AT-cut Quartz Crystal Microbalance Research Articles

Machine learning approach to optimization of parameters for impedance measurements of Quartz Crystal Microbalance to improve limit of detection

Impedance spectroscopy allows real time monitoring of fundamental resonance frequency and harmonics of AT cut Quartz Crystal Microbalance (QCM) biosensors. Acquisition of accurate and high resolution spectroscopic data requires optimization of parameters, which is rarely performed as it requires an excessive number of experiments. In this work, machine learning clustering and classification algorithms are applied in an attempt to minimize the number of experiments by designating a small representative subset of chosen values of parameters, while preserving the variation of those values. Our results indicated it is possible to reduce the number of experiments required by more than 10 fold. The constructed model has both an unsupervised clustering part (k-means algorithm) and a supervised classification part (Support Vector Machine algorithm), working independently. From those two different approaches 83% compatibility is obtained. Such optimization can improve limit of detection (LOD) of glycerol concentrations by a factor of 12 using a QCM with a fundamental resonance frequency of 10 MHz. This approach can be applied not only to biosensors but also to chemical sensors involving resonance frequency monitoring by means of impedance spectroscopy, and has the potential to be expanded to systems with different transducer types, monitoring resonance by other means.

An Investigation of Factors Affecting Measurement Accuracy of Nanoparticles Real-time Sensor using Corona Discharge integrated with Quartz Crystal Microbalance

A nanoparticles real-time sensor in the present study was designed using corona discharge integrated with quartz crystal microbalance (QCM) or Nano-QCM detector. We investigated the following factors affecting the measurement accuracy of the detector; needle to plate distance, flow rate, and number of particles on QCM. DC high voltage power supply of 7 kV was used to maintain the positive corona voltages difference in the charger. The mass sensitivity of 10 MHz AT-cut QCMs coated by plate rigid gold film were investigated. The monodisperse aerosol particles smaller than 300 nm were initially used for the testing of the system. They were charged with negative corona voltages and then deposited on the surface of QCM electrode. Sauerbrey equation was used to describe the frequency-mass relationship at the QCM surface. Results show that the above factors significantly affect the accuracy of the detector measurement. The particles can be collected on a QCM electrode using the partial breakdown high voltage (reach to breakdown points) in terms of needle-to-plate corona discharge. The optimal needle-to-plate distance is 6 mm with maximum mass change (frequency shift) on QCM electrode of 0.607μg/min. The QCM collection efficiency of nanoparticles on the QCM electrode surface using corona discharge technique can be as high as 95% of total particles. Collection efficiency of PM0.1 is under investigation.

Uniformization of Mass Sensitivity Distribution of Silver Electrode QCM.

Quartz crystal microbalance (QCM) is a highly sensitive mass sensor and has been widely used in many fields. However, the nonuniform distribution of mass sensitivity will lead to poor reproducibility of QCM, which is not conducive to the application of QCM in some fields. Considering the effect of electrode shape, size, and material on mass sensitivity distribution, we found that for an AT-cut QCM with a fundamental frequency of 10 MHz, when the inner and outer diameters of silver ring electrode and the electrode loading factor are 2 and 5 mm and 0.0033, respectively, an approximately uniform mass sensitivity distribution can be obtained. The plating experiment in which rigid silver films were plated on the surface of electrode verified the uniformity. The uniform mass sensitivity distribution will make the application of QCM more convenient; the reproducibility can also be improved. This design of QCM will enrich QCM products and facilitate the application of QCM in various fields.

