Kata Jaruwongrungsee

A review of monolithic multichannel quartz crystal microbalance: a review.

Monolithic multichannel quartz crystal microbalance (MQCM) is an emerging technology for advanced sensing and measurement applications. In this report, a comprehensive review of MQCM technology is presented. Firstly, basic MQCMs design, simulation and characterization with emphasis on acoustic interference are described. Next, various MQCM schemes to minimize interference and enhance sensitivity of conventional MQCM devices based on modification of quartz substrate structure are digested. These include mesa, convex and x-axis inversion structures. Three important MQCM sensing platforms and their application areas are then discussed. These comprise MQCM as a static multichannel detector, series MQCM as a multichannel detector for the flow injection analysis and multi-frequency QCM for multi-sensitivity/multi-dynamic range detection. Finally, potential MQCM applications including electronic noses, bio-sensor arrays, and photocatatalytic measurement are illustrated and prospective MQCM applications including electronic tongues and electrochemical measurement are suggested.

Metamaterial-Inspired Multichannel Thin-Film Sensor

A multichannel thin-film sensor is implemented from a set of microstrip-coupled split-ring resonators (SRRs) with different dimensions. Each SRR exhibits a unique high-Q resonance that is sensitive to the presence of a sample in a particular area. Hence, this SRR-based sensor can function (i) to detect different samples simultaneously to increase the throughput or (ii) to characterise nominally identical samples at multiple frequencies to increase the sensor selectivity. In addition, the sensitivity of this SRR-based sensor is optimized through strategic design of the resonator shape to produce a strong confined electric field at each sensing region. The design principle is validated with simulation and measurement. Owing to the optimized design, sensing a low-permittivity film with a thickness as small as one thousandth of the operating wavelength is achievable.

Flow injection based microfluidic device with carbon nanotube electrode for rapid salbutamol detection

A microfabicated flow injection device has been developed for in-channel electrochemical detection (ECD) of a beta-agonist, namely salbutamol. The microfluidic system consists of PDMS (polydimethylsiloxane) microchannel and electrochemical electrodes formed on glass substrate. The carbon nanotube (CNT) on gold layer as working electrode, silver as reference electrode and platinum as auxiliary electrode were deposited on a glass substrate. Silver, platinum, gold and stainless steel catalyst layers were coated by DC-sputtering. CNTs were then grown on the glass substance by thermal chemical vapor deposition (CVD) with gravity effect and water-assisted etching. 100-microm-deep and 500-microm-wide PDMS microchannels fabricated by SU-8 molding and casting were then bonded on glass substrate by oxygen plasma treatment. Flow injection and ECD of salbutamol was performed with the amperometric detection mode for in-channel detection of salbutamol. The influences of flow rate, injection volume, and detection potential on the response of current signal were optimized. Analytical characteristics, such as sensitivity, repeatability and dynamic range have been evaluated. Fast and highly sensitive detection of salbutamol have been achieved. Thus, the proposed combination of the efficient CNT electrode and miniaturized lab-on-a-chip is a powerful platform for beta-agonists detection.

Real-time multianalyte biosensors based on interference-free multichannel monolithic quartz crystal microbalance

In this work, we design, fabricate and characterize a new interference-free multichannel monolithic quartz crystal microbalance (MQCM) platform for bio-sensing applications. Firstly, interference due to thickness-shear vibration mode coupling between channels in MQCM array is effectively suppressed by interposing a polydimethylsiloxane wall between adjacent QCM electrodes on a quartz substrate to form inverted-mesa-like structure. In addition, the electrical coupling due to the electrical impedance of solution is diminished by extending the flow path between them with an extended-design flow channel. The electrical testing results show that individual QCM signal is unaffected by those of adjacent channels under liquid loading, signifying the achievement of interference-free MQCM. The MQCM is applied for multi-analyte biosensing of IgG and HSA. The anti-IgG and anti-HSA are separately immobilized on two adjacent QCM electrodes, which are subsequently blocked with BSA to avoid unspecific binding. The MQCM biosensors are tested with single- and double-analyte solutions under continuous flow of buffer. The IgG and HSA QCM sensors only show frequency shift responses to their corresponding analytes and there are very small cross frequency shifts due to remnant unspecific binding. Moreover, MQCM sensors show approximately linear frequency shift response with analyte concentration. Therefore, the developed MQCM platform is promising for real-time interference-free label-free detection and quantification of multiple bio-analytes.

Metamaterial-inspired microfluidic-based sensor for chemical discrimination

This work proposes a metamaterial-inspired microfluidic-based chemical sensor. The sensor comprises a microwave split-ring resonator (SRR), an important building block of metamaterials, integrated with a disposable flow-channel made of a transparency film. The electromagnetic response of the sensor is observed in the presence of various analytes including glycerol, ethanol, and phosphate buffered saline. It is found that the resonance frequency in the transmission amplitude and the zero crossing in the reflection phase of the sensor are good features for discrimination of these analytes and for determining their concentrations. The developed metamaterial-inspired microfluidic-based chemical sensor has a potential for advanced chemical sensing applications.

