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On-chip integrated multiple microelectromechanical resonators to enable the local heating, mixing and viscosity sensing for chemical reactions in a droplet

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Abstract

On-chip integrating several functional components for developing integrated lab-on-a-chip microsystem remains as a challenge. In this work, by employing multiple microelectromechanical resonators both as actuators and sensors, on-chip heating, mixing and chemical reaction monitoring are successfully demonstrated. Mechanism studies using COMSOL simulations indicate that the local heating and mixing are induced by the acoustic wave attenuation during its transmission in liquid. On-line chemical reaction monitoring is realized by viscosity sensing using the same resonator through impedance analysis. Classic Diels-Alder reaction in a single droplet was performed to verify the feasibility of using such microsystem for mixing, heating and online reaction monitoring at microscale.

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... So far, ultrahigh frequency acoustofluidics has rarely been studied owing to the lack of such high-frequencya coustic devices.Inthis work, we report amethod for controlling both loading and release of materials into and from vesicles without damaging their structures using the gigahertz (GHz) acoustic streaming generated by at hin film-based nanoelectromechanical (NEMS) resonator.S uch resonators have recently been reported by us to generate high-speed (> ms À1 ) acoustic streaming with strong forces (> nn), which has been applied to enhance the solution mixing in microfluidic chips [39] and to remove nonspecific binding at solid-liquid interfaces. [40] Since acoustic streaming can exert mechanical forces on cells that are immobilized at the solid-liquid interface, [41] we envisaged that vesicles,w hich are soft and hollow structures,w ould also be affected and could experience mechanical deformation under such acoustic stimulation. ...
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In this paper, we present the analytical study of thin film bulk acoustic wave resonators (FBARs) using ZnO and AlN films with a c-axis tilt angle (off-normal) from 0° to 180°. The tilted c-axis orientation induces normal plane and inplane polarizations, which leads to the coexistence of the longitudinal mode and shear mode in the resonator. The equation for predicting electric impedance of FBARs was derived from the basic piezoelectric constitutive equations. Material properties including elastic, dielectric, and piezoelectric coefficients, bulk wave properties including acoustic velocity and electromechanical coupling coefficient, and impedance of FBARs were calculated and showed strong dependence on the tilt angle. Interestingly, it was found that for ZnO FBARs, pure thickness longitudinal modes occur at 0° and 65.4°, and pure thickness shear modes occur at 43° and 90°. For AlN FBARs, pure longitudinal modes occur at 0° and 67.1°, and pure shear modes occur at 46.1° and 90° for AlN. In other words, pure thickness longitudinal and shear modes exist in ZnO and AlN FBARs at specific tilted polarization angles. In addition, two peaks of shear mode electromechanical coefficient are found at 33.3° and 90° for ZnO, and 34.5° and 90° for AlN. Therefore, ZnO and AlN films with specific tilt angles may provide options in the design and fabrication of FBARs, considering their strong shear resonance with high electromechanical coefficients. The use of dual-mode FBARs for mass sensors is also analyzed; the calculated large resonant frequency shift caused by mass loading shows that they have good prospects for use in sensor applications with high sensitivity. The simulation results agreed well with the reported experiment results, and can be used for design and application of FBARs.
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Abstract Biosensors based on AlN bulk acoustic wave resonators require shear mode operation to avoid acoustic losses upon analysing liquid samples. To generate shear modes, the microcrystals of the AlN thin film must be uniformly tilted with respect to the normal, yet keeping good piezoelectric properties. In this paper, we demonstrate AlN solidly mounted resonators displaying simultaneously material electromechanical coupling of 3.5% and quality factor (QS) of 250 for the shear mode in air. Upon testing the devices in liquid, QS factor drops to 150, which is still large enough for biosensing applications. We deposit the AlN film with tilted microcrystals using a two-stage off-axis sputtering process that involves the use of a seed layer and an active piezoelectric layer. We have studied the parameters involved in each stage of the deposition and identified the factors that are key to achieve reproducible high-quality films. By comparing this method to off-axis deposition of AlN on randomly rough substrates, we conclude that the latter produces hardly reproducible and lower quality AlN thin films.