In Situ Acoustic Diagnostics of Particle-Binder Interactions in Battery Electrodes

Summary The high phase-transformation strain developed upon intercalation in the host particles of a composite battery electrode affects the polymeric binder network mechanically, deteriorating the electrode cycling performance. Here, electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D) is used to demonstrate a new strain-accommodation mechanism, in high-strain NaFePO 4 /PVdF electrodes, via relaxation of the binder network surrounding the intercalation particles. Complete mechanical degradation of the polymer network occurs during long-term cycling of NaFePO 4 electrodes in aqueous solutions (hard and tough behavior). In contrast, in aprotic solutions, a softened binder easily accommodates the high transformation strain, ensuring excellent electrode cycling performance (soft and tough behavior). Quantification of the high-frequency viscoelastic properties of an operating composite electrode linked to the binder's fracture toughness ensures fast and facile screening of the optimal polymeric binder/electrolyte solution combinations. This methodology should be extremely important for optimization of cycling performance of Li-Si anodes undergoing huge volume changes during cycling.

The temperature effect of AT-cut input quartz parameters on QCM effective properties calculated with equivalent circuit models

In what follows, AT-cut quartz crystal microbalance (QCM) effective properties for two commercial QCM substrates, are calculated as a function of temperature, while varying the degree of implementation regarding the temperature dependence of input quartz parameters in the transmission line (TL) model. Results for the effective quartz viscosity, oscillation area and external capacitance, are in qualitative agreement per property, irrespective of the implemented, input quartz parameter set for the calculations. However, the effective quartz thickness accounts for the quartz thermal expansion effect, only when quartz density is temperature adjusted, whereas quantitative deviations in the effective oscillation area, are qualitatively explained in the light of literature correlations, which relate the implemented input quartz parameter set, with inherent QCM energy dissipation metrics, and the magnitude of energy trapping. Moreover, the varying degree of input quartz parameter adjustment with temperature, yields qualitative and quantitative deviations from the expected response, in terms of a QCM quality metric, the C0/C1 ratio. Results suggest that the precision in the determination of the static capacitance C0 and the QCM effective properties incorporated therein, can be improved, with potential improvements in relevant, liquid or gas phase QCM applications.

PEDOT:PSS/QCM-based multimodal humidity and pressure sensor

A room temperature multimodal sensor composed of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) deposited on an AT-cut quartz crystal microbalance (QCM) crystal was fabricated. The sensor’s nonlinear motional resistance and frequency responses are deconvoluted using a feedforward backpropagation neural network (FBN), which allows a single sensor to function simultaneously as a relative humidity (RH) sensor and a pressure sensor using only two electrodes. We demonstrate that the predictive ability of the sensor is highly influenced by the data used to train the FBN. When training sets are tailored to resemble the operating conditions of the sensor, the sensor achieves an average resolution of <4% RH from 0 to 100% RH, even after H2O saturation occurs on the surface. Our results indicate that FBNs show strong promise for improving the resolution of low cost gas sensors and for expanding the range of environmental conditions in which a given sensor can operate.

Evaluation of the Specific Adsorption of Biotinylated Microbubbles Using a Quartz Crystal Microbalance

Specific adsorption of biotinylated microbubbles to streptavidin was evaluated by measuring the resonant frequency of an AT-cut quartz crystal microbalance (QCM). Streptavidin was fixed via self-assembled monolayers coated onto the QCM electrode. The resonant frequency of the QCM decreased as a result of specific adsorption of the biotinylated microbubbles, compared with the results for microbubbles containing no biotin. Additionally, there was significant evidence indicating that the frequency shift was caused by the internal gas of the microbubble, as well as the mass of the outer-shell material surrounding the gas. These results suggest that the QCM measurement system can be used effectively to evaluate the specific adsorption of targeted microbubbles.

Analysis and Improvement of the Mass Sensitivity for Piezoelectric Immunosensor

The objective of this study was to improve the low repeatability in quartz crystal microbalance (QCM) measurements. The constitutive equations for the thickness-shear vibrations of an AT-cut quartz crystal with surface electrodes were used to obtain the particle vibration displacement amplitude equation. Then the mass sensitivity of piezoelectric immunosensor was analyzed and the approach to improve low repeatability was proposed. A 10MHz modified-electrode AT-cut QCM with a maximum mass sensitivity of was designed to verify uniform mass sensitivity distribution in the fully electrode region. Analysis results show that in order to improve the accuracy in QCM immunosensor measurements, it is feasible to improve its mass sensitivity.

