Resonant Frequency Of Quartz Crystal Microbalance Research Articles

Quantification of Particle Filtration Using a Quartz Crystal Microbalance Embedded in a Microfluidic Channel.

To quantify colloidal filtration, a quartz crystal microbalance (QCM) with a silicon dioxide surface is embedded on the inner surface of a microfluidic channel to monitor the real-time particle deposition. Potassium chloride solution with micrometer-size polystyrene particles simulating bacterial strains flows down the channel. In the presence of intrinsic Derjaguin-Landau-Verwey-Overbeek (DLVO) intersurface forces, particles are trapped by the quartz surfaces, and the increased mass shifts the QCM resonance frequency. The method provides an alternative way to measure filtration efficiency in an optically opaque channel and its dependence on the ionic concentration.

Rapid Whole Blood Clot Retraction Assay on Quartz Crystal Microbalance

This letter demonstrates, for the first time, a novel, rapid automated whole blood clot retraction assay utilizing quartz crystal microbalance resonant frequency monitoring. Tissue factor is selected to initiate coagulation. The test turnaround time is 10–20 min, during which a real-time coagulation trace is recorded in parallel with a reference coagulation trace. The reference sample is the same blood sample that is treated by platelet aggregation inhibitor, and the difference between the two traces indicates the quantitative platelet effect on clotting. This differential approach enables determination of a hematocrit-independent parameter characterizing the intensity of clot retraction. In the case of samples with normal hemostatic characteristics, the intensity of retraction is a linear function of platelet count, whereas the retraction is reduced in the case of platelet hypofunction. Moreover, in combination with a clotting time parameter derived from the same coagulation trace, the method allows primary differentiation between three groups of bleeding disorders of various etiology, including platelet disorders, defects in plasma factors, and hypofibrinogenaemia.

Intelligent Mobile Electronic Nose System Comprising a Hybrid Polymer-Functionalized Quartz Crystal Microbalance Sensor Array.

We devised a low-cost mobile electronic nose (e-nose) system using a quartz crystal microbalance (QCM) sensor array functionalized with various polymer-based thin active films (i.e., polyacrylonitrile, poly(vinylidene fluoride), poly(vinyl pyrrolidone), and poly(vinyl acetate)). It works based on the gravimetric detection principle, where the additional mass of the adsorbed molecules on the polymer surface can induce QCM resonance frequency shifts. To collect and process the obtained sensing data sets, a multichannel data acquisition (DAQ) circuitry was developed and calibrated using a function generator resulting in a device frequency resolution of 0.5 Hz. Four prepared QCM sensors demonstrated various sensitivity levels with high reproducibility and consistency under exposure to seven different volatile organic compounds (VOCs). Moreover, two types of machine learning algorithms (i.e., linear discriminant analysis and support vector machine models) were employed to differentiate and classify those tested analytes, in which classification accuracies of up to 98 and 99% could be obtained, respectively. This high-performance e-nose system is expected to be used as a versatile sensing platform for performing reliable qualitative and quantitative analyses in complex gaseous mixtures containing numerous VOCs for early disease diagnosis and environmental quality monitoring.

Improvement QCM Quality By Polystyrene Coating and Bovine Serum Albumin as Immobilization Agent

Polystyrene (PS) thin film with various concentration of mass (1%, 3%, and 5%) has been deposited onto Quartz Crystal Microbalance (QCM) surface by a spin coating method. The purpose of this research is the improvement of Bovine Serum Albumin (BSA) immobilization into the QCM surface. The QCM resonance frequency has been investigated by means of Impedance Analyzer. The film thickness was calculated by the Sauerbrey equation. The surface roughness of the PS layer was observed by noncontact Topography Measuring System (TMS-1200). Calculation result using a Sauerbrey equation shows the thickness of the PS layer increases with the increasing PS concentration. The QCM/PS with 1% and 5% concentration of mass has rougher morphology and more frequency shifts caused by BSA injection compared to 3% concentration of PS.

Strategic Approaches for Highly Selective and Sensitive Detection of Hg2+ Ion Using Mass Sensitive Sensors.

