A Novel Surface Acoustic Wave Biosensor for Real-Time Monitoring of Cell Contractile Properties

Abstract

Introduction Contraction of cardiomyocytes is a vital property of the heart and its assessment is significant for drug discovery. At present, many researches focus on the electrophysiology detection through microelectrode arrays (MEAs) [1-2]. However, mechanical properties of cardiomyocytes is also critical for many biological processes including cell growth, motility, division, differentiation, and tissue homeostasis [3]. Currently, the atomic force microscope (AFM) has been used to measure the contractile properties of cardiomyocytes. However, the AFM is only suitable for single cells and can only measure one cell at one time. Therefore, it’s necessary to develop a detection system that can monitor the contractile properties of cardiomyocyte in a real-time and dynamic way.Recently, the surface acoustic wave (SAW) sensor has been greatly developed as a well-performed mass sensing device for label-free immunoassay due to its attractive advantages, including real-time monitoring and simplicity of use [4]. In particular, the guided shear horizontal (SH) SAW sensor, which is also known as the Love Wave sensor, has shown its advantages in biosensor applications due to its high sensitivity and stability in the liquid phase [5]. Hence, SAW is a device capable of monitoring viscoelastic properties of a population of cells, which correlates with stiffness, in a non-invasive, label free and continuous manner up to several days to weeks.In this study, a Love Wave sensor was used to study the contractile properties of HL-1 cardiomyocytes, where changes in insertion loss and phase position of the sensor can reflect the mechanical changes (contraction and viscoelasticity). Different compounds were added to test the different effects on the contractile properties of HL-1 cardiomyocytes, and the signals were analyzed by principal component analysis (PCA). Method In this study, the Love Wave sensor is constructed based on a piezoelectric quartz substrate. Interdigitated transducers (IDTs) with Ti/Au (20/200 nm) are deposited to generate pure shear horizontal acoustic waves. The input and output IDTs electrodes consist of 50 split-finger pairs with a wavelength λ=28 μm, which determines the center frequency of the sensor to be about 160 MHz [4]. The distance between IDTs centers is 200λ and the acoustic aperture is 75λ. Afterwards, the IDTs patterned substrate is guided with a 3 μm SiO2 film deposited by plasma enhanced chemical vapor deposition (PECVD). Au layer (200 nm) is deposited on top of guiding layer to improve the cell attachment on the sensor surface.A polydimethylsiloxane (PDMS) chip was designed and used as the cell culturing chamber. The height and volume of this cavity are about 10 mm and 150 μL, respectively. A portable and miniaturized multi-channel Love Wave sensor detection system was developed to detect both the insertion loss and phase signals of sensors. And then, HL-1 cardiomyocytes with 10,000 cells were seeded on the sensor chip. To test the function of the detection system, isoprenaline (ISO) and verapamil (VRP) with different concentrations were used to induce changes in the contractile properties of HL-1 cells. Results and Conclusions VRP is a calcium channel antagonist that blocks the L-type calcium channel and prevents calcium influx into the cell, thereby decreasing the cardiomyocyte contraction force. With the addition of VRP solutions, the insertion loss of Love Wave sensors increased, and the magnitudes of insertion loss increased with the increase of VRP concentration. Our results indicated that the stiffness of living HL-1 cells decreased after VRP administration. Moreover, the higher the VRP concentration is, the softer the HL-1 cells are within the dosage range tested. In contrast to VRP, ISO is positive inotropic drug. After ISO treatment, HL-1 cells wrinkled due to the traction forces. Therefore, the higher the ISO concentration, the larger the traction force and the tighter is the contact of the cells with the sensor substrate, and the stiffer the cells. Moreover, the responses of SAW sensor treated by VRP and ISO could be distinguished by PCA.As far as we know, this is the first report that study the contractile properties of a cardiomyocytes cell line based on a SAW biosensor. The affection on cardiac contractility of different compounds can be monitored by recording the changes in insertion loss and phase position of the SAW sensor. Our results demonstrated that the SAW sensor is a potential new tool for in vitro cardiac contractility evaluation and has promising applications in drug discovery, safety screening and many other fields.