Survey on mass determination with oscillating systems: Part III. Acoustic wave mass sensors for chemical and biological sensing

We will review the application of acoustic wave mass sensors in chemical and biological sensing with focus on quartz crystal microbalance and surface acoustic wave devices. In chemical sensing, it is unlikely that a single sensor will display a selective and reversible response to a given analyte in a mixture. Alternative strategies such as use of sensor arrays and sampling devices will be discussed to improve performance. We will also discuss applications of quartz crystal microbalance as biosensor in the liquid phase.This revised version was published online in November 2005 with corrections to the Cover Date.     

压电晶体传感器的研究进展

本文简要介绍了压电晶体传感器的基本原理,以及基于质量、粘度、电导率变化的溶液分析法。重点介绍了电化学石英晶体微天平（EQCM）、压电生物传感器;对具有很大发展潜力和重要应用价值的串联式压电传感器（SPQC）、串联式表面声波电导传感器（SAW）、液隔电极式压电传感器（ESPS）等也作了简要说明。     

Acoustic Wave Mass Sensors

The application of acoustic wave microsensors for mass sensing will be reviewed with focus on the quartz crystal microbalance (QCM) and surface acoustic wave (SAW) devices. The use of QCM and SAW devices in chemical sensing as well as in the determination of solid and liquid properties will be described. In chemical sensing, it is unlikely that a single sensor with a single coating will display a selective and reversible response to a given analyte in a mixture. Alternative strategies such as the use of sensor arrays and the use of sampling devices can be used to improve performance. QCM sensors (QCMs) will oscillate under liquids; their use in under-liquid sensing will be discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Plasma Polymers Applied to Chemical Sensing

The paper describes attempts to apply plasma polymers to the development of chemical sensors. The plasma polymers were used as membranes to coat conventional conducting polymer sensors, as stand-alone chemiresistive sensors and as absorbent coatings on quartz crystal microbalances. The plasma polymers were derived from combinations of pyrrole and three silicon containing monomers. In the chemiresistive sensors, conductivity was induced in the polymer matrix by doping with iodine. The paper describes the experimental polymerization conditions, the physical characteristics of the polymers, and the application of the different polymers to sensing common volatile analytes.     

A new study of the degradation of hyaluronic acid by hyaluronidase using quartz crystal impedance technique

A new quartz crystal impedance sensing technique for the assay of hyaluronidase (HAse) activity is presented. It is based on the changes in viscosity and density during the enzymatic hydrolysis of hyaluronic acid (HA) by HAse. The variations of equivalent circuit parameters of piezoelectric quartz crystal (PQC) during the enzymatic degradation are discussed. The motional resistance shift curves indicate that the viscosity of the test solutions decreases during the hydrolysis process. The initial hydrolysis rates of HA are obtained from changes in viscosity and density as a function of incubation time. Kinetic parameters (the Michaelis constant K(m) and the maximum hydrolysis rate V(max)) of the degradation reaction are estimated by using a linear Lineweaver-Burk plot in this work. The K(m) was 0.44+/-0.03 mg.ml(-1) and the V(max) was -(5.29+/-0.36)x10(-3) kg.m(-2).s(-1/2).min(-1).     

Evaluation of the performance of sensors based on optical imaging of a chemically sensitive layer

Interest in the use of the optical properties of chemical indicators is growing steadily. Among the optical methods that can be used to capture changes in sensing layers, those producing images of large-area devices are particularly interesting for chemical sensor array development. Until now, few studies addressed the characterization of image sensors from the point of view of their chemical sensor application. In this paper, a method to evaluate such performance is proposed. It is based on the simultaneous measurement of absorption events in a metalloporphyrin layer with an image sensor and a quartz microbalance (QMB). Exploiting the well-known behaviour of QMB, comparison of signals enables estimation of the minimum amount of absorbed molecules that the image sensor can detect. Results indicate that at the single pixel level a standard image sensor (for example a webcam) can easily detect femtomoles of absorbed molecules. It should therefore be possible to design sensor arrays in which the pixels of images of large-area sensing layers are regarded as individual chemical sensors providing a ready and simple method for large sensor array development.     

