Quartz Crystal Microbalance Electrode Research Articles

Electrochemical Analysis of Cell Plasma Membrane Cholesterol at the Airway Surface of Mouse Trachea

Electrochemical detection of plasma membrane cholesterol at the surface of excised mouse trachea tissue is reported. Cholesterol oxidase is covalently linked to an 11-mercaptoundecanoic acid submonolayer on the platinum electrode surface. The cholesterol oxidase-modified electrodes show steady-state responses for cholesterol in solution at physiological temperatures. Experiments for direct contact between the cholesterol oxidase-modified electrode and the surface of excised trachea tissue at 37 degrees C indicate steady-state responses that are largely independent of the position of contact on the tissue surface. Tissue samples are mounted on a quartz crystal microbalance electrode to gauge contact force between the electrode and the tissue surface, and the steady-state electrode response for tissue cholesterol is shown to be largely independent of the contact force. Trachea tissue excised from a mouse model of cystic fibrosis, which is known to exhibit evaluated cholesterol in airway cells, shows an electrode response that is approximately 40% larger than the response observed at wild-type mouse trachea tissue.

In situ growth of nanogold on quartz crystal microbalance and its application in the interaction between heparin and antithrombin III

A novel biosensor for detecting antithrombin III (AT III) was constructed based on in situ growth of nanogold on the gold electrode of quartz crystal microbalance (QCM). The growth process of nanogold was monitored by QCM in real time. Heparin was used as the affinity ligand and immobilized onto the nanogold modified gold electrode. A flow injection analysis–quartz crystal microbalance (FIA-QCM) system was used to investigate the relationship between nanogold growth and the AT III response. Along with the nanogold particle growth within initial 5 min, the amount of heparin immobilized onto the nanogold modified electrode increased quickly. Correspondingly, the frequency response to AT III binding increased rapidly at the same time. After that, both the immobilized amount of heparin and the sensor response to AT III decreased gradually. Compared with the directly immobilized large nanogold particles, the in situ grown particles with the same size occupy more sensor surface, resulting in higher frequency shifts to AT III in the interaction study between heparin and AT III. The obtained constants of AT III binding to immobilized heparin are k ass = ( 1.65 ± 0.12 ) × 10 3 L / mol s , k diss = ( 2.63 ± 0.18 ) × 10 −2 1 / s and K A = ( 6.27 ± 0.42 ) × 10 4 L / mol .

Monitoring the drown-out crystallization of sodium chloride on a DNA-modified surface

The drown-out crystallization of sodium chloride is conducted on a DNA-modified quartz crystal microbalance (QCM). To investigate the crystallization behavior of NaCl on a DNA template, a thiol-modified DNA oligomer is self-assembled on a gold electrode of QCM. The resonant frequency shift and resonant resistance of the DNA-modified QCM are measured with the continuous injection of ethanol in the NaCl saturated solution, and compared with those of a bare QCM without any modification. F– R diagram is interpreted to analyze a detailed mechanism of the QCM response change for the crystallization. An atomic force microscope (AFM) technique is also used to confirm the procedure of the NaCl crystallization on the DNA template. From these results, it is found that the QCM sensor system could be applied to monitor the NaCl crystallization in the aqueous solution, and to detect a super-saturation point or degree.

Surface Adsorption and Replacement of Acid-Oxidized Single-Walled Carbon Nanotubes and Poly(vinyl pyrrolidone) Chains

Quartz crystal microbalance (QCM) was used to investigate the adsorption of acid-oxidized single-walled carbon nanotubes (Ox-SWNTs) and poly(vinyl pyrrolidone), PVP. It was found for the first time that Ox-SWNTs adsorbed onto the QCM electrode can be effectively replaced by PVP chains in an aqueous solution. This replacement process was also investigated by atomic force miscroscopic (AFM) imaging, which shows good agreement with the QCM measurements. This study provides powerful tools for fundamental investigation of polymer-nanotube interactions and for controlled design/fabrication of functional polymer-nanotube surfaces for potential applications.