Here we present a quartz crystal microbalance (QCM) sensor for the highly selective and sensitive detection of Hg2+ ion, a toxic chemical species and a hazardous environmental contaminant. Hg2+ ion can be quantitatively measured based on changes in the resonance frequency of QCM following mass changes on the QCM sensor surface. The high selectivity for Hg2+ ion in this study can be obtained using a thymine-Hg2+-thymine pair, which is more stable than the adenine-thymine base pair in DNA. On the other hand, gold nanoparticles (AuNPs) and their size-enhancement techniques were used to amplify the QCM signals to increase the sensitivity for Hg2+ ion. With this strategic approach, the proposed QCM sensor can be used to quantitatively analyze Hg2+ ion with high selectivity and sensitivity. The detection limit was as low as 98.7 pM. The sensor failed to work with other metal ions at concentrations 1000-times higher than that of the Hg2+ ion. Finally, the recovery does not exceed 10% of the original value for the detection of Hg2+ ion in tap and bottled water. The results indicate acceptable accuracy and precision for practical applications.

QCM-Micropillar-Based Coupled Resonators in the Detection of Gas Mass Flow Rates

We report the discovery of a micropillar-based quartz crystal microbalance (QCM) coupled resonator sensor (CRS) in detecting flow rates of gases with different densities. The fabricated QCM CRS was housed in a stainless steel chamber and the resonance frequency changes associated with gas flow at small values of mass flow rates inside the chamber were measured. Argon and helium were used as the test gases. The results obtained revealed an extraordinary sensitivity to mass flow rate changes under room temperature and flow rates as low as 20 sccm. Moreover, the QCM-CRS system was able to differentiate the densities of the two gases. Identical experiments conducted using a bare QCM showed that the mass flow rates had negligible effects on the QCM resonance frequency response. Thus, it is evident that a coupled resonance phenomenon plays a significant role in enabling the QCM to be sensitive to small mass changes caused by differences in flow rates. We propose that the QCM-CRS system can be used as a new class of mass flow sensing element, especially for flow measurement in vacuum processing systems.

Controlled Deposition Number of Organic Molecules Using Quartz Crystal Microbalance Evaluated by Scanning Tunneling Microscopy Single-Molecule-Counting.

Precise control of organic molecule deposition on a substrate is quite important for fabricating single-molecule-based devices. In this study, we demonstrate whether a quartz-crystal microbalance (QCM) widely used for a film growth calibration has the ability to precisely measure the number of organic molecules adsorbed on a substrate. The well-known Sauerbrey's equation is extended to formulate the relation between QCM resonant frequency shift and the number of adsorbed molecules onto the QCM surface. The formula is examined by QCM measurements of sublimation of π-conjugated organic molecules and direct counting of the deposited molecules one by one onto metal substrates, using ultrahigh vacuum low-temperature scanning tunneling microscopy (STM). It is revealed that the number of adsorbed molecules evaluated by QCM ( NQCM) show good agreement with those counted from the STM images ( NSTM) within the error of ±25%. The results ensure the QCM capability for controlling the deposition number of organic molecules with high accuracy, that is, if one needs to deposit 100 molecules on the substrate, QCM control promises deposition of 100 ± 25 molecules.

A quartz crystal microbalance-based biosensor for enzymatic detection of hemoglobin A1c in whole blood

Abstract Here we present a quartz crystal microbalance (QCM) biosensor for enzymatic detection of hemoglobin A1c (HbA1c). It shows average plasma glucose concentration readings over the prior three months. HbA1c can be quantitatively measured based on changes of resonance frequency of QCM following mass changes on QCM sensor surface. These mass changes were caused by size enlargement of conjugated gold nanoparticle with thiol-terminated SAMs on the sensor surface due to gold staining by hydrogen peroxide (H2O2) generated from enzymatic HbA1c assay. Finally, we investigated sensor responses due to mass changes on various concentrations of applied H2O2. We also demonstrated its capability for analyzing HbA1c in whole blood sample with enzymatic assay. Our results showed that the proposed QCM biosensor could quantitatively analyze HbA1c with a detection limit of 0.147% HbA1c with respect to hemoglobin and a coefficient variation of less than 10%.