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In the past few years, continuous-flow reactors with channel dimensions in the micro- or millimeter region have found widespread application in organic synthesis. The characteristic properties of these reactors are their exceptionally fast heat and mass transfer. In microstructured devices of this type, virtually instantaneous mixing can be achieved for all but the fastest reactions. Similarly, the accumulation of heat, formation of hot spots, and dangers of thermal runaways can be prevented. As a result of the small reactor volumes, the overall safety of the process is significantly improved, even when harsh reaction conditions are used. Thus, microreactor technology offers a unique way to perform ultrafast, exothermic reactions, and allows the execution of reactions which proceed via highly unstable or even explosive intermediates. This Review discusses recent literature examples of continuous-flow organic synthesis where hazardous reactions or extreme process windows have been employed, with a focus on applications of relevance to the preparation of pharmaceuticals. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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The film bulk acoustic resonator (FBAR) is a widely-used MEMS device which can be used as a filter, or as a gravimetric sensor for biochemical or physical sensing. Current device architectures require the use of an acoustic mirror or a freestanding membrane and are fabricated as discrete components. A new architecture is demonstrated which permits fabrication and integration of FBARs on arbitrary substrates. Wave confinement is achieved by fabricating the resonator on a polyimide support layer. Results show when the polymer thickness is greater than a critical value, d, the FBARs have similar performance to devices using alternative architectures. For ZnO FBARs operating at 1.3–2.2 GHz, d is ,9 mm, and the devices have a Q-factor of 470, comparable to 493 for the membrane architecture devices. The polymer support makes the resonators insensitive to the underlying substrate. Yields over 95% have been achieved on roughened silicon, copper and glass.
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Free-flow electrophoresis is an ideal tool for preparative separations in continuous microflow. With the approach presented herein for coupling free-flow electrophoresis and mass spectrometry it is now also possible to trace non-fluorescent compounds and identify them by means of mass spectrometry. The functionality of the method and its potential as an integrated separation unit for microflow synthesis is demonstrated by application to a multicomponent [3+2]-cycloannulation.
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The combination of ultrasound and microreactor is an emerging and promising area, but the report of designing high-power ultrasonic microreactor (USMR) is still limited. This work presents a robust, high-power and highly efficient USMR by directly coupling a microreactor plate with a Langevin-type transducer. The USMR is designed as a longitudinal half wavelength resonator, for which the antinode plane of the highest sound intensity is located at the microreactor. According to one dimension design theory, numerical simulation and impedance analysis, a USMR with a maximum power of 100 W and a resonance frequency of 20 kHz was built. The strong and uniform sound field in the USMR was then applied to intensify gas-liquid mass transfer of slug flow in a microfluidic channel. Non-inertial cavitation with multiple surface wave oscillation was excited on the slug bubbles, enhancing the overall mass transfer coefficient by 3.3-5.7 times.
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Microreactor technology has gained significant popularity in the chemical and process industry in the past decade. The development of microreactors either as innovative production units for chemical synthesis or as promising laboratory tools for reaction and kinetic studies relies highly on the capability of performing online analyses, which opens great opportunities for the integration of spectroscopic detection techniques. This paper gives an overview of the state-of-the-art in the combination of microreactors with spectroscopic analyses for online reaction monitoring and catalyst characterization. In this upcoming field, many studies have been carried out combining fluorescence, ultraviolet–visible, infrared, Raman, X-ray, and nuclear magnetic resonance spectroscopy. Current research progress is reviewed, with emphasis on the existing integration schemes and selected application examples that demonstrate the potential of online spectroscopic detection for rapid microreactor process analysis and optimization. An outlook on the future development in this area is also presented.
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A series of tubes: The continuous manufacture of a finished drug product starting from chemical intermediates is reported. The continuous pilot-scale plant used a novel route that incorporated many advantages of continuous-flow processes to produce active pharmaceutical ingredients and the drug product in one integrated system.
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Hot chemistry! High-frequency inductive heating and flow chemistry are an ideal match for high-temperature synthesis. This is demonstrated in the multistep flow synthesis of the neurolepticum olanzapine (Zyprexa) that included three reactions with inductive heating and two purification steps conducted as continuous processes.
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The nucleation process of CdSe nanocrystals is studied by fluorescence-detected extended x-ray absorption fine structure (EXAFS) using a microreactor and synchrotron radiation. Detailed analysis of in situ Se K-edge EXAFS data measured along a microreactor channel revealed a strong position-dependence which displays a rapid increase in the CdSe phase with time at the initial stage. The results indicate that the CdSe nucleation completes within several seconds starting from trioctylphosphine Se solution and dodecylamine surfactant at 240 °C. This shows the promising capability of in situ EXAFS combined with a microreactor to investigate the nucleation process of nanocrystals synthesized in a solvent.
