Resonant Frequency Of Quartz Crystal Microbalance Research Articles

Study on pivot-point vibration of molecular bond-rupture events by quartz crystal microbalance for biomedical diagnostics

Bond-rupture scanning for biomedical diagnostics is examined using quartz crystal microbalance (QCM) experiments and microparticle mechanics modeling calculations. Specific and nonspecific interactions between a microparticle and its binding QCM surface can be distinguished by gradually increasing the amplitude of driving voltage applied to QCM and monitoring its frequency changes. This research proposes a mechanical model of interactions between biological molecules and a QCM substrate surface. The mechanical force required to break a biotin–streptavidin bond was calculated through a one-pivot-point bottom-up vibration model. The bond-rupture force increases with an increase of the microparticle radius, the QCM resonant frequency, and the amplitude of driving voltage applied to the QCM. The significance of the research on biological molecular bond rupture is extremely important in characterizing microbial (such as cells and virus) specificity, due to the force magnitude needed to break bonds using a transducer.

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.

Quartz Crystal Microbalance Sensor Using Ionophore for Ammonium Ion Detection

Ionophore-based quartz crystal microbalance (QCM) ammonium ion sensors with a detection limit for ammonium ion concentrations as low as 2.2 microM were fabricated. Ionophores are molecules, which selectively bind a particular ion. In this study, one of the known ionophores for ammonium, nonactin, was used to detect ammonium ions for environmental in-situ monitoring of aquarium water for the first time. To fabricate the sensing films, poly(vinyl chloride) was used as the matrix for the immobilization of nonactin. Furthermore, the anionic additive, tetrakis (4-chlorophenyl) borate potassium salt and the plasticizer dioctyl sebacate were used to enhance the sensor properties. The sensor allowed detecting ammonium ions not only in static solution, but also in flowing water. The sensor showed a nearly linear response with the increase of the ammonium ion concentration. The QCM resonance frequency increased with the increase of ammonium ion concentration, suggesting a decreasing weight of the sensing film. The detailed response mechanism could not be verified yet. However, from the results obtained when using a different plasticizer, nitrophenyl octyl ether, it is considered that this effect is caused by the release of water molecules. Consequently, the newly fabricated sensor detects ammonium ions by discharge of water. It shows high selectivity over potassium and sodium ions. We conclude that the newly fabricated sensor can be applied for detecting ammonium ions in aquarium water, since it allows measuring low ammonium ion concentrations. This sensor will be usable for water quality monitoring and controlling.

Applying the Quartz Crystal Microbalance Technique to Detect the Epithelial Cell Tight Junction Integrality of Caco-2 Cells

This paper describes a method that utilizes the quartz crystal microbalance (QCM) technique to measure the tight junction of the Caco-2 cell. The Caco-2 cells are placed on the QCM surface for cell growth and tight junction measurements. We found that the QCM resonance frequency changes less when a better tight cell junction is formed. The quantity of QCM frequency change is less than 100 Hz as the tight junction cell integrality is completed up to 15 days. The QCM and traditional detection system transepithelial electrical resistance were similar as the cell growth affects the two systems over time.

A Novel QCM-based Biosensor for Detection of Microorganisms Producing Hydrogen Sulfide

A novel piezoelectric quartz crystal microbalance (QCM) device with gas permeable membrane is proposed for the detection of microorganisms producing hydrogen sulfide (H2S). The detection theory is based on the adsorption of hydrogen sulfide onto the silver electrode of the piezoelectric crystal sensor, which causes a dramatic decrease in the resonant frequency of QCM. A 100 Hz frequency shift is chosen as the criteria value to judge the presence of microorganisms producing H2S. Factors affecting detection were investigated. Desiccant is of great practical importance in sensor response. This new biosensor can be a potential candidate for detecting bacteria which produce hydrogen sulfide.