Immersion‐Angle Dependence of the Resonant‐Frequency Shift of a Quartz Crystal Microbalance in Three Types of Newtonian Liquids

The present work reports the new characteristics of the immersion‐angle dependence of the resonant‐frequency shift (ΔF) of the one‐face sealed quartz crystal microbalance (QCM) in three types of Newtonian liquids, i.e., sucrose, glucose, and glycerol solutions. Below some 1.80×10−2 g cm−2 · s−1/2, the ΔF values are dependent on the immersion angles in all solutions. However, we have found that the transition phenomenon of ΔF occurs between 1.78×10−2 and 4.80×10−2 g · cm−2 · s−1/2 in the sucrose solution, between 1.75×10−2 and 4.34×10−2 g · cm−2 · s−1/2 in the glucose solution and between 1.83×10−2 and 3.03×10−2 g · cm−2 · s−1/2 in the glycerol solution, respectively. Moreover, above the concentrations of the end points of the transition phenomenon, the ΔF values of the sucrose solution are equal to those of 90° at all immersion angles. On the other hand, those of the glucose and the glycerol solutions are the same as those of 30°. This difference may be caused by inherent characteristics of adsorption to the surface of the QCM electrode.

Picogram detection of metal ions by melanin-sensitized piezoelectric sensor

A heavy metal ion sensor was constructed by cross-linking melanin onto the gold electrode of quartz crystal microbalance (QCM). A mercury ion sensitivity of 518±37Hz/ppm was observed, a substantial increase in sensitivity compared to previous reports of 10–50Hz/ppm with the limit of detection at 5ppb. Detection of other metal ions including Sn2+, Ge4+, Li+, Zn2+, Cu2+, Bi3+, Co2+, Al3+, Ni2+, Ag+, and Fe3+ were also performed. Unexpectedly, binding of Mn7+, Pb2+, Cd2+, and Cr3+ increased resonant frequencies. The surface profile of melanin thin film upon binding to metal ions was investigated by atomic force microscopy (AFM). Structural change of melanin upon binding to metal ions was characterized by circular dichroism and by infrared spectroscopy. The current study provides the first example of melanin-coated piezoelectric sensor showing high sensitivity and selectivity to metal ions.

Highly Sensitive Biomolecule Detection on a Quartz Crystal Microbalance Using Gold Nanoparticles as Signal Amplification Probes

We report here a novel strategy for the high-sensitive detection of target biomolecules with very low concentrations on a quartz crystal microbalance (QCM) device using gold nanoparticles as signal enhancement probes. By employing a streptavidin-biotin interaction as a model system, we could prepare biotin-conjugated gold nanoparticles maintaining good dispersion and long-term stability by controlling the biotin density on the surface of gold nanoparticles that have been investigated by UV-vis spectra and AFM images. These results showed that 10 microM N-(6-[biotinamido]hexyl)-3'-(2'-pyridyldithio)propionamide (biotin-HPDP) was the critical concentration to prevent the nonspecific aggregation of gold nanoparticles in this system. For sensing streptavidin target molecules by QCM, biotinylated BSA was absorbed on the Au surface of the QCM electrode and subsequent coupling of the target streptavidin to the biotin in the sensing interface followed. Amplification of the sensing process was performed by the interaction of the target streptavidin on the sensing surface with gold nanoparticles modified with 10 microM biotin-HPDP. The biotinylated gold nanoparticles were used as signal amplification probes to improve the detection limit, which was 50 ng/ml, of the streptavidin detection system without signal enhancement, and the calibration curve determined for the net frequency changes showed good linearity over a wide range from 1 ng/ml to 10 microg/ml for the quantitative streptavidin target molecule analysis. In addition, the measured dissipation changes suggested that the layer of biotin-BSA adsorbed on the Au electrode and the streptavidin layer assembled on the biotin-BSA surface were highly compact and rigid. On the other hand, the structure formed by the biotinylated gold nanoparticles on the streptavidin layer was flexible and dissipative, being elongated outward from the sensing surface.

