Quartz Crystal Microbalance Electrode Research Articles

Imprinting unique motifs formed from protein–protein associations

Lysozyme and cytochrome c were imprinted in aqueous media, both as individual proteins and in combination, together with the functional monomer 3-aminophenylboronic acid (APBA) using ammonium persulphate as the initiator. The polymers were formed as films on the gold surfaces of quartz crystal microbalance (QCM) electrodes. It was shown that the lysozyme imprinted polymer was capable of selective template recognition. Micro-calorimetry measurements were used to determine the ratio of lysozyme and cytochrome c giving rise to the maximum enthalpy change when combined in the presence of the functional monomer. Using this procedure a maximum enthalpic change was found when the two proteins were present in an equimolar ratio. A polymer, formed by jointly imprinting the proteins in this ratio, exhibited minimal recognition for the individual template proteins, but was however able to recognise them in combination, suggesting that the proteins when imprinted together interact to form a ‘new’ imprintable motif. The introduction of a series of protein solutions, comprising the imprint proteins in various ratios, to the lysozyme/cytochrome c imprinted films, showed that the films exhibit maximum affinity towards the proteins when they are presented in approximately the same mole ratio (57% cytochrome c and 43% lysozyme) as was used to form the original imprint (equimolar ratio). Frequency response profiles of the QCM electrodes carrying the films, as a function of time, showed the establishment of a new stable baseline (−4.3 Hz) after the electrode was challenged with template protein (1.39 × 10 −9 mol) in less than 3 min.

Electrospun fibrous polyacrylic acid membrane-based gas sensors

Electrospun fibrous polyacrylic acid (PAA) membranes were studied as sensing material coated on quartz crystal microbalance (QCM) for ammonia detection at ppb level. The fibrous membranes with different morphology can be deposited on the electrode of QCM by electrospinning the PAA solutions with various solvent composition of H 2O and ethanol. The results of sensing experiments indicated that the sensitivity of the fibrous membranes coated QCM (FM-QCM) sensors was four times higher than that of the casting films coated QCM (CF-QCM) sensors. Meanwhile, the FM-QCM sensors exhibited high sensitivity towards low concentration of ammonia, as low as 130 ppb at the relative humidity of 40%. The pre-sorbed water in fibrous membranes was proved to be the key factor to affect the sensitivity of FM-QCM sensors for ammonia. The sensor performance has been found to depend on the morphology of the fibrous membranes, concentration of ammonia, coating load of the fibrous membranes on QCM, and relative humidity. Preliminary study of the stability investigation was also presented.

QCM–FIA with PGMA coating for dynamic interaction study of heparin and antithrombin III

In this work, we describe a method of constructing a film of linear poly(glycidyl methacrylate) (PGMA) polymer onto the surface of quartz crystal microbalance (QCM) electrode as a coating material that allows easy coupling of heparin molecules onto the electrode and facilitates the determination of the interaction between heparin and antithrombin III (AT III). The PGMA film was characterized with atomic force microscopy (AFM) and infra-red spectroscopy. The coupling of heparin was accomplished in one step solution reaction. A home-made quartz crystal microbalance-flow injection analysis (QCM-FIA) system with data analysis software developed in our laboratory was used to determine the interaction. The interactions between immobilized heparin and AT III were studied with various concentrations under various conditions. The obtained constants are kass=(1.49+/-0.12)x10(3)mol-1ls-1, kdiss=(3.94+/-0.63)x10(-2)s-1, KA=(3.82+/-0.33)x10(4)mol-1l.

Kinetics and morphology of formed gypsum

Calcium sulfate dihydrate scale was electrochemically deposited from supersaturated solutions on gold electrodes (probe) of an electrochemical quartz crystal microbalance (QCM). From measurements of the induction period for the gypsum nucleation, the interfacial tension was calculated. The dependence of the induction period on temperature allowed determining the activation energy. From the dependence of the induction period on temperature and supersaturation, it was possible to distinguish between the homogeneous and heterogeneous nucleation mechanisms. It was also observed that the induction period depends highly on the lattice cation/anion molar ratio. This dependence is more important for the lower supersaturations. The critical size r c represents the minimum size of a stable nucleus. Particles smaller than r cc dissolve or evaporate and particles larger than r cc continue to grow. It was observed that r cc decreased with increasing temperature for the heterogeneous nucleation process, but it had a constant value for the homogeneous nucleation process. From the SEM photos, it was observed that long induction times allow the growth of larger crystals while a shorter induction period permits smaller crystals and that the lattice cation/anion molar ratio did not effect the size of the crystals that were formed. Finally, this work demonstrated that the QCM is a very attractive instrument to identify precipitation mechanisms and to measure the amount of deposited crystals.

