Piezoelectric Quartz Crystal Research Articles

Chemometric differentiation of coffee varieties using gas sensors based on polymer-modified piezoelectric quartz crystals

Chemometric differentiation of coffee varieties using gas sensors based on polymer-modified piezoelectric quartz crystals

Sensing of halogenated aromatic hydrocarbons in water with a cavitand coated piezoelectric device

A study leading to the development of a piezoelectric sensing device for environmental monitoring of aromatic micropollutants in water is reported. A Piezoelectric Quartz Crystal (PQC) was functionalized through electropolymerization of a quinoxaline cavitand, known to possess remarkable capabilities in selectively trapping aromatic compounds through multiple π-π and CH-π interactions. The obtained film was characterized via X-ray Photoelectron spectroscopy (XPS) to elucidate its chemical composition. The design and synthesis of the new quinoxaline cavitand functionalized at the upper rim with a bithiophene moiety suitable for electropolymerization is described. The molecular structure of the new receptor was elucidated via X-ray diffraction analysis. The performance of the obtained sensor towards selected chlorinated and not chlorinated hydrocarbons in water was tested. Excellent limit of detection (0.17 ppm), below the present stringent Italian value, was achieved for 1,2,4-trichlorobenzene, outperforming conventional systems. The frequencymetric sensor showed high reproducibility from independent functionalized PQCs, with RSD values lower than 5%.

A GOQD modified IDE-PQC humidity sensor based on impedance-frequency tuning principle with enhanced sensitivity

In this work, a graphene oxide quantum dots (GOQD) modified IDE-PQC humidity sensor based on the impedance-frequency tuning principle is presented. The proposed sensor consists of an electrically exposed interdigital electrode, which is modified with a GOQD film, connected in series with a piezoelectric quartz crystal. To explain the working principle of the proposed sensor, a contrastive GOQD modified IDE-PQC sensor with a thin insulating layer on the IDE is used in the comparison test. The experimental results showed that the proposed sensor had a high sensitivity of up to 81 Hz/(% RH), and it was ten times more sensitive than the contrastive sensor. It was demonstrated that the proposed sensor was sensitive to both permittivity and conductivity changes of the GOQD sensing film caused by humidity variations while the contrastive sensor could respond only to the dielectric permittivity change. This work introduces a feasible way to construct a digital humidity sensor with high sensitivity.

Cheeses Made from Raw and Pasteurized Cow's Milk Analysed by an Electronic Nose and an Electronic Tongue.

Cheese prepared from whole milk, raw and pasteurized, were analysed by an electronic nose based on piezoelectric quartz crystals and an electronic tongue based on potentiometric sensors, immediately after their preparation and along ripening (after 7 and 21 days). Whey was also analysed by the potentiometric electronic tongue. Results obtained by the electronic nose and tongue were found to be complementary, with the electronic nose being more sensitive to differences in the milk and the electronic tongue being more sensitive to milk pasteurization. Electronic tongue was able to distinguish cheeses made from raw and pasteurized milk, both analysing the whey or the curd, with correct classification rate of 96% and 84%, respectively. Besides, the electronic nose was more sensitive than the electronic tongue to the ripening process, with large differences between samples after 7 and 21 days, while the electronic tongue was only sensitive to the initial maturation stages, with large difference between freshly prepared cheese and with seven days of maturation.

Electrode configuration and electrical dissipation of mechanical energy in quartz crystal resonators

Mechanical resonators made with monolithic piezoelectric quartz crystals are promising for studying new physical phenomena. High mechanical quality factors (Q) exhibited by the mm-sized quartz resonators make them ideal for studying weak couplings or long timescales in the quantum regime. However, energy losses through mechanical supports pose a serious limiting factor for obtaining high quality factors. Here we investigate how the Q of quartz resonators at deep cryogenic temperatures can be limited by several types of losses related to anchoring. We first introduce means to reduce the mechanical losses by more than an order of magnitude in a no-clamping scheme, obtaining Q-factors of 108 of the lowest shear mode. We can exclude a wide coverage of aluminum metalization on the disk or bond wires as sources of dissipation. However, we find a dramatic reduction of the Q-factor accompanying an electrode configuration that involves strong focusing of the vibrations in the disk center. We propose a circuit model that accounts for the reduced mechanical Q-factor in terms of electrical losses. In particular, we show how the limiting factor for losses can be small ohmic dissipation in a grounding connection, which can be interpreted as electrical anchor losses of the mechanical device.