Antibody immobilization to phospholipid polymer layer on gold substrate of quartz crystal microbalance immunosensor

To modify gold electrode for immunosensor to construct an artificial cell membrane structure, water-soluble amphiphilic phospholipid polymer, poly[2-methacryloyloxyehtyl phosphorylcholine-co-n-butyl methacrylate-co-p-nitrophenyloxycarbonyl poly(ethylene glycol) methacrylate (PMBN)] was applied. The polymer had active ester groups for immobilization of biomolecules and it was converted partially to thiol groups for binding to gold substrates. The partially thiolated PMBN was adsorbed on a gold electrode of quartz crystal microbalance (QCM). Surface characterization of adsorbed PMBN layers was thoroughly investigated with reflectance anisotropy spectroscopy, ellipsometry spectroscopy, dynamic contact angle and X-ray photoelectron spectroscopy measurements. Among several PMBN, having different degree of thiolation, it was concluded that 21.5% thiolated PMBN layer had the most well-ordered phosphorylcholine groups in its outer surface. The proteins adsorption test revealed that the phosphorylcholine group on the outer side of PMBN layers, which was substituted their active ester groups by glycine, showed suppress the non-specific adsorption of proteins, such as bovine serum albumin and γ-globulin. Also, through antigen–antibody binding evaluation, the anti-C-reactive protein antibody immobilized on the PMBN surface worked well and it was confirmed that denaturation of the antibody on the PMBN layers was hardly occurred in spite of 60 days storage at 4°C. The antibody conjugated phospholipid polymer layer with well-ordered phosphorylcholine group could be outstanding functional membrane for biomedical diagnostic devices without non-specific binding and reduction of immunologic activity of immobilized antibody.

The different self-assembled way of n- and t-dodecyl mercaptan on the surface of copper

The self-assembled monolayers (SAMs) of n- and t-dodecyl mercaptan on the surface of copper have been obtained. As evidenced by electrochemical impedance spectroscopy (EIS), two kinds of the alkanethiols can self-assemble on the copper surface. But the results of the quartz crystal microbalance (QCM) show that the self-assembled way of the two alkanethiols are different. The SAMs of n-dodecyl mercaptan can increase the weight of the QCM electrode and the SAMs of t-dodecyl mercaptan, on the contrary, make the weight of the QCM electrode decrease. Inspected with the SEM, it is found that a lot of pits spread all over the copper surface after having been modified with t-dodecyl mercaptan. All the results suggest that the self-assemble of t-dodecyl mercaptan on the copper surface can erode and dissolve copper surface sharply.

Humidity sensing properties of Pd 2+-doped ZnO nanotetrapods

Pd 2+-doped ZnO nanotetrapods were prepared and studied for the humidity detection application. The humidity sensors developed were featured by combination of a quartz crystal microbalance (QCM) as a transducer and Pd 2+-doped ZnO nanotetrapods as a sensing element. The ZnO nanotetrapods were synthesized by evaporating highly pure zinc pellets (99.999%) at 900 °C in air and PdCl 2 was doped on by traditional solution mixing process. Then the mixed solution distributed onto the electrode surfaces of the quartz crystal at room temperature. Pd 2+-doped ZnO nanotetrapods were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The experimental results indicated that the response of the sensors varied with the different dosage PdCl 2. Linear regression algorithm was used for evincing the highly linear behavior of the Pd 2+-doped ZnO nanotetrapods sensor. In this humidity sensing system, the Pd 2+-doped ZnO nanotetrapods sensing material coated on the gold electrode of QCM showed good sensitivity (∼74.24324 Hz/%RH (relative humidity)), reproducibility, linearity ( R 2 = −0.98834), short response and recovery time (less than 5 s).

Nucleation-growth process of scale electrodeposition—Influence of the mass transport

An impinging jet cell was used to investigate the influence of the convection on the kinetics of scale deposition in a carbonically pure water. CaCO3 crystallized due to the increase of the local pH obtained by the reduction of dissolved oxygen. The working electrode was the transparent electrode of an electrochemical quartz crystal microbalance which records versus time the mass of the deposit and the microscope image of the electrode/solution interface. The chronoelectrogravimetric curves showed that the rate of the CaCO3 deposition increased with the convection until a limiting value of the Reynolds number Re while the current of oxygen reduction continues to increase following a Re1/2 law. This result was confirmed by the measurement of the growth rate of the two CaCO3 crystal forms obtained by using the optical method. On the contrary, the nucleation rate was not influenced by the flow rate. It was shown that the kinetics of scale deposition was directly linked to the interfacial pH; a theoretical approach gives the interfacial pH with respect to the Re number.