Ionic liquids as selective depositions on quartz crystal microbalances for artificial olfactory systems—a feasibility study

A room-temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium hexafluorophosphate, was investigated as a selective deposition for quartz crystal microbalances. RTILs constitute versatile matrices of tuneable physicochemical properties providing a high solute mobility compared to polymer matrices, and hence in principle short response and desorption times. This paper explores the feasibility of using RTIL-based quartz crystal microbalances as vapour sensors with particular focus on the physicochemical interactions between the RTIL and a model solute, ethyl acetate. Preliminary experiments were conducted and proved an excellent baseline recovery of the sensor. The transient sensor response was modelled using a basic mass transport equation which proved the simplicity of the system when compared to polymer coatings. The diffusion coefficient of ethyl acetate was calculated to be 10.8·10^− 11 m²·s^− 1, which was one order of magnitude higher than in a common polymeric deposition material, polydimethylsiloxane. However, it is pointed out that care must be taken when interpreting the sensor signal upon dissolution of a complex vapour; absorption of solutes into the RTIL can give rise to viscosity changes which affect the sensor signal and hence overlap with the response to the solute mass absorbed. Nevertheless, for simple sample vapours we believe that quartz resonators can also be a complementary and cheap method for investigating basic mass transport phenomena.     

Gas-sensing System Using an Array of Coated Quartz Crystal Microbalances with a Fuzzy Inference System

Quartz crystal microbalances have high mass sensitivities. Their application in gas sensing has been limited because they are required to have both high selectivity and reversibility. Yet by the inherent nature of their operation these properties are mutually exclusive. One approach to this problem is to use an array of quartz crystal microbalances. We have used an array of six coated quartz crystal microbalances for the classification of methanol, propan-1-ol, butan-1-ol, hexane, heptane and toluene. A novel classification scheme using fuzzy membership functions was found to be highly efficient. This revised version was published online in July 2006 with corrections to the Cover Date.     

Oscillating Frequency Response of a Langasite Crystal Microbalance in Liquid Phase

The frequency responses of a langasite crystal microbalance （LCM） in liquid phase were investigated. It was shown that the LCM possessed much stronger oscillating ability in liquid phase than that of the commonly used quartz crystal microbalance （QCM）. The frequency shifts of the LCM to the changes in mass loading, as well as viscosity and density of the liquid were measured. The LCM was applied to monitor the adsorption process of an ionic liquid film to ethanol vapor.     

Principles of quartz crystal microbalance/heat conduction calorimetry: Measurement of the sorption enthalpy of hydrogen in palladium

A sensitive new measurement technology is described which combines calorimetry, gravimetry, and rheology applied to chemical reactions in thin films: quartz crystal microbalance/heat conduction calorimetry (QCM/HCC). The quartz crystal microbalance/heat conduction calorimeters constructed so far simultaneously measure heat generation, mass uptake or release, and viscoelastic property changes in the same, sub-milligram solid film sample when gases interact with the film in an isothermal surrounding. It is possible to measure the energetics of formation of a single layer of adsorbed molecules on a gold surface with this technique. The principles of operation of both the mass and the heat flow sensor are described, and one implementation of the combined sensor and apparatus and its electronics is presented. Methods for calibration and the preparation of thin sample films are summarized. As an illustrative example, the determination of the sorption enthalpy of hydrogen in a 25 °C palladium film of 140 nm thickness is discussed in detail. Other examples of the operation of the QCM/HCC are tabulated.     

Detecting aniline in air in systems based on piezoelectric quartz crystal resonators modified with poly(ethylene glycol succinate) under static and dynamic conditions

The optimal conditions have been found for aniline sorption on a film of poly(ethylene glycol succinate) by the piezoelectric quartz crystal microbalance method using bulk acoustic wave sensors based on AT-cut quartz crystals under static and dynamic conditions. The dependence of the analytical signal of the quartz crystal resonator on the modifier film mass, the volumetric flow rate of the carrier gas (air), and the sorption temperature has been investigated.     

