An 8-pixel micromachined quartz crystal resonator array with fundamental resonance frequency of 73 MHz has been designed, fabricated and tested for detecting Respiratory Syncytial Virus (RSV) G-gene. We established a protocol for selectively functionalizing the surface of resonator array using electrochemical desorption. The selective functionalization of hydrophobic and hydrophilic surfaces with methyl-and carboxylate- terminated alkanethiols is characterized by Fourier transform spectroscopy (FTIR) and contact angle measurements. QCMs functionalized with hydrophobic and hydrophilic terminations also showed a clearly distinguishable response to ionic (buffer) solution. Thiol modified single-stranded DNA (oligonucleotide probes) were designed for functionalization of the QCM pixel surfaces. Selective desorption of the pixels was achieved via electrochemical methods and was characterized by cyclic voltammogram. The specific detection of RSV G-gene is successfully demonstrated by the frequency response of the QCM pixels and was verified by fluorescence images after hybridization using fluorescently labeled probes. We demonstrate that micromachined quartz crystal resonator arrays could potentially become a convenient DNA array technology that can be used for label-free, quantitative gene assays using extremely small volumes of analytes.

: This report summarizes the design, fabrication, and characterization of thermal infrared (IR) imaging arrays operating at room temperature which are based on Y -cut-quartz bulk acoustic wave resonators. A novel method of tracking the resonance frequency based upon the measurement of impedance is presented. High-frequency (240-MHz) micromachined resonators from Y -cut-quartz crystal cuts were fabricated using heterogeneous integration techniques on a silicon wafer. A temperature sensitivity of 22.16 kHz/deg. C was experimentally measured.IR measurements on the resonator pixel resulted in a noise equivalent power of 3.90 nW/Hz1/2, a detectivity D of 1 * 105 sq cm Hz1/2/W, and a noise equivalent temperature difference of 4 mK in the 8 -14 m wavelength range. The thermal frequency response of the resonator was determined to be faster than 33 Hz, demonstrating its applicability in video-rate uncooled IR imaging. This work represents the first comprehensive thermal characterization of micromachined Y -cut-quartz resonators and their IR sensing response. In addition the report also summarizes the work done on viscoelastic measurements performed using micromachined quartz resonators and quartz etching work undertaken as part of this work.

Self-assembled monolayers (SAMs) of nitrile-substituted oligo(phenylene ethynylene) thiols (NC-OPEn) with a variable chain length n (n ranging from one to three structural units) on Au(111) were studied by synchrotron-based high-resolution X-ray photoelectron spectroscopy and near-edge absorption fine-structure spectroscopy. The experimental data suggest that the NC-OPEn molecules form well-defined SAMs on Au(111), with all the molecules bound to the substrate through the gold–thiolate anchor and the nitrile tail groups located at the SAM–ambient interface. The packing density in these SAMs was found to be close to that of alkanethiolate monolayers on Au(111), independent of the chain length. Similar behavior was found for the molecular inclination, with an average tilt angle of ~33–36° for all the target systems. In contrast, the average twist of the OPEn backbone (planar conformation) was found to depend on the molecular length, being close to 45° for the films comprising the short OPE chains and ~53.5° for the long chains. Analysis of the data suggests that the attachment of the nitrile moiety, which served as a spectroscopic marker group, to the OPEn backbone did not significantly affect the molecular orientation in the SAMs.

This paper presents the design, fabrication, and characterization of thermal infrared (IR) imaging arrays operating at room temperature which are based on Y-cut-quartz bulk acoustic wave resonators. A novel method of tracking the resonance frequency based upon the measurement of impedance is presented. High-frequency (240-MHz) micromachined resonators from Y-cut-quartz crystal cuts were fabricated using heterogeneous integration techniques on a silicon wafer. A temperature sensitivity of 22.16 kHz/°C was experimentally measured. IR measurements on the resonator pixel resulted in a noise equivalent power of 3.90 nW/Hz 1/2 , a detectivity D* of 1 × 10 5 cm · Hz 1/2 /W, and a noise equivalent temperature difference of 4 mK in the 8- to 14-μm wavelength range. The thermal frequency response of the resonator was determined to be faster than 33 Hz, demonstrating its applicability in video-rate uncooled IR imaging. This work represents the first comprehensive thermal characterization of micromachined F-cut-quartz resonators and their IR sensing response.