Impedance method for measuring shear elasticity of liquids

Experimental results of studying low-frequency (74 kHz) shear elasticity of polymer liquids by the impedance method (analogous to the Mason method) are presented. A free-volume thick liquid layer is placed on the horizontal surface of a piezoelectric quartz crystal with dimensions 34.7 × 12 × 5.5 cm. The latter performs tangential vibrations at resonance frequency. The liquid layer experiences shear strain, and shear waves should propagate in it. From the theory of the method, it follows that, with an increase in the layer thickness, both real and imaginary resonance frequency shifts should exhibit damped oscillations and tend to limiting values. For the liquids under study, the imaginary frequency shift far exceeds the real one, which testifies to the presence of bulk shear elasticity.

Selection of a new Mycobacterium tuberculosis H37Rv aptamer and its application in the construction of a SWCNT/aptamer/Au-IDE MSPQC H37Rv sensor

A rapid and accurate detection method for Mycobacterium tuberculosis (M. tuberculosis) is essential for effectively treating tuberculosis. However, current detection methods cannot meet these clinical requirements because the methods are slow or of low specificity. Consequently, a new highly specific ssDNA aptamer against M. tuberculosis reference strain H37Rv was selected by using the whole-cell systematic evolution of ligands by exponential enrichment technique. The selected aptamer was used to construct a fast and highly specific H37Rv sensor. The probe was produced by immobilizing thiol-modified aptamer on an Au interdigital electrode (Au-IDE) of a multichannel series piezoelectric quartz crystal (MSPQC) through Au-S bonding, and then single-walled carbon nanotubes (SWCNTs) were bonded on the aptamer by π-π stacking. SWCNTs were used as a signal indicator because of their considerable difference in conductivity compared with H37Rv. When H37Rv is present, it replaces the SWCNTs because it binds to the aptamer much more strongly than SWCNTs do. The replacement of SWCNTs by H37Rv resulted in a large change in the electrical properties, and this change was detected by the MSPQC. The proposed sensor is highly selective and can distinguish H37Rv from Mycobacterium smegmatis (M. smegmatis) and Bacillus Calmette-Guerin vaccine (BCG). The detection time was 70min and the detection limit was 100cfu/mL. Compared with conventional methods, this new SWCNT/aptamer/Au-IDE MSPQC H37Rv sensor was specific, rapid, and sensitive, and it holds great potential for the early detection of H37Rv in clinical diagnosis.

A novel method for the rapid detection of microbes in blood using pleurocidin antimicrobial peptide functionalized piezoelectric sensor

The rapid detection of microbes is critical in clinical diagnosis and food safety. Culture-dependent assays are the most widely used microbial detection methods, but these assays are time-consuming. In this study, a rapid microbial detection method was proposed using a pleurocidin/single-walled carbon nanotubes/interdigital electrode-multichannel series piezoelectric quartz crystal (pleurocidin/SWCNT/IDE-MSPQC) sensor. The selected pleurocidin antimicrobial peptide served as a recognition probe that exhibits broad-spectrum antimicrobial activity and the SWCNT acted as the electronic transducer and cross-linker for the immobilization of pleurocidin on the IDE. The response mechanism of the sensor was based on the specific interaction between pleurocidin and the microbe causing pleurocidin to detach from the SWCNT modified IDE, resulting in a sensitive frequency shift response of the MSPQC. Microbes that may be clinically present in the bloodstream during an infection were successfully detected by the proposed method within 15min. The developed strategy provides a new universal platform for the rapid detection of microbes.

A 3D CFD Simulation and Analysis of Flow-Induced Forces on Polymer Piezoelectric Sensors in a Chinese Liquors Identification E-Nose.