Hybrid localized surface plasmon resonance and quartz crystal microbalance sensor for label free biosensing

We report on the design and fabrication of a hybrid sensor that integrates transmission-mode localized surface plasmonic resonance (LSPR) into a quartz crystal microbalance (QCM) for studying biochemical surface reactions. The coupling of LSPR nanostructures and a QCM allows optical spectra and QCM resonant frequency shifts to be recorded simultaneously and analyzed in real time for a given surface adsorption process. This integration simplifies the conventional combination of SPR and QCM and has the potential to be miniaturized for application in point-of-care (POC) diagnostics. The influence of antibody-antigen recognition effect on both the QCM and LSPR has been analyzed and discussed.

Round-patterned ZnO nanostructure coated with siloxane-based polymer for nerve agent detection

The alignment of zinc oxide (ZnO) nanostructures is expected to improve device sensitivities due to large surface areas which can be utilized to capture significant quantities of gas particles. In this study, we investigated patterned ZnO nanorods modified with polystyrene monolayers synthesized directly onto a quartz crystal microbalance (QCM) cell to increase the coating surface area of the sensing material. Also, we designed and synthesized a siloxane-based polymer (S1 polymer) as a sensing material. The patterned ZnO nanorods coated with S1 polymers were fabricated and used for the detection of dimethyl methylphosphonate (DMMP). The resonance frequency of QCM was shifted due to the adsorption and desorption of a compound at the surface of the modified electrodes. We have synthesized an S1 polymer that exhibited high sensitivity to DMMP. The patterned ZnO nanorods coated with the polymer also exhibited improved sensitivity due to an enhanced surface area capable of adsorbing more DMMP vapor.

QCM Coupled Resonating Systems Under Vacuum: Sensitivity and Characteristics

We present the underlying physics in the resonance frequency characteristics of a bare quartz crystal microbalance (QCM) and a QCM-micro pillar based coupled resonator sensor (QCM-CRS) when they were subjected to pressure changes in a vacuum chamber. The QCMs experienced an increase in resonance frequency with decrease in pressure due to an inverse mass loading effect introduced on the QCM surface. However, when the pressure (below atmospheric pressure) dominated the mass loading, the resonance frequency of QCMs decreased. A sensitivity increase of 11 times to the pressure changes was observed for the case of QCM-CRS made of resonating micropillars attached around the central region of the electrode. In addition, the resonance frequency shift was linear for pressure changes between 31 and 71 kPa, demonstrating the possibility of employing the QCM-CRS as a vacuum detector element. The proposed sensor element is envisioned to have wide industrial applications ranging from detecting vacuum in chambers used in coating systems to crack detection in closed chambers.

Microfluidic quartz-crystal-microbalance (QCM) sensors with specialized immunoassays for extended measurement range and improved reusability

Quartz crystal microbalances (QCM) are well known mass sensitive devices. By combining them with specialized antibodies, sensitive biosensors with detection limits down to some nanogram of substance can be obtained. While the antibody coating determines which substances will be detected, the QCM's limit of detection is determined by the required minimal mass change. Therefore, measurements of biological samples containing small target molecules at low concentrations remain challenging. Here, we present the fabrication of disposable but also regenerative QCM devices with microfluidic housing and an approach to improve the detection limit of a QCM by employing an additional, heavier molecule to increase the total added apparent mass, leading to a larger drop of the QCMs resonant frequency per amount of measured substance. As any signal amplification bears the risk to lose its benefit by amplification of unspecific binding too, we further developed an in vitro designed antibody sandwich pair, offering more specific target molecule (CRP) detection and only temporary binding which renders the device reusable within minutes. No additional chemicals or regeneration protocols between measurements are necessary, sole purging with buffer solution is sufficient. To achieve signal amplification, streptavidin was attached via biotin to the second antibody. The resulting frequency drop was up to five times higher compared to the original antibody sandwich. In the absence of CRP, no resonant frequency change rising above signal noise could be observed in presence of the second antibody and streptavidin. The presented concept is broadly expandable. The use of even heavier molecules or nanoparticles for mass amplification should allow higher frequency shifts per amount of target substance and promises to extend the measurement range of QCMs into the sub-nanogramm region.