EQCM and Fluoroelectrochemical Studies on the Catalytic Oxidation of NADH at a Pencil 8B‐Scrawled Gold Electrode with High Detection Sensitivity

AbstractWe report for the first time the effective catalytic electrooxidation of nicotinamide adenine dinucleotide (NADH) on the pencil 8B‐scrawled gold electrode of an electrochemical quartz crystal microbalance (EQCM). The EQCM allowed us to quantitatively evaluate the catalytic activity of the pencil‐scrawled Au electrode. With increasing the mass of modified pencil powders, the peak potential for NADH oxidation shifted negatively, with maximum shift of −0.35 V at saturated pencil modification; the NADH‐oxidation peak current density (jp) was also notably increased, and the jp at saturated pencil modification was found to be larger than those at conventional pencil 8B and bare Au electrodes. Sensitive amperometric detection of NADH was achieved at the gold electrode with saturated pencil modification, with low detection potential (0.4 V versus SCE), low detection limit (0.08 μmol L−1) and wide linear range (0.2–710 μmol L−1). The fluoroelectrochemical measurements of NADH at bare and pencil‐modified gold electrodes were also conducted with satisfactory results. The convenient and low‐cost modification of pencil powders on the Au electrode may have presented a new functional surface of the EQCM, which is recommended for wider applications to bioelectrochemical studies, especially in view of the EQCM's capability of providing abundant in situ information in relevant processes.

Long-term monitoring of biofilm growth and disinfection using a quartz crystal microbalance and reflectance measurements

A biofilm reactor was constructed to monitor the long-term growth and removal of biofilms as monitored by the use of a quartz crystal microbalance (QCM) and a novel optical method. The optical method measures the reflectance of white light off the surface of the quartz crystal microbalance electrode (gold) for determination of the biofilm thickness. Biofilm growth of Pseudomonas aeruginosa (PA) on the surface was used as a model system. Bioreactors were monitored for over 6 days. Expressing the QCM data as the ratio of changes in resistance to changes in frequency (Δ R/Δ f) facilitated the comparison of individual biofilm reactor runs. The various stages of biofilm growth and adaptation to low nutrients showed consistent characteristic changes in the Δ R/Δ f ratio, a parameter that reflects changes in the viscoelastic properties of the biofilm. The utility of white light reflectance for thickness measurements was shown for those stages of biofilm growth when the solution was not turbid due to high numbers of unattached cells. The thickness of the biofilms after 6 days ranged from 48 μm to 68 μm. Removal of the biofilm by a disinfectant (chlorine) was also measured in real time. The combination of QCM and reflectance allowed us to monitor in real time changes in the viscoelastic properties and thickness of biofilms over long periods of time.

Shear moduli of anion and cation exchanging polypyrrole films

By using the acoustic impedance method, storage (G′) and loss moduli (G″) have been determined for poly(pyrrole) films grown on the gold electrode of an electrochemical quartz crystal microbalance from aqueous LiClO4 and sodium tosylate solutions. At 10 MHz, for 0.3–0.4 μm films G′ = 6 × 106, G″ = 2 × 106 dyn/cm2 for perchlorate and 2.5 × 108 and 1.1 × 108 dyn/cm2 for tosylate ions were determined. Cycling in the corresponding monomer free solutions did not significantly change the properties of the perchlorate anion film, but decreased the moduli of the tosylate films to 6–8 × 107 dyn/cm2. A slight increase of G during oxidation has been observed, i.e., the films are more stiff in the oxidized state.