Chinese liquors can be classified according to their flavor types. Accurate identification of Chinese liquor flavors is not always possible through professional sommeliers’ subjective assessment. A novel polymer piezoelectric sensor electric nose (e-nose) can be applied to distinguish Chinese liquors because of its excellent ability in imitating human senses by using sensor arrays and pattern recognition systems. The sensor, based on the quartz crystal microbalance (QCM) principle is comprised of a quartz piezoelectric crystal plate sandwiched between two specific gas-sensitive polymer coatings. Chinese liquors are identified by obtaining the resonance frequency value changes of each sensor using the e-nose. However, the QCM principle failed to completely account for a particular phenomenon: we found that the resonance frequency values fluctuated in the stable state. For better understanding the phenomenon, a 3D Computational Fluid Dynamics (CFD) simulation using the finite volume method is employed to study the influence of the flow-induced forces to the resonance frequency fluctuation of each sensor in the sensor box. A dedicated procedure was developed for modeling the flow of volatile gas from Chinese liquors in a realistic scenario to give reasonably good results with fair accuracy. The flow-induced forces on the sensors are displayed from the perspective of their spatial-temporal and probability density distributions. To evaluate the influence of the fluctuation of the flow-induced forces on each sensor and ensure the serviceability of the e-nose, the standard deviation of resonance frequency value (SDF) and the standard deviation of resultant forces (SDFy) in y-direction (Fy) are compared. Results show that the fluctuations of Fy are bound up with the resonance frequency values fluctuations. To ensure that the sensor's resonance frequency values are steady and only fluctuate slightly, in order to improve the identification accuracy of Chinese liquors using the e-nose, the sensors in the sensor box should be in the proper place, i.e., where the fluctuations of the flow-induced forces is relatively small. This plays a significant reference role in determining the optimum design of the e-nose for accurately identifying Chinese liquors.

Calcium-induced calmodulin conformational change. Electrochemical evaluation

Calmodulin (CaM) is an essential protein present in all eukaryote cells, ranging from vertebrates to unicellular organisms. CaM is the most important Ca2+ signalling protein, composed of two domains, N- and C-terminal domains, linked by a flexible central α-helix, and is responsible for the regulation of numerous calcium-mediated signalling pathways. Four calcium ions bind to CaM, changing its conformation and determining how it recognizes and regulates its cellular targets. The oxidation mechanism of native and denatured CaM, at a glassy carbon electrode, was investigated using differential pulse voltammetry and electrochemical impedance spectroscopy. Native and denatured CaM presented only one oxidation peak, related to the tyrosine amino acid residue oxidation. Calcium-induced calmodulin conformational change and the influence of Ca2+ concentration on the electrochemical behaviour of CaM were evaluated, and significant differences, in the tyrosine amino acid residue peak potential and current, in the absence and in the presence of calcium ions, were observed. Gravimetric measurements were performed with a graphite coated piezoelectric quartz crystal with adsorbed CaM, and calcium aggregation by CaM was demonstrated.

Determination of 5-hydroxymethylfurfural in honey, using headspace-solid-phase microextraction coupled with a polyoxometalate-coated piezoelectric quartz crystal.

High concentrations of 5-hydroxymethylfurfural (HMF) in honey provide an indication of overheating under inappropriate storage conditions or aging. Conventional methods for determining HMF are cumbersome and require expensive equipment or hazardous reagents. Hence the aim of this study was to propose a new analytical tool for HMF determination in honey, using a low cost acoustic wave sensor. Volatile organic compounds (VOCs) of honey samples were extracted, using the solid phase microextraction (SPME) technique, and HMF was quantified, using a piezoelectric quartz crystal with gold electrodes coated with a layer of decamolybdodivanado phosphoric acid, sensitive to HMF. The reliability of the proposed method was confirmed after comparing the results of HMF quantification with those obtained by the conventional spectrophotometric White method, and no statistical differences were found (α=0.05).

Piezoelectric resonance sensor for the determination of ammonium in aqueous environment

In this study, a novel ammonium biosensor based on quartz crystal microbalance QCM system for determination of ammonium ion, a reaction product of urea by urease was described. Piezoelectric quartz crystals were coated with poly lactic-co-glycolic acid PLGA; 85:15 nanofiber containing fullerene C60. Then, urease EC 3.5.1.5 was immobilized on nanofibrous electrospun PLGA membrane. The nanofibers were characterized using scanning electron microscopy. Changes in the resonance frequency of the PLGA/C60–coated quartz crystal were evaluated as an indicator of changes in urea concentration. The oscillating frequency decreased accordingly to the deposition of ammonium on the quartz crystal surface. Our results indicate that the PLGA/C60 nanofiber coated piezoelectric sensor exhibited ability to determine the ammonium ion in the solution

Biomimetic piezoelectric quartz crystal sensor with chloramphenicol-imprinted polymer sensing layer