Humidity sensing characteristics of Sn doped Zinc oxide based quartz crystal microbalance sensors

The electrical, optical and humidity sensor properties of nanostructured ZnO samples were investigated. The structural properties of Sn doped ZnO samples were characterized by X-ray diffraction and atomic force microscopy. It was found that the all samples have a hexagonal crystal structure. The electrical conductivity of the samples indicates that undoped and Sn doped ZnO samples exhibit the semiconducting behavior. The optical absorption method was used to determine the optical band gaps of the samples. The optical band gap and activation energy values of the ZnO samples were changed with Sn doping. The ZnO based on quartz crystal microbalance humidity sensors were prepared and sensing properties of the sensors were changed with Sn doping. The response time required to reach 70 % is about 13–16 s, while the recovery time from 70 to 30 % RH is about 13–15 s. The fast response of the sensors is due to easy diffusion of water molecules between ZnO nanopowders. The prepared sensors have a high reproducibility and sensitivity for humidity sensing applications.     

Nanoengineered glycan sensors enabling native glycoprofiling for medicinal applications: towards profiling glycoproteins without labeling or liberation steps

Nanoengineered glycan sensors may help realize the long-held goal of accurate and rapid glycoprotein profiling without labeling or glycan liberation steps. Current methods of profiling oligosaccharides displayed on protein surfaces, such as liquid chromatography, mass spectrometry, capillary electrophoresis, and microarray methods, are limited by sample pretreatment and quantitative accuracy. Microarrayed platforms can be improved with methods that better estimate kinetic parameters rather than simply reporting relative binding information. These quantitative glycan sensors are enabled by an emerging class of nanoengineered materials that differ in their mode of signal transduction from traditional methods. Platforms that respond to mass changes include a quartz crystal microbalance and cantilever sensors. Electronic response can be detected from electrochemical, field effect transistor, and pore impedance sensors. Optical methods include fluorescent frontal affinity chromatography, surface plasmon resonance methods, and fluorescent carbon nanotubes. After a very brief primer on glycobiology and its connection to medicine, these emerging systems are critically reviewed for their potential use as core sensors in future glycoprofiling tools.     

Tailoring the structure of metal oxide nanostructures towards enhanced sensing properties for environmental applications

The present article reviews recent works in our laboratory about the sensing properties to toxic gases using nanostructured WO(3), TiO(2), FTiO(2), and CuO functionalized quartz crystal microbalance (QCM) sensors. WO(3) and TiO(2) functionalized QCM sensors have much shorter response time than those functionalized by conventional hydrogen-bond acidic branched copolymers for detection of dimethyl methylphosphonate (DMMP). FTiO(2) functionalized QCM sensors can improve the gas sensing characteristics by shortening the response time but at the price of partial irreversibility. The sensing mechanism was examined by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Varied CuO nanostructures were synthesized by simple modulation of reaction conditions. All the as-prepared CuO was applied on QCM resonators and explored for HCN sensing. Surprisingly, responses of all the sensors to HCN were found to be in an opposite direction as compared with other common volatile substances, offering excellent selectivity for HCN detection. The sensitivity was very high, and the response and recovery were very fast. Comparison of the specific surface areas of CuO nanostructures showed that CuO of higher surface area is more sensitive than that of lower surface area, indicating that the specific surface area of these CuO nanostructures plays an important role in the sensitivity of related sensors. Based on experimental results, a sensing mechanism was proposed in which a surface redox reaction occurs between CuO and Cu(2)O on the CuO nanostructures reversibly upon contact with HCN and air, respectively. The CuO functionalized QCM sensors are considered to be a promising candidate for trace HCN gas detection in practical applications.     

Temperature‐Induced Swelling and De‐swelling of Thin Poly(N‐Isopropylacrylamide) Gels in Water: Combined Acoustic and Optical Measurements

The temperature‐induced swelling and deswelling of thin layers of poly(N‐isopropylacrylamide) gels in water was measured as a function of cross‐link density and thickness. The collapse behavior was probed via an in situ combination of a quartz‐crystal microbalance (QCM) and a surface plasmon resonance (SPR) spectrometer. The shifts in the SPR coupling angle are explained in terms of decrease of the refractive index inside the film. The evanescent optical wave mostly probes the film's interior properties. The acoustic shear wave emanating from the quartz resonator, on the other hand, propagates to the outer surface of the film, unless the film is very dilute. The acoustic data are dominated by the changes in thickness, rather than in its viscosity. The combination of acoustic and optical measurements, therefore, provides complementary information on the film that can be exploited for sensing applications.     

