were maintained in the incubator for 10 hr, during which corresponding S21 spectrums were recorded every 1 min. The results indicated that there was a sharp increase in S21 loss in the beginning of incubation. With incubation continued, the increase rate reduced gradually, and S21 loss tended to be stable. S21 phase decreased continuously at first, and then entered a plateau with continued incubation. These changes are considered to be related to the integrin-ECM protein interactions and focal adhesion formation occurring in TSC adhesion process. In addition, as TSC suspension concentration increased, the final value of S21 loss change due to TSC adhesion was increased. SH-SAW sensors exhibit high sensitivity and stability in TSC adhesion monitoring, indicating their potential for investigating cell biology in general and cell adhesion in particular.

Properties of piezoelectric single crystals Ca 3 TaGa 3 Si 2 O 14 at high temperature and high vacuum conditions

In this paper, a kind of fully ordered langasite family crystals Ca3TaGa3Si2O14 (CTGS) were grown by the Czochralski pulling method and cut into lateral mode. The dielectric, elastic and piezoelectric properties of them were investigated as functions of temperature (up to 1073.15 K) and pressure (up to E-7 torr). It was found that all the crystals exhibited pressure stability properties and temperature dependent characteristics. According to the calculation, the dielectric permittivity, elastic coefficient and piezoelectric coefficient were about 17.66, 9.06 pm2/N and 3.77 pC/N, respectively. The good properties make CTGS promising candidates for sensing applications at high temperature and high vacuum conditions.

High temperature piezoelectric bulk acoustic wave mass sensor for thermogravimetric analysis of nano-layer polymer

The acoustic wave (AW) sensors can response to a physical, chemical, or biological stimulus in a sensitive and real-time manner, so they have drawn increasing attraction in recent years. Among the AW sensors, the piezoelectric ones show a lot of extraordinary merits such as high resolution, wide frequency and temperature ranges, high stability, low power consumption, and low cost, and they are able to sense many physical and chemical quantities such as temperature, pressure, mass, gas concentration, and liquid viscosity [1-3]. To date, many surface acoustic wave (SAW) sensors [4], thin film bulk acoustic resonators (FBAR) [5], and bulk acoustic wave (BAW) [6] sensors have been reported as mass sensors. Compared to the former two types, BAW mass sensors are with the property of simple preparation process, easy to use, high temperature-tolerance, high repeatability and durability, and little damping, because neither the interdigitated transducers (IDTs) nor the functional piezoelectric thin film is needed. Therefore, piezoelectric BAW mass sensors that can be used at elevated temperature range are ideal devices for thermogravimetric analysis (TGA) applications.

A love wave biosensor with a phononic wave guiding layer for VEGF detection in selective platelet activation

Platelets are blood cells that play a critical role in a number of pathophysiological processes. After activation, platelets release a variety of growth factors, including PDGF, VEGF, TGF-β and HGF. Using different agonists, platelets can be selectively activated in different ways. For example, PAR-1 agonist activated platelets release VEGF while PAR-4 agonist activated platelets retain VEGF in them. Thus, detection of secreted growth factors under the activation of different agonists is essential for the effective clinical use of platelets for optimal injured tissue repair. Love wave sensor is considered as a promising biosensing platform in biomedical research, and more efforts need be devoted to improve the sensor performance. Phononic crystals are periodic composite materials with periodic scattering centers; and acoustic wave in certain frequencies cannot propagate through this kind of frequency band structure. In this study, a Love wave sensor with an innovative phononic wave guiding layer is proposed to detect the VEGF secreted during the selective platelet activation process.

Growth, characterization and piezoelectric applications of langasite-type and YCOB crystals

The research works of thirteen langasite-type crystals and YCOB crystal grown in SICCAS since 2002 were reported. Their piezoelectric properties at room temperature and high temperature up to 900°C were characterized in two cooperation universities and the product applications of SAW sensors and accelerometers in a German company were summarized here.

Characterization of elastic constants of Ca 3 TaGa 3 Si 2 O 14 at high temperatures by Antenna Transmission Acoustic Resonance

In this work, the elastic constants of Ca3TaGa3Si2O14 (CTGS) crystals are characterized in a wide temperature range up to 800°C according to a recently proposed method: Antenna Transmission Acoustic Resonance (ATAR) method. In the ATAR measurement, the electrodes and the wires clamp are not required, which could help to avoid the influences of the mass and force loadings. More importantly, by the ATAR method, all the elastic constants could be obtained through a single frequency sweep of a single randomly cut sample, which makes the measurement time-saving. The system and procedures for the ATAR measurement are presented. And the elastic constants and their temperature dependence are all obtained and compared with the results determined by the IEEE dynamic method.

Label-free detection of protein released during platelet activation by CNT-enhanced love mode SAW sensors

Platelet-rich plasma (PRP) has been applied in a series of clinical treatments. PRP contains high-concentrated platelets, which, when activated, could secret a variety of growth factors and cytokines, to promote and/or enhance healing of injured tissues. Non-activated platelets suspension could be prepared by an isolation method of centrifugation and washing currently. However, it is not clear whether platelets, if any, are already activated during this process and there is no simple method to monitor their activation accordingly. Shear-Horizontal Surface Acoustic Wave sensors (SH-SAW, Love Mode) are promising in fundamental biology as well as biomedical engineering, detecting cell behaviors in liquid in a non-invasive, simple and quantitative manner. In this study, Love mode sensors are adopted for the label-free detection of protein secreted by platelets. Carbon nanotube (CNT) is reported as an advisable platform of both non-specific protein adsorption and specific protein binding. For further improvement of Love mode sensor performance, novel CNT-coated parylene-C film is prepared on its surface as both the acoustic-wave-guiding layer and bio-interface layer. The S21 loss curves of Love mode sensors were recorded and the corresponding resonance frequencies were extracted. The results showed that the CNT-enhanced sensor possessed an increased resonance frequency shift when compared to normal sensor with single parylene-C film under identical collagen concentrations. Then, the modified sensor is used for label-free detection of protein released by various concentrations of platelets. The results revealed high sensitivity and consistency, indicating the potential of CNT-enhanced Love mode sensors in cell-based applications.

Surface acoustic wave mass sensor based on 128° YX-cut Lithium Niobate for thermogravimetric analysis

In this paper, a surface acoustic wave (SAW) mass sensors based on Lithium Niobate (LN) was tested through thermogravimetric analysis (TGA) process up to 450°C. The SAW sensor exhibited good stability and the resonant frequencies decreased linearly with the increase of temperature (the rate was about 5.3 KHz/°C) up to 500°C. PMMA A4 and C9 were deposited as the mass loadings during the TGA process. The mass sensitivity of the sensors was found to be about 13 KHz/μg, which is much higher than the typical QCM microbalance sensors.