A Study of Gypsum Scale Formation using Quartz Crystal Microbalance

AbstractThe quartz crystal microbalance (QCM) has been used extensively as a mass sensor due to its extremely high sensitivity to small mass loadings. Conventional measurement of the amount of scale deposited on a surface is restricted by the sensitivity limit of analytical balances. Thefirst attempt to investigate the deposition of gypsum scale on a surface using a rotating electrochemical QCMsystem was carried out to investigate the eflects of many factors at the early stages of scale formation. Results indicated there was almost no induction time for this system, and the long induction time observed in the conventional system was due to the limited sensitivity of the analytical balance. A slow increase in scale amount was observed at the beginning of the scaling process as shown by the plot offrequency or mass change against time. After this period the curve rises steeply and becomes almost linear. The supersaturation level of the solutions and the rotating speed have significant effects on the gypsum scaling.A QCM flow‐cell system has also been developed to investigate the scaling of gypsum on the pipe wall. This system is similar to a conventional pipe flow system except that its size is much smaller and the deposition of scales can be monitored with the QCM electrode throughout the scaling process. The mass change is plotted against time and results are compared for the rotating QCM system and the conventional system. It is noticed that the formation of gypsum on the QCM electrode is greatly dependent on both the supersaturation of the solution and the flow rate of the fluid passing through the flow cell.

A low humidity sensor made of quartz crystal microbalance coated with multi-walled carbon nanotubes/Nafion composite material films

A low humidity sensor was made of a quartz crystal microbalance (QCM) coated with multi-walled carbon nanotubes/Nafion (MWCNTs/Nafion) composite material films. The microstructure of the MWCNTs/Nafion composite material films showed strong interaction between MWCNTs and Nafion. The MWCNTs/Nafion composite material films coated on the gold electrode of QCM showed excellent sensitivity (3.56 −ΔHz/Δppmv at 23.4ppmv), linearity (R2=0.9604) and short response time (23s at 83.5ppmv). The water vapor molecules adsorbed onto the MWCNTs/Nafion films showed higher frequency shift than Nafion and single-walled carbon nanotubes/Nafion (SWCNTs/Nafion) films. The adsorption dynamic analysis, molecular mechanics calculation (association constant), was used to elucidate the effect of adding SWCNTs and MWCNTs into Nafion on the increased sensitivity of low humidity sensing.

The fungal hydrophobin RolA recruits polyesterase and laterally moves on hydrophobic surfaces

When fungi grow on plant or insect surfaces coated with wax polyesters that protect against pathogens, the fungi generally form aerial hyphae to contact the surfaces. Aerial structures such as hyphae and conidiophores are coated with hydrophobins, which are surface-active proteins involved in adhesion to hydrophobic surfaces. When the industrial fungus Aspergillus oryzae was cultivated in a liquid medium containing the biodegradable polyester polybutylene succinate-coadipate (PBSA), the rolA gene encoding hydrophobin RolA was highly transcribed. High levels of RolA and its localization on the cell surface in the presence of PBSA were confirmed by immunostaining. Under these conditions, A. oryzae simultaneously produced the cutinase CutL1, which hydrolyses PBSA. Pre-incubation of PBSA with RolA stimulated PBSA degradation by CutL1, suggesting that RolA bound to the PBSA surface was required for the stimulation. Immunostaining revealed that PBSA films coated with RolA specifically adsorbed CutL1. Quartz crystal microbalance analyses further demonstrated that RolA attached to a hydrophobic sensor chip specifically adsorbed CutL1. Circular dichroism spectra of soluble-state RolA and bound RolA suggested that RolA underwent a conformational change after its adsorption to hydrophobic surfaces. These results suggest that RolA adsorbed to the hydrophobic surface of PBSA recruits CutL1, resulting in condensation of CutL1 on the PBSA surface and consequent stimulation of PBSA hydrolysis. A fluorescence recovery after photobleaching experiment on PBSA films coated with FITC-labelled RolA suggested that RolA moves laterally on the film. We discuss the novel molecular functions of RolA with regard to plastic degradation.

Quartz crystal microbalance (QCM) sensor for CH 3SH gas by using polyelectrolyte-coated sol–gel film

A new structure of sensing film for QCM sensor electrode was investigated. Gas-sensing device for toxic gases requires high sensor sensitivity and quick response. Increasing the surface area of sensing film was effective to improve the sensor sensitivity and response speed of QCM sensors, however it is difficult to increase the surface area of polymeric film. In this paper, Al 2O 3 porous film was coated on QCM substrate by sol–gel method between the QCM electrode and polymeric layer in order to increase the surface area of polymeric layer. By using this manner, polymeric sensing films with high porosity can be fabricated without high-temperature treatment. The sensor was evaluated for the detection of methyl mercaptan (CH 3SH) by using poly(ethylene imine) (PEI) as polymeric layer. The sensor with Al 2O 3 porous layer showed high sensitivity and quick response rather than the sensor without the inorganic layer. The Al 2O 3 layer worked for increasing the surface area of polyelectrolyte layer which resulted in the increasing of the sensor sensitivity.