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Exact time-correlation formulas for frequency-dependent shear viscosity, bulk viscosity, and thermal conductivity are presented. These formulas are evaluated for a fluid composed of molecules with internal degrees of freedom, in the limit of very weak coupling of internal and translational motions. In this limit, the shear viscosity is unaffected by internal modes. The bulk viscosity consists of two parts, one due to translational motions, and the other due to relaxation of the energy contained in internal modes. The thermal conductivity consists of two parts, one due to translational motions, and the other due to diffusion of energy in internal modes (the Eucken correction). The resulting excess sound absorption is in complete agreement with the predictions of the thermodynamic theory of relaxation in fluids.
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The ozonolysis of 1-decene (1) was performed in a falling film microreactor and in a semibatch reactor using different solvents (CH2Cl2, CH3OH, or a mixture of both). The main products of ozonolysis were 3-octyl-1,2,4-trioxolane (7) in CH2Cl2 and 1-hydroperoxy-1-methoxynonane (8) in CH3OH or in a CH2Cl2/CH3OH mixture. In both cases the selectivities were higher than 70% and almost independent of 1-decene conversion and reaction temperature. The ozonolysis proceeds mainly via the cleavage of the primary ozonide into the long-chain carbonyl oxide (6) and formaldehyde (4). Besides off-line analysis in situ ATR-FTIR spectroscopic measurements using a diamond ATR probe were applied to follow the reaction progress. Integral intensities of characteristic IR bands correlate well with quantitative results obtained from gas chromatography/high-performance liquid chromatography analysis. Thus, in situ ATR proved to be a suitable method for fast and real-time monitoring of liquid-phase reactions even in the presence of unstable or explosive intermediates like ozonides and/or hydroperoxides.
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In this work, a new controllable and continuous free radical polymerization process was developed and characterized in a coaxial capillary microreactor. In this process, the monomer solution was first dispersed into monodispersed droplets followed by thermal-initiated polymerization in the following capillary immersed in an oil bath. Poly(butyl acrylate) prepared in this microreactor possessed a much higher average molecular weight (Mn) and far lower polydispersity index (PDI) than that produced in a typical stirred vessel. The microreactor method possesses two unique advantages which allow for the optimization of the free radical polymerization process. First, the use of highly monodispersed droplets as polymerization units ensures that the polymerization process occurs uniformly in each individual droplet. Second, the small droplet size, on the order of several hundred micrometers, greatly enhances heat transfer efficiency with no heat accumulation within the droplets during polymerization. A simplified numerical simulation was used to show the superiority of the microreactor in effectively removing polymerization heat due to the miniaturization of the droplets to submillimeter scale. Simulation results also demonstrated that, in contrast to polymerization processes occurring in macroreactors, the polymerization conducted in the microreactor proceeded in a nearly isothermal condition. Experimental results in the microreactor showed that the molecular weight distribution was mainly determined by the size of the droplet, while the molecular weight of the polymer could be adjusted by changing the reaction temperature and 2,2-azobis(isobutyronitrile) concentration. This type of microreactor can potentially be applied to research involving the mechanisms of highly exothermic free radical polymerization processes and can also be used as an efficient tool for their controllable preparation.
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A microscale chemistry improvement engine: a pre-dosed microscale high-throughput experimentation additives platform enables rapid, serendipitous reaction improvement. This platform allowed one chemist to set up 475 experiments and analyze the results using MISER chromatography in a single day, thus resulting in two high-quality catalytic systems for the construction of the title compound 1. Support for a single-electron transfer mechanism was obtained.
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Film bulk acoustic resonators (FBAR) vibrating in shear mode and operating at around 830 MHz have been fabricated. They were tested in air and water–glycerol solutions. With a sensitivity of 1 kHz cm2/ng, these devices are attractive for gravimetric sensing applications. The FBARs are solidly mounted on acoustic mirrors and use 16° c-axis inclined ZnO thin films realized by reactive sputtering. An analysis of the performance in liquids with different viscosities has been done and the effect on quality factor and resonance frequency has been shown. Effective coupling coefficients of up to 1.7% and quality factors of up to 380 and 199 were determined in air and deionized water, respectively. The obtained characteristics are sufficient for gravimetric sensing applications in liquid environments and the FBARs can be used as high frequency viscosity sensors for liquids of viscosities up to 10 mPa s.