Demonstration of Molecular Sensing Using QCM Device Coated with Stimuli-sensitive Hydrogel

ABSTRACTMolecular sensing using stimuli-responsive viscoelastic property of amphiphilic polymer hydrogel was demonstrated. Thermo-responsive poly(N-isopropylacrylamide); NIPA, hydrogel immobilizing bovine serum albumin (BSA) in its polymer chain was synthesized on the AT-cut QCM (Quartz crystal microbalance). The device was provided to the sensing of anti-BSA antibody. The resonance behavior of QCM in response to the adsorption of anti-BSA antibody on the hydrogel was observed based on both the resonance frequency and resistance of QCM with impedance analysis. The QCM device coated with the LCST polymer hydrogel revealed a characteristic resonance behavior in response to the adsorption of anti-BSA antibody in the collapse phase of gel at which the gel lost most of its hydrated water. The resonance frequency and resistance in the collapsed gel were highly sensitive and their changes in response to the target adsorption were much larger than in the swelling state of gel. The use of the device at the LCST of NIPA gel is ideal because the largest amplification of the adsorption signal is available along with the largest phase change of NIPA gel.

New cut angle quartz crystal microbalance with low frequency–temperature coefficients in an aqueous phase

In a traditional quartz crystal microbalance (QCM), an AT-cut (cut angle φ = 35.25° in yxl orientation) quartz wafer is employed because it has low frequency–temperature coefficients (d F/d T) at room temperature region. But when a QCM is in contact with a liquid phase, its frequency is also related to the properties of the liquid, which are temperature dependent. The value of d F/d T is about 20 Hz/°C for a 9 MHz AT-cut QCM with one side facing water. In this work, a group of QCMs in new cut angles were prepared. The influence of the cut angle on the frequency–temperature characteristic, response sensitivities to surface mass loading and viscodensity of liquid were investigated. An intrinsically temperature-compensated QCM sensor that possesses low d F/d T values in aqueous solution was reported. When a 9 MHz QCM with φ = 35.65° was contacted with water with one side, its d F/d T value is close to zero at ca. 25 °C and its averaged value of |d F/d T| is only 0.6 Hz/°C in the temperature range of 23–27 °C. The frequency responses to surface mass loading and viscodensity of liquid phase are very close among the QCMs with the cut angles in the range of 35.15–35.7°. The intrinsically temperature-compensated QCM was applied to investigate the alternate adsorption processes of cationic polyelectrolyte and silica nanoparticle.

Frequency Behavior of a Quartz Crystal Microbalance (Qcm) in Contact with Selected Solutions

A device was constructed to monitor viscosity of solutions using fundamental frequency of 9 MHz and 10 MHz quartz crystal. Piezoelectric quartz crystals with gold electrodes were mounted by O-ring in between liquid flow cell. Only one side of the crystal was exposed to the solutions which were pumped through silicon tube by a peristaltic pump. The measured frequency shift was observed in order to investigate the interfacial behavior of some selected solution in contact with one surface of Quartz Crystal Microbalance (QCM). An analysis of the interaction between an AT-cut quartz crystal microbalance and various liquid system of analytical interest is presented. The analysis which includes piezoelectric effects and other influences; liquid properties, experimental conditions and the characteristic of the solution are reported. Oscillation in distilled water is taken as a reference. The frequency change caused by the density (ρ, gcm-3) and viscosity (η gcm-1s-1) were found to be proportional to the square root of the product, (ρ η). The result suggested that analysis of small frequency shifts during EQCM studies needs to account for changes in ρ and η of the solution. Generally, all the liquid tested showed an increment of the frequency shift with increasing content of solutes. For each solution, the frequency was recorded as the concentration increases from distilled water to a very concentrated solution. The frequency measurements carried out for saccharide solution produces the maximum changes of frequency shift compared with other solutions.