Detection of NH3 by quartz crystal microbalance coated with TiO2

A quartz resonator with a thin TiO2 film is investigated in view of possible applications as a sensor for detecting the presence of ammonia in the ambient. A study of the sorption properties of thin TiO2 films to NH3 vapors is also presented. The films are deposited using electron beam evaporation. In order to determine the sorption ability of TiO2 to NH3, a quartz crystal microbalance (QCM) with a thin TiO2 film is used, the latter serving as a receptor for the NH3 gas. The AT-cut 16-MHz quartz resonator allows conversion of the additional mass load that occurs as a result of sorption into a frequency shift. The experiments are carried out by measuring the QCM resonant frequency shift due to the absorption of vapors from an aqueous solution of NH3 with different concentration ranging from 100 to 1000 ppm. The experimental results obtained indicate that the variation of the resonant frequency is a function of the ammonia concentration. This demonstrates that a QCM covered with a thin TiO2 layer is sensitive to ammonia vapors at room temperature and is capable of detecting NH3 concentrations in the range investigated (100-1000 ppm).

Data correction technique for using common electrochemical apparatus for the measurement of crystal impedance

Crystal impedance (CI) is a well-known technique which extends the capabilities of the quartz crystal microbalance (QCMB) technique by refining the apparent mass change reported by QCMB resonance frequency measurements into a corrected mass change and an energy loss or dissipation component. In addition to mass change, the energy loss component can provide information about additional sample properties, such as surface rigidity or roughness, as well as the viscoeleastic properties of the medium in which measurements are performed. Previous reports of CI measurements involve the use of a network analyzer, an instrument not commonly found in an electrochemical research group. Here, we describe how to utilize a more common electrochemical impedance spectroscopy (EIS) system with sufficient bandwidth for the purpose of collecting CI data. Specifically, we discuss the measurement setup required to minimize impedance mismatch and a means of mathematically correcting for the impedance of the measurement system itself. We demonstrate the utility of this system using the CI response of a Pt-coated crystal to D-fructose solutions with known density and viscosity.

A novel technique to immobilize DNA on surface of a quartz crystal microbalance by plasma treatment and graft polymerization

A quartz crystal microbalance (QCM) is well known to provide mass-sensitive devices in nanogram levels, because of the resonance frequency changes upon the adsorption on the electrode. It offers the possibility of monitoring hybridization in real time and with high selectivity. In this study, a biosensor system was developed for the detection of Vibrio parahaemolyticus via its oligonucleotide probe immobilized on the gold electrodes' surface of QCM. However, because the surface of QCM was an inorganic substance, it was difficult to immobilize the oligonucleotide probe. In this study, the plasma surface modification of QCM through deposition of hexamethyldisilazane (HMDSZ) films as an interlayer was investigated. The interlayer provided good adhesion to the substrate and had a uniform structure. The result indicates that plasma deposition was a useful technique to immobilize the oligonucleotide probe on the gold electrodes' surface via glutaraldehyde (GA) coupling. To improve immobilization, post treatments by surface grafting of acrylamide (AAm) and polyethyleneimine (PEI) treatment onto the electrodes were also performed. The result demonstrates that the shift of resonance frequency of QCM was improved via subsequent graft polymerization of AAm and PEI treatment onto the electrodes. The QCM sensor after plasma deposition and surface modification could provide detection sensitivity up to 86 ng/ml and kept at 88% detecting sensitivity after 19 days of storage at 0 °C. After washing with 0.1 M NaOH solution and 7 times of repeated use in detecting, the regeneration rate of QCM could be up to 60%.

An integrated approach for the design and synthesis of oligonucleotide probes and their interfacing to a QCM-based RNA biosensor

The quantitative determination of specific cellular messenger-RNA is extremely important both in basic and applied research, especially in diagnostic and pharmacological fields. In order to perform a direct and easy quantification of transcripts on cell extracts, the feasibility of an analytical device able to selectively detect a defined target RNA in a complex mixture while avoiding labelling, retrotranscription and amplification steps, has been explored. In particular, several aspects necessary to obtain good selectivity in target recognition, stability, reusability and sensitivity of a gene specific biosensor were considered. For the development of suitable probe-receptors, analysis of the nucleotide sequence of the target mRNA was carried out to localise the preferred binding regions. As criteria for optimisation, we selected accessibility and uniqueness. Oligonucleotide probes, designed to specifically bind these sequences, were synthesised by using particular monomers producing nuclease-resistant RNA strands with high affinity towards the target. Quartz crystal microbalance (QCM) technology was selected to realise a microgravimetric sensor able to bind the RNA under investigation through a complementary oligonucleotide probe. Covalent immobilisation of bioreceptor molecules to the transducer sensitive surface ensured a stable integration between the two. The binding ability of immobilised probes was tested evaluating their annealing behaviour with both complementary oligonucleotides and full-length target mRNA. The conditions necessary for the regeneration of biosensor were also assessed. Measurements of shift in QCM resonant frequency, performed by hybridisation experiments in liquido, demonstrate that a label-free RNA-biosensor with high specificity, reusability and the ability to give quantitative information, can be realised.