The measurement of banned antibiotic like chloramphenicol is significant for customer protection and safety. The presence of residual antibiotics in foods and food products of animal origin could pose as health hazards and affect food quality for global acceptance. In this study, the potential of a chloramphenicol sensor based on molecularly imprinted polymer (MIP) coupled with a piezoelectric quartz crystal was explored. The MIP was prepared by precipitation polymerization at 60°C. Methacrylic acid was used as monomer, trimethylolpropane trimethacrylate (TRIM) as crosslinker, and chloramphenicol as the template. Template removal on the resulting polymer was done by extraction using methanol–acetic acid. Characterization of the MIP and NIP were conducted by spectroscopic and microscopic methods. These further supported the imprinting and rebinding process of chloramphenicol to the polymer matrix. The chloramphenicol sensor was devised by spin-coating onto one side of the 10MHz AT-cut quartz crystal the MIP suspension in polyvinylchloride–tetrahydrofuran (6:2:1w/w/v) solution. Optimization of sensor response was performed by varying the type of cross-linker, amount of MIP sensing layer, curing time, and pH. The sensor exhibited good sensitivity of about 73Hz/log (conc., µgmL−1) and good repeatability (rsd<10%). A linear relationship (r2=0.9901) between frequency shift and chloramphenicol concentration in the range of 1×10−6 up to 1×10−1µg/mL was obtained. The sensor response was highly selective to chloramphenicol than with other compounds of similar chemical structures. Acceptable percent recovery was obtained for real sample analysis using the sensor. The proposed sensor could be a promising low cost and highly sensitive approach for residual chloramphenicol quantification in food products.

Thickness-shear Modes and Energy Trapping in a Rectangular Piezoelectric Quartz Resonator with Partial Electrodes

We analyze thickness-shear vibrations of a rectangular plate of quartz piezoelectric crystal for acoustic wave resonator application. The plate is partially electroded in the central region. The scalar differential equation derived by Tiersten and Smythe is employed. Exact solution for the free vibration resonant frequencies and modes are obtained. Trapped modes with vibrations mainly under the electrodes are found. The results are useful to the understanding and design optimization of crystal resonators.

Novel S-MSPQC cell sensor for real time monitoring the injury of endothelial cell by LPS and assessing the drug effect on this injury

A novel square Au microelectrode multi-channel series piezoelectric quartz crystal (S-MSPQC) cell sensor was constructed by square Au microelectrode in series connected with quartz crystal sensor in MSPQC. The experimental results showed square shape Au microelectrode was more sensitive than normally used interdigital microelectrode. New constructed S-MSPQC was successfully used for real time monitoring the injury of human umbilical vein endothelial cells which induced by lipopolysaccharide (LPS) and assessing the drug effects of two anti-oxidative vitamins, VC and VE and their combination against this injury. The detection results showed that the low concentration of LPS may promote the proliferation of the HUVEC cells at first 12h, then it caused the cell apoptosis. The pretreatment of VC or VE on the cells for 12h before adding the LPS could partially reduced the injury of LPS on HUVEC cells. The sensor detection results were all consisted with the results detected by MTT assay and microscopy observation. The synergistic effect of the combination of VC-VE on LPS-induced cell injury was also observed by sensor. Compared with the traditional biological methods, the proposed method is sensitive, label-free, non-invasive, cheap, simple, and automatic. It provides a new automatic tool for cell monitor in the field of cell biology, cytobiology, and drug effects research.

Electropolymerized molecularly imprinted polypyrrole film for sensing of clofibric acid.

Piezoelectric quartz crystals and analogous gold substrates were electrochemically coated with molecularly imprinted polypyrrole films for pulsed amperometric detection (PAD) of clofibric acid, a metabolite of clofibrate. Cyclic voltammetry data obtained during polymerization and deposited weight estimations revealed a decrease of the polymerization rate with increasing clofibric acid concentration. XPS measurements indicated that clofibric acid could be removed after imprinting with an aqueous ethanol solution, which was further optimized by using PAD. Zeta potential and contact angle measurements revealed differences between molecularly imprinted (MIP) and non-imprinted polymer (NIP) layers. Binding experiments with clofibric acid and other substances showed a pronounced selectivity of the MIP for clofibric acid vs. carbamazepine, but the response of MIP and NIP to 2,4-dichlorophenoxyacetic acid was higher than that for clofibric acid. A smooth surface, revealed by AFM measurements, with roughness of 6–8 nm for imprinted and non-imprinted layers, might be a reason for an excessively low density of specific binding sites for clofibric acid. Furthermore, the decreased polymerization rate in the presence of clofibric acid might not result in well-defined polymer structures, which could be the reason for the lower sensitivity.