Rapid detection of bacterial spores using a quartz crystal microbalance (QCM) immunoassay

Weaponized spores of a pathogenic bacterium such as Bacillus anthracis are a new critical threat to mankind. The occurrences in New York and south Florida in 2001 showed the potential capability of the spores to be used for mass destruction. Due to their stealthiness during the infection and resistance to harsh environment, an early and prompt detection of the spores before they endanger the population is a significant issue. In this paper, we present a method of instant identification of Bacillus subtilis (nonpathogenic simulant for Bacillus anthracis) spores by constructing a dual quartz crystal microbalance (QCM) immunosensing system. A set of 10-MHz AT-cut QCMs operating in thickness shear mode are employed in an enclosed flowcell. Specificity is maintained through the use of an immuno-sensing layer consisting of monoclonal antibodies raised against spores of a single Bacillus species. The fidelity of sensing parameters is ensured by the presence of a reference device coated with an antibody that is not specific for the target antigen. Associating the QCM response signature with the specific binding of a particular species of Bacillus spore to an antibody has implications for future identification of pathogenic substances.

Quartz crystal microbalance with rigid mass partially attached on electrode surfaces

Quartz crystal microbalance (QCM) vibrating in thickness shear mode is used to detect the mass changes of the layer deposited on its surface. In this paper, an AT-cut quartz crystal microbalance with partial mass absorption on its electrode surface is modeled with Mindlin’s theory. The effect of position and percentage of covering area of the mass absorption is studied. The numerical simulation results show that QCM with larger electrode size is less sensitive to the percentage of covering area, and QCM with smaller electrode thickness is less sensitive to the position attachment of the mass absorption on its surface.

Detection of Two Orchid Viruses Using Quartz Crystal Microbalance-Based DNA Biosensors

ABSTRACT We have developed a piezoelectric DNA-sensor based on DNA-RNA hybridization for the detection of two orchid viruses, Cymbidium mosaic virus (CymMV) and Odontoglossum ringspot virus (ORSV). Specific oligonucleotide probes modified with a mercaptohexyl group at the 5'-phosphate end were directly immobilized onto 10-MHz AT-cut quartz crystal microbalance (QCM). QCMs coated with such oligonucleotide probes were exposed to test solutions containing viral RNA for hybridization. Various experimental conditions evaluated were (i) DNA probe coating concentration, (ii) sensitivity and specificity of the probes at different hybridization temperatures, and (iii) effects of incubation temperature on the hybridization time. The specific nucleotide probe-coated QCM-based DNA sensors were able to detect both CymMV and ORSV in quantities as low as approximately 1 ng in purified RNA preparations and 10 ng in the crude sap of infected orchids. This is the first application of a DNA biosensor for the detection of plant viruses.

Sialic Acid Imprinted Polymer-Coated Quartz Crystal Microbalance

Molecularly imprinted polymer-coated sensors for sialic acid were developed using a 9 MHz AT-cut quartz crystal microbalance (QCM). Recognition chips of the sensors used in this study were prepared by coating the two types of sialic acid-imprinted polymers with the use of p-vinylbenzeneboronic acid and/or N,N,N-trimethylaminoethyl methacrylate onto QCM. Each piezoelectric sensor showed a selective response to sialic acid and gave a linear relationship between frequency shift and amount of sialic acid from 20 to 250 nmol.

Sialic Acid Imprinted Polymer-Coated Quartz Crystal Microbalance

Molecularly imprinted polymer-coated sensors for sialic acid were developed using a 9 MHz AT-cut quartz crystal microbalance (QCM). Recognition chips of the sensors used in this study were prepared by coating the two types of sialic acid-imprinted polymers with the use of p-vinylbenzeneboronic acid and/or N,N,N-trimethylaminoethyl methacrylate onto QCM. Each piezoelectric sensor showed a selective response to sialic acid and gave a linear relationship between frequency shift and amount of sialic acid from 20 to 250 nmol.