In this paper, we present a micromachined Y-cut quartz resonator based thermal sensor array which is configured with a reaction chamber that is physically separated but located in close proximity to the resonator for sensitive calorimetric biosensing applications. The coupling of heat from the reaction chamber to the quartz resonator is achieved via radiation and conduction through ambient gas. The sensor was packaged onto a 300 mu m thick stainless plate with an opening in the middle. The sensor array was aligned to the opening and mounted from the underside of the plate. A reaction chamber designed for performing (bio)chemical reactions was used in the measurements. This configuration of the sensor allows for a very robust sensing platform with no fouling of the sensor surface or degradation in its performance metrics. Impedance-based tracking of resonance frequency was used for chemical, enzymatic, and cellular activity measurements. The sensor described has an impedance sensitivity of 852 Omega degrees C-1 or a frequency sensitivity of 7.32 kHz degrees C-1 for the 91 MHz resonator used in this work. Results on exothermic reaction between hydrochloric acid and ammonium hydroxide, the hydrolysis reaction of urea by urease and the catalytic reaction of glucose with glucose dehydrogenase are reported. From the signal to noise ratio analysis of the glucose sensor, <10 mu M glucose sensitivity could be obtained improving the detection limit by a factor of 250 in comparison to our previous work using thermopile sensors. Finally, calcium ionophore induced cellular activity was measured in pancreatic cancer cells using the sensor.

A micromachined Y-cut quartz resonator based thermal biosensor – configured with a reaction chamber that is physically separated but located in close proximity to the resonator for sensitive calorimetric biosensing applications is presented. The coupling of heat from the reaction chamber to the quartz resonator is achieved via radiation and conduction through ambient gas. This configuration of the sensor allows for a very robust sensing platform with no fouling of the sensor surface or degradation in its performance metrics. Frequency based and Impedance-based tracking of resonance frequency was used for chemical and enzymatic activity measurements and compared here. An impedance sensitivity of 852Ω/°C (frequency sensitivity of 7.32kHz/°C) was obtained for the 91MHz.

The maximum capacity of a hydrophobic adsorbent is interpreted in terms of square or hexagonal (cubic and face-centered-cubic, FCC) interfacial packing models of adsorbed blood proteins in a way that accommodates experimental measurements by the solution-depletion method and quartz-crystal-microbalance (QCM) for the human proteins serum albumin (HSA, 66 kDa), immunoglobulin G (IgG, 160 kDa), fibrinogen (Fib, 341 kDa), and immunoglobulin M (IgM, 1000 kDa). A simple analysis shows that adsorbent capacity is capped by a fixed mass/volume (e.g. mg/mL) surface-region (interphase) concentration and not molar concentration. Nearly analytical agreement between the packing models and experiment suggests that, at surface saturation, above-mentioned proteins assemble within the interphase in a manner that approximates a well-ordered array. HSA saturates a hydrophobic adsorbent with the equivalent of a single square or hexagonally-packed layer of hydrated molecules whereas the larger proteins occupy two-or-more layers, depending on the specific protein under consideration and analytical method used to measure adsorbate mass (solution depletion or QCM). Square or hexagonal (cubic and FCC) packing models cannot be clearly distinguished by comparison to experimental data. QCM measurement of adsorbent capacity is shown to be significantly different than that measured by solution depletion for similar hydrophobic adsorbents. The underlying reason is traced to the fact that QCM measures contribution of both core protein, water of hydration, and interphase water whereas solution depletion measures only the contribution of core protein. It is further shown that thickness of the interphase directly measured by QCM systematically exceeds that inferred from solution-depletion measurements, presumably because the static model used to interpret solution depletion does not accurately capture the complexities of the viscoelastic interfacial environment probed by QCM.

In this paper, we use micromachined, high-frequency, quartz bulk acoustic wave resonators to systematically study the physical and viscoelastic properties of spontaneously adsorbed globular protein films with molecular weights (MWs) spanning three decades on hydrophobic surfaces. Specifically, changes in the frequency and the Q -factor of the micromachined resonator array were studied as a function of concentration for five proteins, namely human serum albumin (HSA), immunoglobulin G (IgG), human fibrinogen (Fib), alpha-2-macroglobulin (AMG), and immunoglobulin M (IgM) at the fundamental and third resonance modes. The results obtained were interpreted using equivalent electrical impedance models for the multilayer stack on the quartz crystal microbalances surface. Discrete changes in the protein adsorption and the viscoelastic behavior with solution concentration were observed for all the five protein films. The spherical core-shell protein model is used to provide a simple explanation of the results. The work presents the first systematic and quantitative evaluation of the density, thickness, viscosity, and elastic modulus of adsorbed globular protein films and demonstrates the advantages of using micromachined high-frequency bulk acoustic wave resonators for obtaining these types of data.

