Biofouling of dextran-derivative layers investigated by quartz crystal microbalance

This study reports the fouling of carboxymethyl dextran (CMD) layers in cell culture medium, fibronectin, and serum solutions. CMD layers were covalently immobilized onto amine groups available either on an n-heptylamine plasma polymer (HApp) layer or onto a polyethylenimine (PEI) coating grafted to an acetaldehyde plasma polymer (AApp) layer. The successful immobilization of the graft layers was demonstrated by X-ray photoelectron spectroscopy (XPS). Primary amines on HApp and AApp + PEI surfaces were quantified using a colorimetric assay. Quartz crystal microbalance (QCM) was used to investigate in real-time the fouling of the graft layers upon incubation in cell culture medium (RPMI), fibronectin, and foetal bovine serum (FBS) solutions. HApp, AApp and AApp + PEI layers exhibited large fouling in fibronectin and FBS solutions, while fouling in RPMI cell culture medium was not significant. Protein repellent properties of CMD layers in FBS and fibronectin have been demonstrated compared to the other tested surfaces. QCM has shown that both CMD layers were fouled to a small extent in RPMI medium.     

Chemical oscillation induced periodic swelling and shrinking of a polymeric multilayer investigated with a quartz crystal microbalance

Poly(acrylic acid- co-3-azidopropyl acrylate) and poly(acrylic acid- co-propargyl acrylate) have been alternately fabricated into a multilayer via the click reaction. The layer-by-layer deposition was monitored with a quartz crystal microbalance with dissipation (QCM-D) in real time. The response of the multilayer under continuous flow of a bromate-sulfite-ferrocyanide solution with pH oscillation has also been investigated by use of QCM-D. As the pH oscillates between 3.1 and 6.6, either the frequency shift (Delta f) or the dissipation shift (Delta D) periodically varies with a constant amplitude, clearly indicating that the multilayer swells and shrinks oscillatedly. The changes of thickness, shear viscosity, and elastic shear modulus further indicate the oscillation.     

Adsorption of liposomes and emulsions studied with a quartz crystal microbalance

The adsorption from phospholipid liposome solutions (1.2%) and phospholipid stabilized oil-in-water emulsions (20% purified soybean oil) with the same phospholipid liposome concentration, has been followed by means of a quartz crystal microbalance allowing the simultaneous determination of changes in resonance frequency and energy dissipation. Both the fundamental resonance frequency and the third overtone were used for following the interfacial processes. The adsorption from the liposome solution resulted in formation of a phospholipid bilayer with an additional and incomplete outer layer of liposomes. The outer layer was removed by dilution leaving a bilayer of phospholipids on the surface. The adsorption process observed from the concentrated emulsion solution was considerably more complex. A slow spreading process that also resulted in some expulsion of material from the interface followed the rapid initial adsorption of emulsion droplets. After rinsing with water a phospholipid bilayer was retained on the surface.     

Adsorption kinetics of an engineered gold binding Peptide by surface plasmon resonance spectroscopy and a quartz crystal microbalance

The adsorption kinetics of an engineered gold binding peptide on gold surface was studied by using both quartz crystal microbalance (QCM) and surface plasmon resonance (SPR) spectroscopy systems. The gold binding peptide was originally selected as a 14-amino acid sequence by cell surface display and then engineered to have a 3-repeat form (3R-GBP1) with improved binding characteristics. Both sets of adsorption data for 3R-GBP1 were fit to Langmuir models to extract kinetics and thermodynamics parameters. In SPR, the adsorption onto the surface shows a biexponential behavior and this is explained as the effect of bimodal surface topology of the polycrystalline gold substrate on 3R-GBP1 binding. Depending on the concentration of the peptide, a preferential adsorption on the surface takes place with different energy levels. The kinetic parameters (e.g., K(eq) approximately 10(7) M(-1)) and the binding energy (approximately -8.0 kcal/mol) are comparable to synthetic-based self-assembled monolayers. The results demonstrate the potential utilization of genetically engineered inorganic surface-specific peptides as molecular substrates due to their binding specificity, stability, and functionality in an aqueous-based environment.     

Immunodetection by quartz crystal microbalance

Biodetection is one of the most important challenges for the twenty-first century: many fields are concerned, mainly environmental and medical. The quartz crystal microbalance (QCM) may offer great possibilities for this purpose: a direct response signal, which characterizes the binding event between a sensitive layer, immobilized onto the surface transducer, and the analyte to be detected, can be obtained. However, for the detection of small biomolecules such as antigens, it is quite difficult to obtain an observable signal that corresponds directly to the binding event. In general, this is owing to the lack of mass sensitivity of the commonly used QCM, with 5- to 10-MHz quartz crystals. For improving this mass sensitivity, a 27-MHz quartz resonator was developed and incorporated in a flow-through microcell. Two biospecies, IgG rabbit and peroxidase enzyme, were studied with this ultra-sensitive QCM in terms of specificity, detection limit, and calibration curve.     