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In this paper, we present a liquid-droplet-heating system using a surface acoustic wave (SAW) device. When liquid is placed on a Rayleigh-SAW-propagating surface, a longitudinal wave is radiated into the liquid. If the SAW amplitude increases, the liquid shows non-linear dynamics, such as vibrating, streaming, small droplet flying, and atomizing. This phenomenon is well known as SAW streaming. The liquid temperature is measured during the longitudinal wave radiation and found to increase. First, the mechanism of the liquid-heating effect is discussed on the basis of experimental results. The surface electrical condition is changed to investigate the effect of dielectric heating. The obtained results indicate that the radiated longitudinal wave causes liquid heating and the dielectric heating effect does not. Second, the fundamental properties of the liquid temperature are measured by varying the applied voltage, duty factor, and liquid viscosity. The liquid temperature is found to be proportional to the duty factor and the square of the applied voltage. Therefore, the liquid temperature can be controlled by these applied signals. Also, by using highly viscous solutions, the liquid temperature is increased to more than 100 °C. Moreover, for chemical applications, the possibility of periodic temperature control is tested by varying the duty factor. The obtained results strongly suggest that an efficient thermal cycler is realized. A novel application of the SAW device is proposed on the basis of SAW streaming.
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Piezoelectric microelectromechanical systems (MEMS) resonant sensors, known for their excellent mass resolution, have been studied for many applications, including DNA hybridization, protein-ligand interactions, and immunosensor development. They have also been explored for detecting antigens, organic gas, toxic ions, and explosives. Most piezoelectric MEMS resonant sensors are acoustic sensors (with specific coating layers) that enable selective and label-free detection of biological events in real time. These label-free technologies have recently garnered significant attention for their sensitive and quantitative multi-parameter analysis of biological systems. Since piezoelectric MEMS resonant sensors do more than transform analyte mass or thickness into an electrical signal (e.g., frequency and impedance), special attention must be paid to their potential beyond microweighing, such as measuring elastic and viscous properties, and several types of sensors currently under development operate at different resonant modes (i.e., thickness extensional mode, thickness shear mode, lateral extensional mode, flexural mode, etc.). In this review, we provide an overview of recent developments in micromachined resonant sensors and activities relating to biochemical interfaces for acoustic sensors.
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Superparamagnetic nanoparticles coated with silica gel or alternatively steel beads are new fixed-bed materials for flow reactors that efficiently heat reaction mixtures in an inductive field under flow conditions. The scope and limitations of these novel heating materials are investigated in comparison with conventional and microwave heating. The results suggest that inductive heating can be compared to microwave heating with respect to rate acceleration. It is also demonstrated that a very large diversity of different reactions can be performed under flow conditions by using inductively heated flow reactors. These include transfer hydrogenations, heterocyclic condensations, pericyclic reactions, organometallic reactions, multicomponent reactions, reductive cyclizations, homogeneous and heterogeneous transition-metal catalysis. Silica-coated iron oxide nanoparticles are stable under many chemical conditions and the silica shell could be utilized for further functionalization with Pd nanoparticles, rendering catalytically active heatable iron oxide particles.
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Microdroplets in microfluidics offer a great number of opportunities in chemical and biological research. They provide a compartment in which species or reactions can be isolated, they are monodisperse and therefore suitable for quantitative studies, they offer the possibility to work with extremely small volumes, single cells, or single molecules, and are suitable for high-throughput experiments. The aim of this Review is to show the importance of these features in enabling new experiments in biology and chemistry. The recent advances in device fabrication are highlighted as are the remaining technological challenges. Examples are presented to show how compartmentalization, monodispersity, single-molecule sensitivity, and high throughput have been exploited in experiments that would have been extremely difficult outside the microfluidics platform.
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We report high-speed real-time PCR performed on an unmodified disposable polystyrene Petri dish. The reaction cycle relies solely on an infrared laser for heating; no conventional heater is required. Nanoliter droplets of PCR mixture as water-in-oil emulsions printed in an array format served as individual PCR microreactors. A simple contact printing technique was developed to generate a large array of uniform sized nanoliter droplets using disposable pipette tips. Printed droplets showed variation of less than 10% in volume and the oil/water/polystyrene interface formed a compact droplet microreactor approximately spherical in shape. The uniform droplet array was used to optimize the laser power required for the two heating steps of PCR, annealing/extension and melting, while the ambient conditions were at room temperature. The optical heating allows for an extremely fast heating rate due to the selective absorption of the infrared laser by PCR buffer only and not the oil or polystyrene Petri dish, allowing completion of 40 amplification cycles in approximately 6 minutes. The quantitative assay capability of the system is also presented and discussed.