In Situ Acquisition of Equivalent Circuit Parameters of Crystal Resonance during Copper Deposition and Dissolution in Acidic Solution by Electrochemical Quartz Crystal Impedance System

Thequartzcrystalimpedancetechniqueisapowerfulmethodtocharacterizecrystalresonancesincemultipleinformationaboutcrystalresonanceincludingtheresonantfrequencyandchangesinsomephysicaland/orchemicalpropertiesofthetestsystemcanFigure1.Equivalentelectricalc...     

Latex piezoelectric immunoassay: detection of agglutination of antibody-bearing latex using a piezoelectric quartz crystal

A method for immunoassay of CRP (C-reactive protein) was developed using a piezoelectric quartz crystal. Previous immunoassays using a piezoelectric crystal have required the formation of a thin film on the crystal, to which an antibody is affixed. The occurrence of antigen-antibody reaction increases the weight attached to the crystal surface, which causes a reduction in the oscillation frequency. In our method, the frequency reduction was observed using antibody-bearing latex without any film. One possible mechanism of the frequency change is that the crystal acts as a sensing apparatus for viscosity or density change in the solution due to aggregation of latex particles. The detection limit was almost the same as that for latex photometric immunoassay (LPIA). The present method has been designated as latex piezoelectric immunoassay (LPEIA).     

Peculiarities of microweighing of trace quantities of alkylamines on polymer and solid-state thin films

The development of various devices with sensing elements operating on the basis of quartz crystal microbalance technique for the determination of ammonia and volatile amines in air have been considered. The results on the formation of selective layers of piezoelectric sensors with the specified properties have been presented. The influence of the nature of modifier, solvent, sorbate, and method of their formation on the piezo element on the sorption properties of thin films has been considered. The mechanism of interaction in the studied systems has been discussed relying on the results of quartz crystal microbalance measurement and microstructural studies at different stages of sorption.     

A non-potentiometric sensing method for the determination of pentoxyverine with PQC sensors based on ion-pair complexes.

The construction and general performance characteristics of three piezoelectric quartz crystal sensors responsive to the pentoxyverine are described here. This kind of non-potentiometric sensing method is based on use of ion-pair complexes of the pentoxyverine cation with three counter anions, namely, tungstophosphate, tetraphenylborate and picrolonate. The complexes were embedded in a PVC matrix. Adsorption of the pentoxyverine ion on the complex caused a frequency decrease of the crystal. The frequency decrease was proportional to the amount of adsorbed analyte. The influencing factors were investigated in detail, and then optimized. The proposed sensors exhibit reasonable selectivity and a higher sensitivity than the potentiometric sensors. For a sensor modified with pentoxyverine-phosphotungstate, the calibration graph was linear over concentration of 1.0 x 10(-7) - 5.0 x 10(-5) M with a detection limit of 6 x 10(-8) M at pH 5.4.     

Simultaneous impedance measurements of two one-face sealed resonating piezoelectric quartz crystals for in situ monitoring of electrochemical processes and solution properties

Through admittance measurements of two piezoelectric quartz crystals in parallel on one impedance analyzer and then non-linear fitting according to an equivalent circuit of two parallel Butterworth-Van Dyke circuits, we have simultaneously obtained accurate and precise impedance responses of two one-face sealed crystals to changes in solution density and viscosity, temperature, conductance, and/or electrode mass. A series of sucrose aqueous solutions, ferri-/ferrocyanide redox switching, hot water cooling, a series of NaClO₄ aqueous solutions, bovine serum albumin adsorption and silver electrodeposition/stripping were selected as model systems for such purposes. Galvanostatic charging/discharging reactions at positive and negative poles in a Ni-Zn battery were synchronously monitored, with some quartz crystal microbalance (QCM) insights into the second reduction process of nickel hydroxide film. In all cases, the crystal immersion angle effect was found to be negligible. The present method as a versatile one is highly recommended for informative two-electrode monitoring of two concurrent chemical or biological events, or for check and/or compensation of effects due to solution density, viscosity, temperature and/or conductance during QCM researches.