High-sensitivity humidity sensor utilizing PEDOT/PSS printed quartz crystal microbalance

In this work, quartz crystal microbalance humidity sensor was fabricated by inkjet printing technique. Poly (3, 4-ethylenedioxythiophene)/poly-styrene-sulfonic acid (PEDOT/PSS), one of the most widely used polymer composites, was printed on QCM electrode as sensing layer using Dimatrix material inkjet printer. The main advantage of this coating method is its high precision of solution coating with accurately controlled volume and area. The printed layer was varied from 1 to 20 layers. With 20 PEDOT/PSS printed layers, the humidity sensitivity is found increased by more than three orders of magnitude compared to uncoated QCM. In addition, the PEDOT/PSS coated QCM exhibits fast humidity detection with short response and recovery times. Thus, the PEDOT/PSS printed on the QCM electrode is an effective way to improve humidity-sensing characteristic of QCM.

Symmetrical PolyMUMPs-Based Piezoresistive Microcantilever Sensors With On-Chip Temperature Compensation for Microfluidics Applications

Microelectromechanical systems (MEMS)-based cantilever beam sensors for microfluidics applications with on-chip temperature sensors for temperature drift compensation were developed. The stress induced on gold surface with polysilicon piezoresistive sensing is demonstrated. In principle, adsorption of biochemical species on a functionalized surface of the microfabricated cantilever will cause surface stress and, consequently, cantilever bending. The sensing mechanism relies on the piezoresistive properties of the doped polysilicon wire encapsulated in the beam. The beam is constructed through multiusers MEMS Process (PolyMUMPs) foundry with postprocessing silicon etching. Bending analysis is performed so that the beam tip deflection can be predicted. The piezoresistor designs on the beams were varied, within certain constraints, so that the sensitivity of the sensing technique could be measured by external read-out circuit. The mass detection of 0.0058-0.0110 g is measured by the beam resistor series as a balanced Wheatstone bridge configuration. The voltage output of the bridge is directly proportional to the amount of bending in the MEMS cantilever. The temperature dependency and sensor performance have been characterized in experiments. Compensation by resisters on the substrate significantly reduces the temperature dependence.

Quartz Crystal Microbalance humidity sensor using electrospun PANI micro/nano dots

In this work, electrospun polyaniline (PANI) micro/nano dots on quartz crystal microbalance (QCM) sensor were used to sense the humidity at room temperature. A QCM humidity sensor is made by coating a low-cost commercial quartz crystal resonator with Polyaniline (PANI), which is one of the most promising polymers for sensing applications due to its relatively high stability. The electrospinning technique is used to coat the PANI nanometer-scale thin film to the electrode of quartz crystal. From experimental results, it was found that PANI coating on the QCM electrode is an effective way to improve humidity-sensing characteristic of QCM sensor. The PANI coated sensor has good response to the humidity with short response and recovery times. The experimental results show that the humidity sensitivity of PANI coated QCM sensor considerably depends on the thickness of PANI layer coated on the sensor electrode.

Real-time and label-free biosensing with microfluidic-based split-ring-resonator sensor

In this work, a split ring resonator (SRR), the most important building block of metamaterial, is fabricated and integrated with a microfluidic chamber for biosensing. The SRR is patterned on a microwave printed circuit board while the microfluidic chamber is fabricated by casting of polydimethylsiloxane (PDMS). SRR was immobilized with Anti-Immunoglobulin G (IgG) for IgG detection by a standard covalent immobilization using Cystamine. The PDMS chamber was aligned and clamped on the circuit board and the electromagnetic response of the SRR sensor was continuously monitored when IgG analytes was flowed through the chamber. The reaction of Immunoglobulin G (IgG) and Anti-IgG results in a shift of resonance frequency. It was found that the response of the resonance frequency is sensitive to the IgG concentrations. Therefore, the SRR microfluidic scheme can be effectively used as an advanced bio-sensing device.

Comparison Study of Ultrasonic Diffraction Tomography and Ultrasonic Non-Diffraction Tomography

Diffraction tomography is a technique for imaging with acoustic fields in which parameter, such as reflective index, sound velocity, etc., can be mapped from scatter wave resulting from insonifying the object with a plane wave at a single temporal frequency. By solving the direct scattering problem, the scattered field can be presented in term of scattering parameters. Different inversion techniques can be applied to takes advantage of the linearization process of the nonlinear wave equation describing wave propagation in heterogeneous media under for limited class of scattering. Specifically, when the scattering effect is weak, one can invoke the Born or Rytov approximation and thus derive the generalized Fourier Slice Theorem to reconstruct the cross-section of the insonified object. The objective of this paper is to compare the quality of the reconstructed image derived from diffraction tomography and non-diffraction tomography.