This paper presents the design, fabrication, and characterization of temperature sensitive quartz resonators fabricated using heterogeneous integration methods for realizing high-density, thermal conductance fluctuation limited infrared imaging arrays operating at room temperature. High frequency (241 MHz) micromachined resonators from Y-cut quartz crystal cuts were fabricated with a temperature sensitivity of 22.16 kHz/degrees C. Infrared measurements on the resonator pixel resulted in a noise equivalent power (NEP) of 3.90 nW/Hz(1/2), a detectivity D* of 9.17x10(7) cm Hz(1/2)/W, and noise equivalent temperature difference (NETD) of 46.6 mK in the 8-14 mu m wavelength range. The thermal frequency response of the resonator was determined to be faster than 33 Hz, demonstrating its applicability as a video-rate uncooled infrared sensor. (C) 2010 Published by Elsevier Ltd.

This paper presents the design, fabrication, and characterization of temperature sensitive quartz resonators fabricated using heterogeneous integration methods for realizing high-density, thermal conductance fluctuation limited thermal sensors for infrared imaging and biochemical sensing applications. An integrated quartz sensor array using CMOS-compatible micromachining techniques has been designed and fabricated. 241 MHz micromachined resonators from Y-cut quartz crystal cuts were fabricated with a temperature sensitivity of 22.162 kHz/°C. Infrared measurements on the resonator pixel resulted in a noise equivalent power (NEP) of 3.90 nW/Hz 1/2 , detectivity D* of 9.17 ×10 7 cmHz 1/2 /W, and noise equivalent temperature difference (NETD) in the 8-12 μm wavelength region of 4 mK and a response time of <;30 Hz. In a unique new application a remotely coupled thermal sensor configuration was used to monitor biochemical reactions in real time.

In this paper we use micromachined, high-frequency, quartz bulk acoustic wave resonator arrays to evaluate the physical and viscoelastic properties of adsorbed globular protein films with molecular weights spanning two orders of magnitude. Specifically, changes in the frequency and the Q-factor of the micromachined resonator array were studied as a function of concentration for three proteins, namely Human Serum Albumin (HSA), Immunoglobulin G (IgG) and Human Fibrinogen (Fib) at the fundamental and third resonance modes. The results obtained are interpreted using continuum mechanics approach for multilayer stack on the QCM surface. Discrete changes in the protein adsorption rate constant and the viscoelastic behavior was observed for all the three protein films. The thickness, density, elastic modulus and viscosity of protein layer were successfully obtained through this analysis.

The dynamics of the charge transfer (CT) in alkanethiolate self-assembled monolayers is addressed by resonant Auger spectroscopy using the core hole clock method. The CT pathway was unambiguously defined by resonant excitation of the nitrile tailgroup attached to the alkyl backbone. The length of this backbone was varied to monitor the respective dependence of the CT time. It was found that, similar to the static conductance, this dependence can be coarsely described by an exponential function with an attenuation factor of 0.93 per methylene unit (0.72 angstrom(-1); a tunneling along the chain was assumed). As a result, the CT time is quite long even for a relatively short alkyl chain; in particular, it is ca. 100 fs for the chain consisting of only four CH2 units. In contrast, the CT time associated with the thiolate headgroup anchor was found to be quite short, viz. 2.3 fs, which suggests an efficient interfacial electronic coupling between the aliphatic backbone of the CnCN molecules and the substrate over the thiolate-gold linkage.

In this paper we use micromachined, high-frequency, quartz bulk acoustic wave resonators to systematically study the physical and viscoelastic properties of spontaneously adsorbed globular protein films with molecular weights (MW) spanning two orders of magnitude. Specifically, changes in the frequency and the Q-factor of the micromachined resonator array were studied as a function of concentration for three proteins, namely Human Serum albumin (HSA), Immunoglobulin G (IgG) and Human Fibrinogen (Fib) at the fundamental and third resonance modes. The results obtained were interpreted using equivalent electrical impedance models for the multilayer stack on the QCM surface. Discrete changes in the protein adsorption rate constant and the viscoelastic behavior was observed for all the three protein films. The spherical core-shell protein model is used to provide a simple explanation of the results. The work presented is a systematic and quantitative evaluation of the density, thickness, viscosity, and elastic modulus of the globular protein films, which was possible, due the use of the micromachined high frequency bulk acoustic wave resonators.