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The philosophy of miniature total analysis systems (mu-TAS) hinges on the integration of multiple chemical processing steps and the means of analyzing their results on the same miniaturized system. We have constructed chip-based capillary electrophoresis (CE) devices equipped with an integrated planar radio-frequency detector coil used for nuclear magnetic resonance spectroscopy (NMR). Separations were accomplished in the devices, but satisfactory NMR spectra could only be obtained from samples of high concentration. The relative sensitivity is explained and the scaling law dichotomy of CE and NMR explored.
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Fourier transform infrared (FT-IR) spectroscopy in a multiple internal reflection (MIR) geometry is integrated with silicon-based microreactors to allow detection of a wide range of chemical species while taking advantage of inexpensive batch fabrication techniques applicable to silicon substrates. The microreactors are fabricated in silicon and glass using standard microfabrication and selective etching techniques. The small ( approximately 1 cm side) reactor size provides access to nearly the full mid-IR frequency region with MIR-FT-IR, allowing us to probe both solution-phase and surface-bound chemical transformations. The wide applicability of this approach is demonstrated with two representative test cases: kinetics of acid-catalyzed ethyl acetate hydrolysis and amidization of surface-tethered amine groups.
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The advantages of using microreactors for drug and process discovery are discussed. In the microreactor, reagents can be brought in a specific sequence, mixed and allowed to react for a specified time in a controlled region of the channel networks using electrokinetic or hydrodynamic pumping. Performing chemical reactions within a microreactor provides the opportunity to perform real-time operations. Integration of a microreactor device via a purification or separation step with one of the many highly sensitive microchannel-based biological assay systems would provide a drug discovery tool.
Article
A capillary-based flow system has been developed for conducting microscale organic synthesis with the aid of microwave irradiation. The capillary internal diameter investigated ranged from 200 to 1200 mum, while the flow rate was varied between 2 and 40 muL/min, which corresponds to the sample being irradiated approximately 4 min. Other parameters investigated include reaction concentration and power setting of the microwave. Excellent conversion was observed in a variety of cross coupling and ring-closing metathesis (RCM) reactions employing metal catalysts and in nucleophilic aromatic substitution and Wittig reactions that do not employ metals. Reactions that have solids in them do not seem to pose a significant concern for the method, such as blocked channels. It was shown that capillaries coated internally with thin films of Pd metal show tremendous rate accelerations and that the thin films themselves are capable of catalyzing Suzuki-Miyaura reactions with no exogenous catalyst added. Importantly, it has been demonstrated that reagents in separate syringes can be coinjected into the capillary, mix, and react with none of the laminar flow problems that plague microreactor (lab on a chip) technology. This paves the way to use microwave-assisted, flow capillary synthesis as a powerful and efficient means to replace "one-at-a-time" microwave synthesis to provide libraries of compounds in a scale suitable for biological screening purposes.
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Microreactor technology has shown potential for optimizing synthetic efficiency, particularly in preparing sensitive compounds. We achieved the synthesis of an [(18)F]fluoride-radiolabeled molecular imaging probe, 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG), in an integrated microfluidic device. Five sequential processes-[18F]fluoride concentration, water evaporation, radiofluorination, solvent exchange, and hydrolytic deprotection-proceeded with high radio-chemical yield and purity and with shorter synthesis time relative to conventional automated synthesis. Multiple doses of [18F]FDG for positron emission tomography imaging studies in mice were prepared. These results, which constitute a proof of principle for automated multistep syntheses at the nanogram to microgram scale, could be generalized to a range of radiolabeled substrates.
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Fundamental and applied research in chemistry and biology benefits from opportunities provided by droplet-based microfluidic systems. These systems enable the miniaturization of reactions by compartmentalizing reactions in droplets of femoliter to microliter volumes. Compartmentalization in droplets provides rapid mixing of reagents, control of the timing of reactions on timescales from milliseconds to months, control of interfacial properties, and the ability to synthesize and transport solid reagents and products. Droplet-based microfluidics can help to enhance and accelerate chemical and biochemical screening, protein crystallization, enzymatic kinetics, and assays. Moreover, the control provided by droplets in microfluidic devices can lead to new scientific methods and insights.