Study of deposition of gas sensing films on quartz crystal microbalance using an ultrasonic atomizer

A novel method for depositing gas sensing films on quartz crystal microbalance electrodes was developed. The method is based on the production of a fine mist of the solution with the sensing material by means of an ultrasonic atomizer. The mist is transported by a dry air flow to the quartz substrate allowing its deposition. The responses of the sensors are compared with those fabricated by spray coating method. It was found that even liquid films such as Apiezon L that were not stably deposited on polished gold electrodes by the spray method could be stably deposited using the atomizer, and an improvement of the reproducibility and sensitivity of the sensor response was achieved.

Determination of Acetonitrile in Air Using a Piezoelectric Quartz Crystal Microbalance

The affinity of acetonitrile to different adsorbents used as modifiers of quartz crystal microbalance electrodes was estimated from quantitative sorption parameters. A piezoelectric quartz crystal microbalance with electrodes modified with a squalane solution in hexane was proposed for determining acetonitrile in air at a level of 0.5 MPC. The conditions of the formation of sensitive films (modifier weight and solvent) were optimized, and the interfering effect of alkyl acetates was studied.

Regioselective imprinting of anthracenecarboxylic acids onto TiO 2 gel ultrathin films: an approach to thin film sensor

Ultrathin films of titanium oxide gel were imprinted with aromatic carboxylic acids, e.g. 4-(4-propyloxyphenylazo)-benzoic acid (C 3AzoCO 2H) and anthracenecarboxylic acids (2-AnCO 2H and 9-AnCO 2H), by repeatedly immersing a gold-coated quartz crystal microbalance (QCM) electrode or a quartz plate in a mixed solution of given carboxylic acids and titanium- n-butoxide (Ti(O- n Bu ) 4) in toluene/ethanol. Regular film growth was confirmed by frequency shifts of QCM measurement and by appearance of the absorption for aromatic moieties in UV-visible spectroscopy. The template molecules were completely removed upon treatment with 1% ammonia solution. The resulting films showed sensitive mass increases for guest binding of various carboxylic acids, and the isomeric structure of the two anthracenecarboxylic acids (2- and 9-isomers) was discriminated by the imprinted films. Together with our previous results, major molecular selectivities—functional selectivity, structural selectivity, regioselectivity, and enantioselectivity—are all achieved by imprinted TiO 2 gel films.

The application of CNT/Nafion composite material to low humidity sensing measurement

Composite humidity sensing films were made from carbon nanotube (CNT) and Nafion. The sensing films were prepared using the spin-coating method. Sensing films coated on the electrode of a Quartz Crystal Microbalance (QCM) were used for low humidity measurement. This low humidity system was set up with a divided flow generator and calibrated by an optical chilled dew-point hygrometer in the measuring range from 8.50 to 15,300 ppm v. The detection limit of this sensing system was about 15.76 ppm v. In this low humidity sensing system, the CNT/Nafion sensing material coated on the gold electrode of QCM showed excellent sensitivity, linearity (Rsqr = 0.995), short response and recovery time (less than 5 s, at testing point of 15.76 ppm v).

Fabrication of miniaturized bi-convex quartz crystal microbalance using reactive ion etching and melting photoresist

In this paper, miniaturized bi-convex quartz crystal microbalance (QCM) has been fabricated using reactive ion etching (RIE) and melting photoresist technology. Due to the convexity of the resonator surface and the small size of the excitation electrode, the energy of the oscillation is trapped at the center so that very little dissipation occurs at the edge. The fabricated bi-convex QCM has superior resonant characteristics compared with a QCM without the bi-convex formation. For example, the QCM with a high-quality value (76 000) was realized for a 1 mm-diameter electrode QCM with 1.6 μm-deep and 2 mm-diameter convex formation on both sides. A spurious mode around a fundamental vibration mode became very small or nearly negligible. This technology is useful from the viewpoint of mass production because it does not require polishing. The manufactured bi-convex QCM can be used for sensing liquid properties.

Rotating ring-disk electrochemical quartz crystal microbalance: a new tool for in situ studies of oxide film formation

A rotating ring-disk electrode has been made by sputter depositing the disk and ring materials onto a quartz crystal substrate through masks. The design provides for separate electrical leads to ring and disk on the quartz surface. The collection efficiency determined experimentally with ferricyanide was not significantly affected by the presence of the leads. The new RRD electrode design permits the development of a a rotating ring-disk electrochemical quartz crystal microbalance electrode (RRD/EQCM) device for the simultaneous measurement of the disk current, the frequency shift of the quartz crystal and the ring current. The collection efficiency for oxygen was studied with gold disk and ring electrodes and was found to be significantly lower than that for ferricyanide. Using a titanium disk in combination with a gold ring, potential sweep experiments using the RRD/EQCM were carried out on the anodization of titanium in sulfuric acid. Above a potential of 3 V a mass loss was observed at the disk and oxygen was detected at the ring.