A new aptamer/graphene interdigitated gold electrode piezoelectric sensor for rapid and specific detection of Staphylococcus aureus

A novel aptamer/graphene interdigitated gold electrode piezoelectric sensor was developed for the rapid and specific detection of Staphylococcus aureus (S. aureus) by employing S. aureus aptamer as a biological recognition element. 4-Mercaptobenzene-diazonium tetrafluoroborate (MBDT) salt was used as a molecular cross-linking agent to chemically bind graphene to interdigital gold electrodes (IDE) that are connected to a series electrode piezoelectric quartz crystal (SPQC). S. aureus aptamers were assembly immobilized onto graphene via the π–π stacking of DNA bases. Due to the specific binding between S. aureus and aptamer, when S. aureus is present, the DNA bases interacted with the aptamer, thereby dropping the aptamer from the surface of the graphene. The electric parameters of the electrode surface was changed and resulted in the change of oscillator frequency of the SPQC. This detection was completed within 60min. The constructed sensor demonstrated a linear relationship between resonance frequency shifts with bacterial concentrations ranging from 4.1×101−4.1×105cfu/mL with a detection limit of 41cfu/mL. The developed strategy can detect S. aureus rapidly and specifically for clinical diagnosis and food testing.

Using acoustic wave sensors to follow milk coagulation and to separate the cheeses according to the milk origin

Optimum coagulation temperature and cutting time are usually empirically defined. The use of inexpensive acoustic wave sensors to monitor milk coagulation allows monitoring the process in real time, since its early stages. Besides, data are collected with minimum disturbance, which is an advantage over other methodologies, namely rheology.Coagulation of milk was followed by measuring both the frequency and equivalent circuit resistance of a piezoelectric quartz crystal. Three types of milk, ewe, goat and cow, were coagulated using different rennets at three different temperatures. Maximum observed coagulation rate, either with plant or animal rennet, increased with temperature both for ewe and goat milk. Maximum coagulation rate was higher with plant rennet than with animal rennet at 25°C and 32°C, while the opposite was found at 50°C. The time needed to attain maximum coagulation rate was always smaller with ewe's milk than with goat's milk, and maximum coagulation rate was higher with the former. Cow's milk was much more difficult to coagulate and needed twice the rennet quantity used for ewe and goat milk.Cheese obtained with the mentioned types of milk and different rennets shows different flavours, usually perceived by experts and connoisseurs, and that an electronic nose built in our laboratory was also able to distinguish. One sensor was enough to separate cheeses made from cow, ewe and goat milk. Besides, the addition of a second sensor allowed to separate the cheeses by rennet among the ones produced with the same milk.

Multichannel series piezoelectric quartz crystal cell sensor for real time and quantitative monitoring of the living cell and assessment of cytotoxicity.

A new multichannel series piezoelectric quartz crystal (MSPQC) cell sensor for real time monitoring of living cells in vitro was reported in this paper. The constructed sensor was used successfully to monitor adhesion, spreading, proliferation, and apoptosis of MG63 osteosarcoma cells and investigate the effects of different concentrations of cobalt chloride on MG63 cells. Quantitative real time and dynamic cell analyses data were conducted using the MSPQC cell sensor. Compared with methods such as fluorescence staining and morphology observation by microscopy, the MSPQC cell sensor is noninvasive, label free, simple, cheap, and capable of online monitoring. It can automatically record the growth status of cells and quantitatively evaluate cell proliferation and the apoptotic response to drugs. It will be a valuable detection and analysis tool for the acquisition of cellular level information and is anticipated to have application in the field of cell biology research or cytotoxicity testing in the future.

Remote assessment of cultural heritage environments with wireless sensor array networks.

The logistics and cost of environmental monitoring can represent challenges for heritage managers, partly because of the sheer number of environmental parameters to consider. There is a need for a system, capable of monitoring the holistic impact of the environment on cultural materials while remaining relatively easy to use and providing remote access. This paper describes a dosimetric system based on piezoelectric quartz crystal technology. The prototype sensing module consists of an array of piezoelectric quartz crystals (PQC) coated with different metals (Fe, Cu, Ni and Sn) and includes a temperature and relative humidity sensor. The communication module involves an 802.15.4 low-power radio and a GPRS gateway which allows real time visualisation of the measurements online. An energy management protocol ensures that the system consumes very low power between measurements. The paper also describes the results and experiences from two heritage field deployments, at Apsley House in London, UK, and at the Royal Palaces of Abomey in Benin. Evaluation of PQC measurements, temperature, relative humidity and the rate of successful transmission over the communication systems are also reported.