Article
We demonstrate the fabrication and characterization of a novel, inexpensive microchip capable of laser induced fluorescence (LIF) detection using integrated waveguides with built-in optical filters. Integrated wavelength-selective optical waveguides are fabricated by doping poly(dimethysiloxane) (PDMS) with dye molecules. Liquid-core waveguides are created within dye-doped PDMS microfluidic chips by filling channels with high refractive index liquids. Dye molecules are allowed to diffuse into the liquid core from the surrounding dye-doped PDMS. The amount of diffusion is controlled by choosing either polar (low diffusion) or apolar (high diffusion) liquid waveguide cores. The doping dye is chosen to absorb excitation light and to transmit fluorescence emitted by the sample under test. After 24 h, apolar waveguides demonstrate propagation losses of 120 dB cm(-1) (532 nm) and 4.4 dB cm(-1) (633 nm) while polar waveguides experience losses of 8.2 dB cm(-1) (532 nm) and 1.1 dB cm(-1) (633 nm) where 532 and 633 nm light represent the excitation and fluorescence wavelengths, respectively. We demonstrate the separation and detection of end-labelled DNA fragments using polar waveguides for excitation light delivery and apolar waveguides for fluorescence collection. We demonstrate that the dye-doped waveguides can provide performance comparable to a commercial dielectric filter; however, for the present choice of dye, their ultimate performance is limited by autofluorescence from the dye. Through the detection of a BK virus polymerase chain reaction (PCR) product, we demonstrate that the dye-doped PDMS system is an order of magnitude more sensitive than a similar undoped system (SNR: 138 vs. 9) without the use of any external optical filters at the detector.
Article
This paper describes a highly sensitive, film bulk acoustic resonator (FBAR) mass sensor (built on a micromachined silicon-nitride diaphragm with a piezoelectric thin film and Al electrodes) that can operate in vapor and liquid. The sensitivity of the device to mass change on its surface has been investigated by having various thicknesses of silicon-nitride support layer and also of Al layer. The sensor is measured to have a mass sensitivity of 726 cm $^2$ /g, which is about 50 times that of a typical quartz crystal microbalance (QCM). In vapor, the sensor (operating at around 1 GHz and having a relatively high quality (Q) factor of 200–300) shows a minimum detectable frequency shift of about 400 Hz, which corresponds to a mass change of $10^-9$ g/cm $^2$ on the sensor surface, comparable with that detectable by a QCM. In liquid, though the Q usually drops more than an order of magnitude, we obtain a Q of 40 at 2 GHz by using a second harmonic resonance of the resonator. And with the Q, a minimum 5 ppm resonant frequency shift can be detected, which corresponds to $10^- 8$ g/cm $^2$ change on the sensor surface. hfillhbox[1374]
Article
We report the development of a micromachined magnetic-bar micromixer for microscale fluid mixing in biological laboratory-on-a-chip applications. The mixer design is inspired by large scale magnetic bar mixers. A rotating magnetic field causes a single magnetic bar or an array of them to rotate rapidly within a fluid environment. A fabrication process of the magnetic bar mixer is developed. Results of fluid mixing in micro channels and chambers are investigated using experimental means and computer-aided fluid simulation.
Piezoelectric microelectromechanical resonant sensors for chemical and biological detection Online analysis of oxygen inside silicon-glass microreactors with integrated optical sensors
  • H Pang
  • E S Zhao
  • H Kim
  • H Zhang
  • X Yu
  • Hu
(a) W. Pang, H. Zhao, E.S. Kim, H. Zhang, H. Yu, X. Hu, Piezoelectric microelectromechanical resonant sensors for chemical and biological detection, Lab Chip 12 (2012) 29–44; (b) J. Ehgartner, P. Sulzer, T. Burger, A. Kasjanow, D. Bouwes, U. Krühne, I. Klimant, T. Mayr, Online analysis of oxygen inside silicon-glass microreactors with integrated optical sensors, Sens. Actuators B 228 (2016) 748–757.
The effect of perimeter geometry on FBAR resonator electrical performance
  • R Ruby
  • J Larson
  • C Feng
  • S Fazzio
R. Ruby, J. Larson, C. Feng, S. Fazzio, The effect of perimeter geometry on FBAR resonator electrical performance, IEEE MTT-S International Microwave Symposium Digest (2005) 217-220.