気－水界面での生体分子認識を重さで測る－水晶発振子マイクロバランス法の応用－

We have developed a quartz-crystal microbalance (QCM), in which fundamental frequency decreases with increasing mass on the electrode in aqueous solution. When a 27 MHz QCM is employed, a mass of 0.62 ng/cm2 deposited on the electrode decreases the frequency by 1 Hz. Thus, when the host molecule is immobilized on the QCM electrode, the binding behavior of guest molecules could be observed in nanogram level in aqueous solution. In this review, we report that the biomolecular recognitions and reactions at the water-substrate interface by using the QCM technique, such as 1) protein binding to a sugar lipid monolayer at the air-water interface, and 2) oligo nucleotides biding to a nucleolipids monolayer at the air-water interface.

水晶結晶微量天秤とＬａｎｇｍｕｉｒ‐Ｂｌｏｄｇｅｔｔ法により評価した油汚れに対する洗浄力（原標題は英語）

The titled assessment was conducted using a quartz crystal microbalance (QCM) and the Langmuir-Blodgett (LB) method. The gold electrodes of QCM were coated with cellulose acetate, nylon 6 or polyethylene film by spin-coating. Spreading monolayers of long-chain fatty acid as oily contaminants on water were transferred onto spin-coated polymer film. LB films of arachidic acid were ultrasonically cleaned in aqueous solution. Detergency was determined based on the frequency change of the QCM due to cleaning. Detergency was greatest for cellulose acetate, followed by nylon 6 and polyethylene. For all films, detergency increased with the addition of ethanol, surfactant and alkali. Detergency is discussed in relation to contact angle of aqueous solution on polymer film. Liquid introduction between LB film and the polymer surface in the zone of contact appeared to be a significant factor in the removal of LB film from the polymer surface.

Quartz crystal microbalance and infrared reflection absorption spectroscopy characterization of bisphenol A absorption in the poly(acrylate) thin films.

The absorption process of bisphenol A (BPA) in a number of poly(acrylate) thin films, such as poly(2-methoxyethyl acrylate) (PMEA), poly(ethyl acrylate) (PEA), poly(n-butyl methacrylate) (PBMA), and poly(methyl methacrylate) (PMMA), has been investigated by quartz crystal microbalance (QCM) and infrared reflection absorption spectroscopy (IRRAS) measurements. Both QCM and IRRAS measurements show that the BPA molecules absorb in PMEA, PEA, and PBMA thin films but not in PMMA thin film. The differences in the BPA absorption behavior are mainly attributed to the difference in the glass transition temperature (T(g)) between these polymers. This absorption behavior also depends on the BPA concentration and polymer film thickness. Furthermore, IRRAS characterization demonstrates that the hydrogen bonding is formed between the hydroxyl group in BPA and the carbonyl group in the poly(acrylate) thin films. BPA molecule absorbed in these polymer thin films can be removed by ethanol rinse treatment. By optimizing experimental conditions for the QCM electrode modified by PMEA thin film, detection limitation of approximately 1 ppb for BPA can be realized by the in situ QCM measurement. This method is expected to be a sensitive in situ detection way for trace BPA in the environmental study.

Conventional detection method of fibrinogen and fibrin degradation products using latex piezoelectric immunoassay

We developed a conventional immunosensor for fibrinogen and fibrin degradation products (FDP) to combine a quartz crystal microbalance (QCM) with the agglutination reaction of immunized latex beads. FDP induced an immunoreaction due to anti-FDP antibody immobilized latex particles. We successfully measured FDP concentration of in human serum within 10 min by QCM method. The detection range of QCM immunosensor is covered with screening concentration of FDP in serum (<10 μg/ml of FDP). The time course of latex agglutination obtained from QCM immunosensor is synchronized to that of latex photometric immunoassay. SEM was used to observe the surface of QCM that applied FDP serum. The size of latex particles agglutinated on the QCM electrode increased concomitant with FDP concentration. Frequency shift on immunoreaction explains the increased adsorption amount of agglutinated latex on QCM.

Film thickness studies for the chemically synthesized conducting polyaniline

The chemical oxidation of aniline with ammonium persulphate (APS) in aqueous acidic medium to form polyaniline (PANI) films has been studied using the quartz crystal microbalance (QCM) technique. PANI films can also grow onto glass supports immersed in the reaction mixture during the polymerization. The optical absorption for these films was measured. Multilayer deposition of polymer films onto the gold electrode of QCM and onto the glass supports from consecutive repetitive treatments by the reaction mixture containing aniline and APS, were studied. The induction period, the yield and the growth rate of the polymer films during the multilayer deposition were discussed. A relation between the thickness of the films determined, from QCM technique and the optical absorption of the films was established. The electrical conductivity of the PANI films was also measured.