This paper reviews the fabrication and performance of micromachined quartz resonator arrays. Using inductively coupled plasma etching techniques, we have successfully fabricated micromachined quartz resonator arrays with fundamental frequencies in the range of 25–85 MHz in an array format. These resonators have been experimentally evaluated for their performance in viscous (liquid) and viscoelastic (a biomolecular film in liquid) loading conditions. The paper discusses the ultimate sensitivity to mass and other properties of the adsorbates/contacting materials onto high-frequency quartz resonator surfaces. Measuring the frequency and Q-factor changes at the fundamental and third overtone of a 66 MHz resonator upon adsorption of immunoglobulin G (IgG) protein film on a hexadecanethiol functionalized surface, we were able to deduce: (i) the film thickness = 18 nm, (ii) density = 1040 kg m−3, (iii) elastic modulus = 6.7 MPa and (iv) viscosity = 5.5 mPa s. Furthermore, from the adsorption isotherm for the IgG film, two different Langmuir equilibrium constants (K) were deduced. In the low-concentration region K = 2.13 × 108 M−1 and in the high-concentration region K = 6.53 × 106 M−1 were obtained. The thickness and density values obtained for IgG are consistent with the bilayer model predicted from interfacial packing of spherical protein molecules as a function of the molecular weight, and K values are consistent with earlier reported values for adsorption of IgG films. This is the first reporting of the elastic modulus and viscosity of IgG films in phosphate buffer solution.

Micromachined quartz crystal resonator arrays operating in the 66–69MHz fundamental mode range were tested for their ability to provide high sensitivity to mass loading and viscoelastic properties of biomolecules and biomolecular assemblies. Calibrations using viscous water–glycerol mixtures give the expected linear dependence on the square root of the density–viscosity product. Sequential adsorption of avidin layers interspersed with dithiobis(sulfosuccinimidylpropionate) (DTSSP) or biotynilated bovine albumin (BBA) cross-linker layers provided thick and planar viscoelastic layers for testing. The data reveal a high Q-factor sensitivity and the observed complex impedance changes could be accounted for using a layer dependent, variable viscosity model treated with continuum mechanics approach. The best interpretation of the frequency and Q-factor changes indicates that the layer material properties are most likely dominated by the frictional effects arising from the inter-linking molecules between the layers. These results show the ability of these high frequency micro resonators as an incisive tool for analyzing both static loading and dynamic viscoelastic properties of bimolecular adsorbates.

We have designed and fabricated 25-microm-thick quartz resonators operating at a fundamental resonance frequency of approximately 62 MHz. The results show a substantial increase in the mass sensitivity compared to single monolithic commercial resonators operating at lower frequencies in the approximately 5-10-MHz range. The overall performance of the micromachined resonators is demonstrated for the example of human serum albumin protein adsorption from aqueous buffer solutions onto gold electrodes functionalized with self-assembled monolayers. The results show a saturation adsorption frequency change of 6.8 kHz as opposed to 40 Hz for a commercial approximately 5-MHz sensor under identical loading conditions. From the analysis of the adsorption isotherm, the equilibrium adsorption constant of the adsorption of the protein layer was found to be K = 8.03 x 10(6) M(-1), which is in agreement with the values reported in the literature. The high sensitivity of the miniaturized QCM devices can be a significant advantage in both vapor and solution adsorption analyses.

This paper presents the results of electrochemical calibration experiments performed on micromachined quartz gravimetric sensors. The absolute mass sensitivity of bulk acoustic quartz crystal microbalance (QCM) can be improved into the sub-10-12 g range upon miniaturization of the resonator thickness and area. Using plasma etching, we have fabricated miniaturized QCMs with thicknesses of ~29 mum and diameters of 500 mum with f 0=58 MHz. Resonators with 60 nm thick Ti/Pt top electrodes were used to study the electrochemically induced oxide layer formation on the metal surface, the adsorption of hydrogen, and underpotential deposition (UPD) of Cu on Pt electrodes. The performance of microQCM is compared with the performance of a frequency matched overtone mode of a commercial 5 MHz resonator. Micromachined QCMs showed expected sensitivity improvement to UPD of Cu, however an unexpected hundred fold enhancement to oxygen and ~28 times enhancement in the sensitivity to hydrogen adsorption was observed which may be due to the roughness/porosity of the electrodes.

We report the fabrication and performance of a micromachined Y-cut quartz resonator based thermal infrared detector array. 1mm diameter and 18μm thick (90MHz) inverted mesa configuration quartz resonator arrays with excellent resonance characteristics have been fabricated by RIE etching of quartz. Temperature sensitivity of 7.2kHz/K was experimentally measured. Infrared calibration tests on the resonator array even without the use of infrared absorbers gave a responsivity of 14.3MHz/W and an NEP of 326nW. In this first report on the performance of the Y-cut quartz resonator infrared thermal detector array, the response time measurements were found to be limited by the slow measurement time of the impedance scans and the undesired heating of the quartz substrate. Most importantly, this initial work demonstrates the possibility of realizing infrared detector arrays for room temperature thermal imaging applications that can rival current state of the art in the field.