Area density of streptavidin can be evaluated by the number density of biotinylated microbubbles

Targeted microbubbles (TMBs) that specifically accumulate on target sites via biochemical bonds have been studied for using ultrasound diagnoses and therapies (e.g., ultrasound molecular imaging) in the research field. To understand the specific interactions between TMBs and their target molecules, a biosensor system with a quartz crystal microbalance (QCM) was constructed. In this system, TMBs become absorbed on their target molecule, which was fixed to the QCM surface via a self-assembled monolayer. Our previous studies showed that the system allowed the evaluation of the interaction between biotinylated MBs and the target molecule, streptavidin, by monitoring changes in the resonant frequency of QCM [Muramoto et al., Ultrasound Med. Biol., 40(5), 1027–1033 (2014)]. This paper investigates how the amount of streptavidin relates to the amount of absorbed biotinylated MBs. The amount of streptavidin on the QCM surface was evaluated by measuring the difference in its resonant frequency before and after the fixation of streptavidin. After which, the amount of absorbed MBs was also evaluated by measuring the frequency shift during the interaction between MBs and the target molecule. Our results showed a weak correlation between the amounts of bound MB and the density of streptavidin (correlation coefficient, r = 0.44), suggesting that the area density of target molecule can be evaluated by estimating the number density of TMBs.

Resonant characteristics and sensitivity dependency on the contact surface in QCM-micropillar-based system of coupled resonator sensors

We report the characteristics and sensitivity dependence over the contact surface in coupled resonating sensors (CRSs) made of high aspect ratio resonant micropillars attached to a quartz crystal microbalance (QCM). Through experiments and simulation, we observed that when the pillars of resonant heights were placed in maximum displacement regions the resonance frequency of the QCM increased following the coupled resonance characteristics, as the pillar offered elastic loading to the QCM surface. However, the same pillars when placed in relatively lower displacement regions, in spite of their resonant dimension, offered inertial loading and resulted in a decrease in QCM resonance frequency, as the displacement amplitude was insufficient to couple the vibrations from the QCM to the pillars. Accordingly, we discovered that the coupled resonance characteristics not only depend on the resonant structure dimensions but also on the contact regions in the acoustic device. Further analysis revealed that acoustic pressure at the contact surface also influences the resonance frequency characteristics and sensitivity of the CRS. To demonstrate the significance of the present finding for sensing applications, humidity sensing is considered as the example measurand. When a sensing medium made of resonant SU-8 pillars was placed in a maximum displacement region on a QCM surface, the sensitivity increased by 14 times in comparison to a resonant sensing medium placed in a lower displacement region of a QCM surface.

Mineral magnetite as precursor in the synthesis of multi-walled carbon nanotubes and their capabilities of hydrogen adsorption

Mineral magnetite was used as metallic oxide catalysts in the synthesis of Multi-Walled Carbon Nanotubes (MWCNTs) by Aerosol Assisted Chemical Vapor Deposition (AACVD). The structural and morphological information of MWCNTs was obtained by X-ray Diffraction (XRD), Raman Spectroscopy (RS), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). The hydrogen storage capacity and the gas adsorption kinetics of the MWCNTs exposed to H2 at different pressures were determined using a quartz crystal microbalance (QCM). It was found that the hydrogen adsorption capacity was strongly dependent on the chemical, structural and morphological characteristics of the MWCNTs which, in turn, depend on the proportion of the starting materials (mineral magnetite and zeolite) used for the synthesis by AACVD. However, no a clear correlation was found between each one of these characteristics and the adsorption properties since the sample was affected by gas exposure during the H2 loading/unloading cycles. The maximum adsorption capacity was 1.76 wt% at 44 Torr of H2 exposure pressure. The adsorption kinetics was determined by in situ monitoring the QCM resonance frequency. As expected, a faster H2 adsorption kinetics of the MWCNTs occurred when the sample was exposed to higher H2 pressures. In general, there are measurable H2 adsorption between 60 s and 100 s before reaching saturation.