Molecularly Imprinted Polymer-Coated Quartz Crystal Microbalance for Detection of Biological Hormone

A piezoelectric sensor with a molecularly imprinted synthetic polymer receptor was developed. A plant hormone, indole-3-acetic acid (IAA) was used as the model target molecule, and an IAA-imprinted polymer was coated onto a 9 MHz AT-cut quartz crystal microbalance. The sensor showed a selective response and gave a linear relationship between frequency shift and amount of IAA in the range from 10 to 200 nmol.

Quartz crystal microbalance: A new design eliminates sensitivity outside the electrodes, often wrongly attributed to the electric fringing field

Sensitivity outside the electrodes of a quartz crystal microbalance (QCM) is typically 5%–10% of the total sensitivity for the popular planar AT-cut type, and can be a problem in many types of adsorption measurement. This off-electrode sensitivity has sometimes been assumed incorrectly to be due mainly to the electric “fringing field” at the electrode edge, despite the fact that no quantitative theory has been put forward as to how the fringing field could lead to off-electrode sensitivity. In fact, off-electrode sensitivity results from the mass distribution of the electrodes, and is virtually independent of the electric field. Recognition of this fact leads directly to a new QCM design which virtually eliminates the problem altogether; in the new design sensitivity outside the electrode covered area has been reduced from 6% to about 0.3%. Equations previously derived to predict the differential mass sensitivity of existing planar AT-cut QCM sensors are applied to the new design, and compared to experimental calibration measurements obtained using the ink-dot method. Agreement with theory is excellent.

Gas-phase molecular recognition on functional monolayers immobilized on a highly sensitive quartz-crystal microbalance

Self-assembled monolayers of alkanethiols having functional groups (HS-(CH 2) 10-X X = -H, -COOH, -CONH 2, -NH 2, thymine and adenine bases) were immobilized on the Au electrode of a quartz-crystal microbalance (QCM), and binding kinetics of guest molecules from the gas phase were studied from time courses of frequency decreases (mass increases) of the QCM. A highly sensitive, 63-MHz overtone frequency of a conventional 9-MHz at AT-cut QCM was developed to detect monolayer adsorption of small molecules. When acetic acid was employed as guest molecules, it adsorbed onto the -CONH 2 membrane as a Langmuir-type monolayer and adsorbed as multilayers onto the -COOH and -NH 2 membranes, but hardly adsorbed onto the simple alkane membrane (-H membrane). When self-assembled monolayers bearing a thymine or adenine base as a terminal group were employed, selective binding processes of complementary guest molecules were observed: 2-aminopyridine (an adenine model) and γ-butyrolactam (a thymine model) selectively bound to the thyamine and adenine monolayers, respectively.

Guest selective adsorption from the gas phase onto a functional self-assembled monolayer immobilized on a super-sensitive quartz-crystal microbalance

A self-assembled monolayer of alkanethiols having functional groups ( HS-(CH 2) 10− X; X = −H, −COOH, −CONH 2 ) was immobilized on Au electrodes of a quartz-crystal microbalance (QCM), and the adsorption behavior of gaseous organic molecules, such as aliphatic acids, amines, alcohols, and alkanes, was observed from frequency decreases (mass increases) of the QCM plate in gas-phase. We used a super-sensitive, seventh overtone frequency of a 9 MHz AT-cut QCM (63 MHz) in order to detect a monolayer adsorption of small organic molecules. Association constant ( K a ), adsorption ( K 1), and desorption rate constants ( K −1) could be obtained from curve fitting of time courses of frequency changes (mass changes). All organic molecules hardly adsorbed onto the alkane ( X = − H) membrane. To the -CONH 2 membrane, only acetic acid can be selectively adsorbed compared with the -H membrane, but not caproic and nonanoic acids, which explains that hydrogen-bond interactions are important but hydrophobic interactions are not. To the -COOH membrane, both acetic acid and ethyle-nediamine can largely adsorb compared with the -H membrane, but not monoamines. The adsorption of ethylenediamine can be explained by acid-base interactions.