All-digital interface ASIC for a QCM-based electronic nose

An all-digital interface, application specific integrated circuit (ASIC) has been developed for the control and data sampling of a quartz crystal microbalance (QCM)-based electronic nose. The ASIC is capable of measuring QCM resonant frequency between 0 and 11MHz with a resolution of 1Hz and ±1Hz precision. The ASIC has been used to obtain measurements from polymer coated QCM sensors, in conjunction with polymer/carbon-black coated micro-resistance (μR) sensors, in the detection of primary alcohols. A full system-on-a-chip (SoC) electronic nose, currently under test, which supports arrays of eight QCM and eight μR sensors along with on-chip processing capability, is also described.

Cell spreading on quartz crystal microbalance elicits positive frequency shifts indicative of viscosity changes.

Cell attachment and spreading on solid surfaces was investigated with a home-made quartz crystal microbalance (QCM), which measures the frequency, the transient decay time constant and the maximal oscillation amplitude. Initial interactions of the adsorbing cells with the QCM mainly induced a decrease of the frequency, coincident with mass adsorption. After about 80 min, the frequency increased continuously and after several hours exceeded the initial frequency measured before cell adsorption. Phase contrast and fluorescence microscopy indicated that the cells were firmly attached to the quartz surface during the frequency increase. The measurements of the maximal oscillation amplitude and the transient decay time constant revealed changes of viscoelastic properties at the QCM surface. An important fraction of these changes was likely due to alterations of cytosolic viscosity, as suggested by treatments of the attached cells with agents affecting the actin and microtubule cytoskeleton. Our results show that viscosity variations of cells can affect the resonance frequency of QCM in the absence of apparent cell desorption. The simultaneous measurements of the maximal oscillation amplitude, the transient decay time constant and the resonance frequency allow an analysis of cell adsorption to solid substratum in real time and complement cell biological methods.

Determination of coupled solvent mass in quartz crystal microbalance measurements using deuterated solvents

A simple method is described for determining of the contribution of hydrodynamically coupled solvent to the adsorbed film mass determined in a quartz crystal microbalance (QCM) when operated in liquid. The method requires no additional apparatus and utilizes the change in QCM resonant frequency response between measurements made in nondeuterated and deuterated solvents. The mass of coupled water in a polymer film has been determined and is found to agree with that determined by XPS analysis of the dried polymer film.

‘Missing mass’ effect in biosensor's QCM applications

Nowadays, liquid applications of quartz crystal microbalance (QCM) opened a way for in situ studies of proteins, vesicles and cells adsorbed from the solution onto the QCM surface. The sensitivity of QCM to the viscoelasticity of the adsorbed biomaterial can be a reason of the experimentally observed deviation from a linear dependence of QCM resonant frequency on mass deposition (the so-called Sauerbrey relation) and can limit its application for biosensoring. Presented here rigorous theoretical analysis explains the deviation from ideal mass response of soft overlayers in the contact with liquid. The fundamental result of the theory is the analog of Sauerbrey relation for layered viscous/viscoelastic medium which can be exploited for the correct physical interpretation of QCM experimental data in biofluids, in particular for measurements of the ‘true’ surface mass of adsorbed biomolecular films. We predict a new physical effect ‘missing mass’ of the sample in liquid phase measurements and compare the results given by our theory with QCM measurements on supported membranes.