Direct measurement of the amount of dissociated hydrogen atoms attached on graphene

Recently, we reported n-type graphene can be achieved simply using H2 molecules. It was understood by the attachment of hydrogen atoms dissociated on the surface of graphene. However, the amount of attached hydrogen has not been yet investigated. Here, we show the possibility of the formation of CH bonds due to the H2 exposure theoretically and the mass of the attached hydrogen atoms on graphene experimentally. The amount of the attached hydrogen atoms has been measured by a quartz crystal microbalance (QCM). After exposure of a multilayer graphene (MLG) to 20bar of H2 pressure at 353K for 20h, the resonance frequency (RF) of QCM decreased. It indicates that the mass of the MLG increases. On the basis of the RF variation, we concluded that the hydrogen atoms were bonded to 3.84% of carbon atoms in the MLG. In order to confirm the CH bonding of MLG, Raman spectroscopy was performed before and after exposure to H2 pressure. On exposure, the D peak developed and the peak for 2-D graphite in 2D band increased. The experimental results and theoretical calculation demonstrate that the H2 molecules on the surface of the graphene are dissociated and that some of dissociated H atoms are attached on graphene.

Modelling of blood component flexibility using quartz crystal microbalance

Quartz crystal microbalance (QCM) is a sensitive technique for real-time monitoring of cell adsorption, aggregation and cell-to-surface interaction processes. However, cell adhesion time courses are usually considered as merely qualitative, being presented in terms of QCM resonant frequency shift and/or changes in the dissipation parameter, the precise physical meanings of which are not derived. In the present study, a model of cell adhesion to the QCM sensor surface was proposed. The main output parameter of the model is the rigid mass density, Mr, being related to QCM resonant frequency and dissipation with a simple expression. From this, it can be determined that Mr is the mass density of the layer formed by all directly adhered parts of the cell, being rigidly coupled to the sensor surface. We postulate that the Mr(t) value is proportional to the number of cells adhered by the time t, and that the coefficient of this proportionality is strongly dependent on cell-to-surface interaction forces.

Microgel-based etalon coated quartz crystal microbalances for detecting solution pH: The effect of Au overlayer thickness

Poly (N-isopropylacrylamide)-co-acrylic acid (pNIPAm-co-AAc) microgels were “painted” on the Au electrode of a quartz crystal microbalance (QCM). Another Au layer (overlayer) was subsequently deposited on the microgel layer. This structure is known as a microgel-based etalon. These devices have been shown to exhibit optical properties (i.e., color) that depend on solution pH and temperature, among other things. Previously, we measured QCM frequency shifts that are a result of solution pH changes; the frequency shifts are a direct result of the pH dependent solvation state of the microgels that make up the etalon. In fact, the shifts observed for the etalons were much greater in magnitude than just a microgel layer immobilized on the QCM crystal without the Au overlayer. We reasoned that the Au overlayer lead to an enhancement of the observed frequency change due to its mass. In this submission we investigate how the Au overlayer thickness (mass) affects the observed sensitivity to solution pH. We found that the change in QCM resonant frequency depended dramatically on the mass of the Au overlayer.

Acoustic interference suppression of quartz crystal microbalance sensor arrays utilizing phononic crystals

Acoustic interference suppression of quartz crystal microbalance (QCM) sensor arrays utilizing phononic crystals is investigated in this paper. A square-lattice phononic crystal structure is designed to have a complete band gap covering the QCM's resonance frequency. The monolithic sensor array consisting of two QCMs separated by phononic crystals is fabricated by micromachining processes. As a result, 12 rows of phononic crystals with band gap boost insertion loss between the two QCMs by 20 dB and also reduce spurious modes. Accordingly, the phononic crystal is verified to be capable of suppressing the acoustic interference between adjacent QCMs in a sensor array.

Integration of Quartz Crystal Microbalance with Vibrational Sum Frequency Spectroscopy–Quantification of the Initial Oxidation of Alkanethiol-Covered Copper

We report the first integration of the interface sensitive technique vibrational sum frequency spectroscopy (VSFS) and the mass sensitive technique quartz crystal microbalance (QCM). VSFS-QCM has been applied in-situ to follow the formation of a thin Cu2O-like oxide on octadecanethiol-covered copper in dry air at ambient pressure conditions. We observed significant changes and an evolution of the VSF spectra caused by alterations in the electronic properties of the metal surface, and simultaneous shifts in the QCM resonance frequency due to a mass change during the formation of the oxide. QCM and VSFS exhibit a resolution corresponding to the formation of around 2% and 5% of an ideal monolayer of Cu2O, respectively. The successful integration of QCM increases the versatility of VSFS in numerous applications, where simultaneous in situ mass and spectroscopic information is desirable.