Anis Nurashikin Nordin

Acoustic wave based MEMS devices for biosensing applications

This paper presents a review of acoustic-wave based MEMS devices that offer a promising technology platform for the development of sensitive, portable, real-time biosensors. MEMS fabrication of acoustic wave based biosensors enables device miniaturization, power consumption reduction and integration with electronic circuits. For biological applications, the biosensors are integrated in a microfluidic system and the sensing area is coated with a biospecific layer. When a bioanalyte interacts with the sensing layer, mass and viscosity variations of the biospecific layer can be detected by monitoring changes in the acoustic wave properties such as velocity, attenuation, resonant frequency and delay time. Few types of acoustic wave devices could be integrated in microfluidic systems without significant degradation of the quality factor. The acoustic wave based MEMS devices reported in the literature as biosensors and presented in this review are film bulk acoustic wave resonators (FBAR), surface acoustic waves (SAW) resonators and SAW delay lines. Different approaches to the realization of FBARs, SAW resonators and SAW delay lines for various biochemical applications are presented. Methods of integration of the acoustic wave MEMS devices in the microfluidic systems and functionalization strategies will be also discussed.

A novel cell-based hybrid acoustic wave biosensor with impedimetric sensing capabilities

A novel multiparametric biosensor system based on living cells will be presented. The biosensor system includes two biosensing techniques on a single device: resonant frequency measurements and electric cell-substrate impedance sensing (ECIS). The multiparametric sensor system is based on the innovative use of the upper electrode of a quartz crystal microbalance (QCM) resonator as working electrode for the ECIS technique. The QCM acoustic wave sensor consists of a thin AT-cut quartz substrate with two gold electrodes on opposite sides. For integration of the QCM with the ECIS technique a semicircular counter electrode was fabricated near the upper electrode on the same side of the quartz crystal. Bovine aortic endothelial live cells (BAECs) were successfully cultured on this hybrid biosensor. Finite element modeling of the bulk acoustic wave resonator using COMSOL simulations was performed. Simultaneous gravimetric and impedimetric measurements performed over a period of time on the same cell culture were conducted to validate the devices sensitivity. The time necessary for the BAEC cells to attach and form a compact monolayer on the biosensor was 35∼45 minutes for 1.5 × 104 cells/cm2 BAECs; 60 minutes for 2.0 × 104 cells/cm2 BAECs; 70 minutes for 3.0 × 104 cells/cm2 BAECs; and 100 minutes for 5.0 × 104 cells/cm2 BAECs. It was demonstrated that this time is the same for both gravimetric and impedimetric measurements. This hybrid biosensor will be employed in the future for water toxicity detection.

Electrical cell-substrate impedance sensing (ECIS) based biosensor for characterization of DF-1 cells

Electric cell-substrate impedance sensing (ECIS) method can be used as a valuable tool for real time monitoring of cell behavior such as attachment, mobility, and growth. Changes in impedance of the cells due to growth and attachment can be modeled as an equivalent circuit consisting of resistors and capacitors of both the cell culture media and the cells. In this work, a biosensor which measures the impedance in DF-1 cells (derived from chicken embroyonic fibroblasts and CEF cells) are presented. The biosensor consists of a Teflon cell holder and two gold electrodes. Experimental measurements were conducted using DF-1 cells cultured in DMEM media. Two different experiments were conducted namely; the control experiment (holder contains only DMEM media) and the cell experiment (holder contains both DMEM media and cells). The biosensor was placed in an incubator with optimum settings for cell growth. Impedance measurements were sampled at six hour intervals. Based on these measurements the resistance and capacitance change due to the growth of the DF-1 cells were calculated. It was observed that significant change in resistance and capacitance values occurs in the first six hours, where cell growth and attachment is most active. After this period of time, the cells become confluent and capacitance values become saturated.

Design of a pierce oscillator for CMOS SAW resonator

Development of microelectromechanical system (MEMS) based oscillators have drawn significant attention because it provides CMOS compatibility and multifrequency operations on a single chip. Recently, integrated MEMS resonators have shown great performance by attaining high quality factors and high frequency operations of up to the GHz range. Of interest, is fully integrated SAW resonator which can be connected to an oscillator circuit on the same chip. For oscillator circuit simulations, the CMOS SAW resonator was modeled using its RLC equivalent circuits. The insertion loss of CMOS SAW resonator used in this design is 35.8dB, with motional resistance Rx=8.95kΩ and the motional capacitance and inductance are Cx=199aF and Lx=350uH. For a MEMS resonator to be able to function as an oscillator it needs to be coupled with supporting circuits. There are various types of supporting oscillator circuit topologies namely the pierce oscillator, differential amplifier oscillator or the transimpedance amplifier circuit topology. The topology to be chosen depends on the design requirement, the loop gain of 1 and the zero phase shifts. For this work, the pierce circuit topology was chosen due to its simplicity and high frequency stability. This simple circuit comprising of 4 transistors, helps to achieve low power consumption and excellent phase noise characteristics. This paper will present the analysis, design and the simulation result of a high gain (>; 36dB) and low power pierce circuit topology for MEMS CMOS SAW resonator. The circuit was designed in 0.18um CMOS technology and yield open loop gain >; 36dB.

Design and modeling of MEMS SAW resonator on Lithium Niobate

Surface Acoustic Wave (SAW) resonators are essential components for modern communication systems. They can function as filters and frequency synthesizers. SAW resonators operate based on the principle of acoustic waves propagating along the surface of a solid piezoelectric material. The waves are generated by injecting electrical energy using interdigitated transducers (IDTs) into the piezoelectric material which transforms it into propagating mechanical waves. This project intends to study the key design parameters that affect the performance of SAW resonator such as optimum spacing between IDT and reflector, optimum spacing of IDTs and the numbers of reflector in order to get the highest mechanical displacement. Key requirements of a SAW resonator include having precise resonant frequency (fr), low insertion losses, and high quality factors (Q). To meet these requirements, it is necessary to investigate the key design parameters; number of reflectors, number of IDTs, periodic distance of transducer fingers (λ), spacing between IDT and reflector. Finite element simulations to determine the optimum SAW resonator design was performed using COMSOL Multiphysics™.