Measuring nanomechanical properties of a dynamic contact using an indenter probe and quartz crystal microbalance

A study of the contact mechanics of a probe tip interacting with a quartz crystal microbalance (QCM) has been performed, involving simultaneous measurements of normal load, displacement, and contact stiffness with changes in QCM resonant frequency. For metal–metal and glass–metal contacts in air, the QCM frequency shifts were observed to be positive, and directly proportional to the contact area as inferred from the contact stiffness. Interfacial characteristics of the probe–tip contact (elasticity, contact size, and an estimate of the number of contacting asperities) were deduced by extending a prior model of single asperity contact to the case of multiple contacts. The extended model clarifies a number of seemingly disparate experimental results that have been reported in the literature.

On the measurement of thin liquid overlayers with the quartz-crystal microbalance

We present a simple model that predicts the changes in resonance frequency and dissipation factor for a quartz-crystal microbalance (QCM) when it is coated with a viscous film that may or may not slip on the crystal. In this context, the validity of the Sauerbrey equation (change in resonance frequency α change in applied mass) is discussed. The Sauerbrey equation gives an accurate estimate of the film thickness, t f, only if (i) the film is thin compared to the shear-wave penetration depth, δ, into the liquid, i.e., t f ⪡ δ, and (ii) the film does not slide on the QCM electrode (s). We have shown that by measuring both the QCM resonance frequency and the dissipation factor simultaneously, the thickness range over which t f can be measured accurately can be extended to about 2δ for non-slipping films. If the film slips, which we have only observed for molecularly thin films, changes in dissipation factor can be used to calculate the coefficient of friction between the film and the substrate. We also show the usefulness of measuring the dissipation factor of the QCM when studying solid to liquid phase transitions.

The Role of Longitudinal Waves in Quartz Crystal Microbalance Applications in Liquids

The generation of shear waves in liquids by the quartz crystal microbalance (QCM) is evident from the influence of liquid properties on the QCM frequency and electrical characteristics. With the exception of a few reports, contributions from longitudonal waves that arise from nonuniform velocity profiles along the shear direction or nonideal contributions from crystal longtudinal and flexure modes have been largely ignored. The presence of these longitudinal components is demonstrated by the influence of a glass plate, fixed Gel to the QCM surface at a remote distance, on the QCM resonant frequency and electrical impedance characteristics. In agreement with a previous report, these effects can be observed even when the glass plate is positioned >1 cm away from the QCM, substantially longer than the shear wave decay length. Longitudinal standing waves are evident from the periodicity of the resonant frequency, inductance, capacitance, and resistance as the distance between the QCM and the glass plate. The wavelength of the standing waves agrees with that expected for the resonant frequency of the QCM and the fluid medium. The amplitude of the standing waves depends strongly upon the quartz crystal contour, as evident from extremely large frequency excursions observed for plano-convex crystals in witch energy trapping in the center of the resonator is greater than that for plano-plano crystals. Impedance analysis indicates that the frequency excursions are primarily a consequence of changes in the capacitance of the quartz crystals that result from a decrease in the compliance of the quartz resonator due to pressure exerted by the longitudinal waves. Standing waves resulting from reflection from the fluid-air interface are also observed, although the amplitude of the standing waves is smaller than the amplitude observed with the glass reflector plate owing to the larger reflection coefficient for the latter. However, the frequency excursions that result from small changes in the height of the fluid-air interface are substantial relative to frequency changes measured in typical QCM experiments. These results demonstrate that it is important to design QCM experiments to avoid contributions from longitudinal waves

Real-time measurement of anchorage-dependent cell adhesion using a quartz crystal microbalance.

An in situ technique based on the mass-sensitive piezoelectric quartz crystal microbalance (QCM) was applied to continuously monitor the attachment and detachment of anchorage-dependent mammalian cells on a metal surface. Specifically, we have demonstrated that the attachment of Vero cells to metal surfaces on the piezoelectrically active area of the QCM results in decreases in the QCM resonant frequency that can be monitored conveniently in real time. Lysis and detachment of Vero cells caused by vesicular stomatitis virus (VSV) infection can also be monitored readily. Our results demonstrate that the QCM is a viable technique for monitoring anchorage-dependent cell attachment and detachment on surfaces (caused by stimulatory, inhibitory, or cytopathic effects).