Dynamic interaction between melamine and cyanuric acid in artificial urine investigated by quartz crystal microbalance

The dynamic interaction between melamine (M) and cyanuric acid (CA) in artificial urine was investigated by a flow injection analysis-quartz crystal microbalance (FIA-QCM) system. Melamine was used as the recognition element and immobilized onto the QCM gold surface. The process of M and CA interaction was recorded by FIA-QCM in real-time. The multilayer complex of M and CA was successfully formed on the crystal surface of the QCM when CA and M were introduced into the FIA-QCM system alternately. The influence of pH on the M and CA interaction indicated that the M-CA multilayer complex possesses high stability over a wide range of pH values, especially in physiological urine condition. The association and dissociation rate constants were determined under artificial urine condition and the association constant for M and CA was calculated as 10(2) L mol(-1). The M-CA complex was further characterized by Fourier transform infrared spectroscopy (FT-IR) and atomic force microscopy (AFM). Mechanism study suggested that the formation of the multilayer complex in artificial urine was mainly attributed to the intermolecular hydrogen bonding between M and CA. The work provides direct insight into the dynamic interaction between M and CA under physiological conditions and would be helpful for the research of kidney stones induced by melamine contamination.     

Adsorption of bituminous components at oil/water interfaces investigated by quartz crystal microbalance: implications to the stability of water-in-oil emulsions

Silica-gel-coated QCM crystals oscillating in a thickness shear mode are used to measure adsorption of bituminous components in water-saturated heptol (1/1 vol ratio of a heptane/toluene mixture) at the oil/water interface. In addition to the viscoelasticity of the adsorbed film, the effects of the bulk liquid density and viscosity as well as the liquid trapped in interfacial cavities are taken into account for the calculation of adsorbed mass. Asphaltenes in heptol adsorb continuously at the oil/water interface, while resins (the surface-active species in maltenes) show adsorption saturation in the same solvent. For Athabasca bitumen in heptol, two adsorption regimes are observed depending on concentration. At low concentrations, a slow, non-steady-state, and irreversible adsorption takes place. At high concentrations, a steady-state adsorption with limited reversibility results in a quick adsorption saturation. The threshold concentration between these adsorption regimes is 1.5 wt % and 8 wt % for oil/water and oil/gold interfaces, respectively. The threshold concentration, the total adsorbed amount, and the flux of non-steady-state adsorption depend on the resin-to-asphaltene ratio. The threshold concentration is related to the earlier reported critical bitumen concentration characterizing the rigid-to-flexible transition of the interfacial film. We propose a new mechanism based on the change of the effective resin-to-asphaltene ratio with dilution to explain both the adsorption behavior and emulsion stability.     

Ion and water transports in Prussian blue films investigated with electrochemical quartz crystal microbalance

Water and ion transport in electrochemically prepared Prussian blue (PB, Iron(III) hexacyanoferrate(II)) films has been investigated with the electrochemical quartz crystal microbalance (EQCM) and the electrochemical/electrogravimetric impedance techniques. It is shown that the freshly prepared PB film is highly hydrated and that it undergoes an irreversible mass change during the first cathodic scan. The latter result supports the previously proposed structural reorganization scheme of the PB film from the insoluble form Fe₄[Fe(CN)₆]₃·6H₂O to the soluble form MFeFe(CN)₆ (M is a monovalent cation). It is also shown that, during the first cathodic scan, a substantial amount of water is excluded from the PB film. After the structural reorganization, ion transport during the redox reaction of the PB film is cation-dominant with a small fraction of accompanying water transport.     

Reentrant behavior of grafted poly(sodium styrenesulfonate) chains investigated with a quartz crystal microbalance

Poly(sodium styrenesulfonate) (PSSNa) chains have been grafted onto a SiO(2)-coated resonator surface. The conformational changes of grafted chains have been investigated using a quartz crystal microbalance with dissipation (QCM-D) in the presence of monovalent or multivalent salts as a function of ionic strength. In the case of monovalent counterions, the changes in frequency (Δf) and dissipation (ΔD) indicate that the highly extended PSSNa chains first shrink into a loose and inhomogeneous layer as the ionic strength increases. As the ionic strength increases further, the chains will collapse and form a denser and more homogeneous layer. In the case of divalent or trivalent counterions, the grafted PSSNa chains also collapse into a dense layer as the ionic strength increases. However, when the ionic strength is above a critical value, the chains would re-expand so that the layer becomes partially extended due to the charge inversion. Additionally, the effect of ion-specificity on the conformational changes of the chains has also been examined.     