Size-selective recognition of catecholamines by molecular imprinting on silica–alumina gel

The preparation of a catecholamine receptor was carried out using a molecular imprinting method with silica-alumina gel to form complementary structures for template recognition. The molecularly imprinted polymer (MIP) was synthesized by the condensation of silicate from tetraethyl orthosilictate (TEOS) under hydrothermal conditions at 60 degrees C. Aluminum chloride was added as a functional monomer to increase the material's rebinding ability. The selectivity of the MIP receptor prepared with different ratios of template to Si and Al, was examined with seven analytes including: dopamine, epinephrine, norepinephrine, ascorbic acid, homovanillic acid, uric acid, and l-tyrosine. The results showed a size selective effect for the receptors with respect to the recognition of the catecholamines. Some factors affecting the recognition ability were investigated including: the solution pH of analytes, surface capping on the MIP, and the imprinting pH of the silica-alumina solution. Also, the catecholamine MIP films on quartz crystal microbalance (QCM) electrodes were fabricated as sensors for in situ monitoring of the analytes in a 2-propanol solution.

Kinetic Studies of DNA Cleavage Reactions Catalyzed by an ATP-Dependent Deoxyribonuclease on a 27-MHz Quartz-Crystal Microbalance

Catalytic DNA cleavage reactions by an ATP-dependent deoxyribonuclease (DNase) from Micrococcus luteus were monitored directly with a DNA-immobilized 27-MHz quartz-crystal microbalance (QCM). The 27-MHz QCM is a very sensitive mass-measuring device in aqueous solution, as the frequency decreases linearly with increasing mass on the electrode at a nanogram level. Three steps in ATP-dependent DNA hydrolysis reactions, including (1) binding of DNase to the end of double-stranded DNA (dsDNA) on the QCM electrode (mass increase), (2) degradation of one strand of dsDNA in the 3' --> 5' direction depending on ATP (mass decrease), and (3) release of the enzyme from the nonhydrolyzed 5'-free-ssDNA (mass decrease), could be monitored stepwise from the time dependencies of QCM frequency changes. Kinetic parameters for each step were obtained as follows. The binding constant (K(a)) of DNase to the dsDNA was determined as (28 +/- 2) x 10(6) M(-)(1) (k(on) = (8.0 +/- 0.3) x 10(3) M (-)(1) s(-)(1) and k(off) = (0.29 +/-0.01) x 10(-)(3) s(-)(1)), and it decreased to (0.79 +/- 0.16) x 10(6) M(-)(1) (k'(on) = (2.3 +/- 0.2) x 10(3) M (-)(1) s(-)(1) and k'(off) = (2.9 +/- 0.1) x 10(-)(3) s(-)(1)) for the completely nonhydrolyzed 5'-free ssDNA. This is the reason the DNase bound to the dsDNA substrate can easily release from the nonhydrolyzed 5'-free-ssDNA after the complete hydrolysis of the 3' --> 5' direction of the complementary ssDNA. K(a) values depended on the DNA structures on the QCM, and the order of these values was as follows: the dsDNA having a 4-base-mismatched base-pair end (3) > the dsDNA having a 5' 15-base overhanging end (2) > the dsDNA having a blunt end (1) > the ssDNA having a 3'-free end (4) >> the ssDNA having a 5'-free end (5). Thus, DNase hardly recognized the free 5' end of ssDNA. Michaelis-Menten parameters (K(m) for ATP and k(cat)) of the hydrolysis process also could be obtained, and the order of k(cat)/K(m) was as follows: the dsDNA having a blunt end (1) approximately the dsDNA having a 4-base-mismatched base-pair end (3) > the ssDNA having a free 3' end (4) >> the ssDNA having a free 5' end (5). Thus, DNase could not recognize and not hydrolyze the free 5' end of ssDNA. The DNA hydrolysis reaction could be driven by dATP and GTP (purine base) as well as ATP, whereas the cleavage efficiency was very low driven with UTP, CTP (pyrimidine base), ADP, and AMP.