Highly sensitive Escherichia coli shear horizontal surface acoustic wave biosensor with silicon dioxide nanostructures

Surface acoustic wave mediated transductions have been widely used in the sensors and actuators applications. In this study, a shear horizontal surface acoustic wave (SHSAW) was used for the detection of food pathogenic Escherichia coli O157:H7 (E.coli O157:H7), a dangerous strain among 225 E. coli unique serotypes. A few cells of this bacterium are able to cause young children to be most vulnerable to serious complications. Presence of higher than 1cfu E.coli O157:H7 in 25g of food has been considered as a dangerous level. The SHSAW biosensor was fabricated on 64° YX LiNbO3 substrate. Its sensitivity was enhanced by depositing 130.5nm thin layer of SiO2 nanostructures with particle size lesser than 70nm. The nanostructures act both as a waveguide as well as a physical surface modification of the sensor prior to biomolecular immobilization. A specific DNA sequence from E. coli O157:H7 having 22 mers as an amine-terminated probe ssDNA was immobilized on the thin film sensing area through chemical functionalization [(CHO-(CH2)3-CHO) and APTES; NH2-(CH2)3-Si(OC2H5)3]. The high-performance of sensor was shown with the specific oligonucleotide target and attained the sensitivity of 0.6439nM/0.1kHz and detection limit was down to 1.8femto-molar (1.8×10-15M). Further evidence was provided by specificity analysis using single mismatched and complementary oligonucleotide sequences.

A low-cost first-order sigma-delta converter design and analysis

This paper presents the design and analysis of an interface circuit for MEMS or biomedical sensor applications. This circuitry performs the function of an analog-to-digital converter. A first-order 1-bit sigma-delta (Σ-Δ) analog-to-digital converter is designed and simulated using Silterra 0.13μm CMOS process technology with power supply of 1.2V through Cadence. Then the circuit simulation results are transferred to MATLAB, in order to get the frequency domain power spectral density (PSD). The simulation results on noise and error analysis are compared with those from a traditional analog-to-digital converter to prove that sigma-delta is performing better in the case of weak signals acquisition.

Cytotoxicity studies of lung cancer cells using impedance biosensor

Electrical cell-substrate impedance sensing (ECIS) is a valuable tool for real time monitoring of cell behavior such as attachment, mobility, and growth. To employ ECIS, the cells need to attach, spread and proliferate on the sensor in the presence of adhesion-promoting protein that mimics the extracellular matrix (ECM) of the cells. For cell attachment, collagen I, Bovine had been used as the coating substrate. In this study, four designs with varying electrode distances had been measured to detect the changes in impedance values of Lung Carcinoma cell lines (A549). The impedance change due to the cell growth and attachment was modeled as an equivalent circuit consisting of resistors and capacitors of both the cell culture media and the cells. The impedance measurements were measured every 8 hours for 120 hours at frequencies of 100Hz to 10MHz using Agilent Precision Impedance Analyzer 4294A. The experimental results have shown that the closest distance of the electrode gave the most optimum impedance value for A549 cancer cells measurement. The cancer cells were also treated with a chemotherapeutic drug, Taxol and its impedance response was monitored over 5 days. Experimental results show that there is significant reduction in impedance when the cancer cells were exposed to Taxol, indicating that the cells are no longer adherent to the sensors surface or are dead.

Design and optimization of a low-voltage shunt capacitive RF-MEMS switch

This paper presents the design, optimization and simulation of a radio frequency (RF) micro-electromechanical system (MEMS) switch. The device is a capacitive shunt-connection switch, which uses four folded beams to support a big membrane above the signal transmission line. Another four straight beams provide the bias voltage. The switch is designed in 0.35μm complementary metal oxide semiconductor (CMOS) process and is electrostatically actuated by a low pull-in voltage of 2.9V. Taguchi Method is employed to optimize the geometric parameters of the beams, in order to obtain a low spring constant and a robust design. The pull-in voltage, vertical displacement, and maximum von Mises stress distribution was simulated using finite element modeling (FEM) simulation - IntelliSuite v8.7® software. With Pareto ANOVA technique, the percentage contribution of each geometric parameter to the spring constant and stress distribution was calculated; and then the optimized parameters were got as t=0.877μm, w=4μm, L1=40μm, L2=50μm and L3=70μm. RF performance of the switch was simulated by AWR Design Environment 10® and yielded isolation and insertion loss of -23dB and -9.2dB respectively at 55GHz.

Design and analysis of a low-voltage electrostatic actuated RF CMOS-MEMS switch

This paper presents the design and analysis of a radio frequency (RF) micro-electromechanical system (MEMS) switch with low actuation voltage using MIMOS 0.35μm complementary metal oxide semiconductor (CMOS) process. The advantage of this RF MEMS switch is very low actuation voltage design which is compatible with other CMOS circuit without employing a separate on-chip voltage source or charge pump unit. Moreover, using CMOS technology to design can highly simplify the fabrication process, reduce the cost and improve the device performance. The RF MEMS switch is a capacitive shunt-connection type device which uses four folded beams to support a big membrane above the signal transmission line. The pull-in voltage, von Mises stress distribution and vertical displacement of the membrane, up-state and down-state capacitances, as well as the switch impedance is calculated and analyzed by finite element modelling (FEM) simulation.