In vitro selection of N peptide-binding RNA on a quartz-crystal microbalance.

We report here an in vitro selection of a hairpin loop-RNA bound to N Peptide from bacteriophage lambda on a 27 MHz quartz-crystal microbalance (QCM) to study an interaction between an RNA structure and an RNA-binding peptide. The N Peptide was immobilized on a QCM electrode and specific RNAs binding to the peptide were selected from a GNRNA pentaloop-randomized RNA library with in situ monitoring of selection processes using a QCM. After the 5th round selection, the consensus sequences including a GCGCA loop were obtained from the pentaloop library. This RNA sequence was different from a binding site of a native N Protein (boxB RNA).

The reaction of cytochrome c with bovine and Bacillus stearothermophilus cytochrome c oxidase immobilized in electrode-supported lipid bilayer membranes

Stable lipid bilayer membranes containing cytochrome c oxidase from two sources (i.e. bovine and Bacillus stearothermophilus) have been immobilized on gold quartz crystal microbalance (QCM) electrodes. The immobilized oxidase can be characterized using direct electrochemical methods. Amperometric flow injection analysis data of reduced cytochrome c reacting at oxidase-modified electrodes indicate that the kinetics are non-hyperbolic, which agrees with previous results found in the literature. The kinetics of the cytochrome c oxidase/cytochrome c redox couple are characterized by a high and low affinity regime each having a distinct K m value. The rate of mediated electron transfer from solution-resident reduced cytochrome c to the electrode is also affected by ionic strength. Electrochemical and QCM results suggest that the fastest rates of electron transfer are observed when the ionic strength is low enough to allow facile binding between the protein and the enzyme but high enough to allow the protein to dissociate from the oxidase.

Fabrication and Characterization of Diamond Quartz Crystal Microbalance Electrode

Boron-doped diamond film on a quartz crystal electrode was prepared by a reflow technique. The mass sensitivity of this diamond-quartz crystal microbalance (QCM) sensor was determined by performing electrodeposition. This novel electrochemical QCM sensor was quite stable under several electrochemical experimental conditions. Its wide potential window and significantly low background current are just the same as the performance of a diamond electrode. We also showed that the fabricated diamond-QCM electrode worked satisfactorily as a useful tool for electrochemical microgravimetry by examining hydrogen evolution, oxygen evolution, and oxidation of the diamond surface in acidic solutions. It was found that evolved inserted into the bulk of as-grown diamond with a storage volume of 0.06 mol/dm3 in 0.5 M HCl solution, after sweeping the potential from 0 to −3 V at a scan rate of 10 mV/s, in contrast to O-terminated diamond-QCM, which inhibited hydrogen intercalation. © 2002 The Electrochemical Society. All rights reserved.

MOLECULAR RECOGNITION OF NUCLEOBASES ATTACHED TO SELF-ASSEMBLED MONOLAYERS DETECTED BY CHEMICAL FORCE MICROSCOPY AND QUARTZ CRYSTAL MICROBALANCE

In order to develop a new DNA sequencing method by using chemical force microscopy (CFM), we have investigated the interaction of the hydrogen bonding between surfaces of nucleobase self-assembled monolayers (SAMs) and AFM-tips modified with the nucleobases. The two different adhesion forces, the jump-in force and pull-off force, between the AFM-tip modified with cytosine-SAM and the surfaces of four kinds of nucleobase SAMs were measured in water (20°C) by CFM. The adsorption of poly (C) onto a nucleobase-SAM on a gold electrode of quartz crystal microbalance (QCM) was measured as resonance frequency changes. The relative relation among four bases showed similar tendency in the adhesion force measured by the cytosine AFM-tip and in the adsorption amount of poly (C) on the QCM electrode as well as in the theoretically calculated interaction energies between two nucleobases.

A piezoelectric gene-sensor using actinomycin D-functionalized nano-microspheres as amplifying probes

A gene-sensing system has been developed using actinomycin D-functionalized magnetic nano-microspheres, which can interact with double-stranded DNAs (dsDNAs) anchored on the gold film electrode of an electrochemical quartz crystal microbalance (EQCM). Actinomycin D acts as a guide that leads heavy microspheres onto the dsDNAs at the EQCM film. A magnetic separation shelf could separate unreacted microspheres conveniently. The modification and DNA hybridization at EQCM electrodes were examined by microgravimetric and electrochemical methods. In this way, an outstanding change in frequency decrease has been monitored owing to the mass increase on the EQCM electrodes. The limit for the determination of target DNA could be improved from 6.2×10 −8 to 2.0×10 −12 mol l −1 by the amplifying technique.