Human immunoglobulin adsorption investigated by means of quartz crystal microbalance dissipation, atomic force microscopy, surface acoustic wave, and surface plasmon resonance techniques

Time-resolved adsorption behavior of a human immunoglobin G (hIgG) protein on a hydrophobized gold surface is investigated using multitechniques: quartz crystal microbalance/dissipation (QCM-D) technique; combined surface plasmon resonance (SPR) and Love mode surface acoustic wave (SAW) technique; combined QCM-D and atomic force microscopy (AFM) technique. The adsorbed hIgG forms interfacial structures varying in organization from a submonolayer to a multilayer. An "end-on" IgG orientation in the monolayer film, associated with the surface coverage results, does not corroborate with the effective protein thickness determined from SPR/SAW measurements. This inconsistence is interpreted by a deformation effect induced by conformation change. This conformation change is confirmed by QCM-D measurement. Combined SPR/SAW measurements suggest that the adsorbed protein barely contains water after extended contact with the hydrophobic surface. This limited interfacial hydration also contributed to a continuous conformation change in the adsorbed protein layer. The viscoelastic variation associated with interfacial conformation changes induces about 1.5 times overestimation of the mass uptake in the QCM-D measurements. The merit of combined multitechnique measurements is demonstrated.     

石英晶体微天平的新进展

石英晶体微天平（quartz crystal microbalance,QCM）是一种对界面变化敏感的仪器,它已经在物理、化学、生物学、药物学、临床医学、环境科学等学科的界面问题研究中得到了一定的应用.然而,QCM在液相下的应用和推广一直受限于QCM数据定量解释的困难.为此,科研工作者发展了多种高级的QCM,比如带阻抗分析功能的QCM（impedance QCM,i-QCM）或带能量耗散监测功能的QCM（QCM with dissipation,QCM-D）,同时还发展了许多相应的理论模型.但是,对于多数生物、化学工作者来说,这些理论过于复杂.这极大地限制了QCM的推广和潜力发挥.本文以我们小组在QCM方面的研究工作为线索,对已报道的分析方法、模型和方程按5类应用条件进行了整理,给出了明确的界定标准：它们是：1,固-气界面;2,牛顿流体;3,固-液界面的薄膜;4,固-液界面厚膜;5,固-液界面超厚膜.对于每一类情况,我们将用通俗易懂的语言描述如何对QCM数据进行简化却又保证研究精度需要的定量分析.对于液态环境下的QCM数据的分析,我们着重介绍了＂固化水层＂模型,该模型允许QCM在一定的条件下成为一把＂分子尺＂,工作范围从几个纳米到数百纳米.该分子尺在多个创新界面问题研究中得到很好的应用.最后,我们从理论上分析了QCM作为生物传感器的先天缺陷--因基于面均质量检测的原理,QCM技术对溶液中蛋白的检测下限仅在1μg mL-1数量级.进一步,我们探索了QCM的发展方向和潜在应用领域,希望籍此能进一步推广QCM在各个学科界面问题中的研究应用.     

Lectin-carbohydrate affinity measured using a quartz crystal microbalance

The association of two molecules is described by two parameters, association equilibrium and association rate constants, which are characteristic for a given type of interaction. Usually, they are determined for interacting molecules dissolved in solution. However, for many applications one type of molecules is immobilized on a substrate, which may influence the binding kinetics. The studied complex of concanavalin A and carboxypeptidase Y belongs to the lectin-carbohydrate type of interaction involving the recognition of oligosaccharide moieties. The concanavalin A was immobilized on a gold electrode of quartz crystal, while carboxypeptidase Y was added to a buffer (Tris-buffered saline). The constants describing the association of the investigated molecules were determined on the basis of measurements performed using a quartz crystal microbalance in liquid. The obtained values were (0.59+/-0.01)x10(6) M(-1) for the association equilibrium constant and (5.6+/-0.1)x10(4) M(-1)s(-1) for the association rate constant. The saturation binding experiment gave another value of the association constant, (2.7+/-0.02)x10(6) M(-1). The comparison of obtained values with previously published ones verifies that the molecule orientation and binding site accessibility for specific ligands could influence the association equilibrium constant value. The presented measurements demonstrate the ability of a quartz crystal microbalance to detect and to evaluate the association process occurring between molecules.     

Frequency response of a quartz crystal microbalance loaded by liquid drops

The frequency response of a quartz crystal microbalance (QCM) in contact with a spreading liquid drop is studied in this paper. An improved model describing the frequency change of the QCM with the shape evolution of the liquid drop with time is proposed based on hydrodynamic analysis, which has not been reported in the literature. It is found that the drop spreading shape, including the base radius and height, has a significant influence on the frequency response of the QCM, resulting in an unexpected increase in the resonant frequency of the QCM. The model shows that the combination of the knowledge about the radial sensitivity of the QCM and the dynamic spreading of the liquid drop is potentially important to optimize the interpretation of the experimental results. The predicted results are verified with experimental results obtained with silicone oil.     

Reentrant behavior of poly(N-isopropylacrylamide) brushes in water-methanol mixtures investigated with a quartz crystal microbalance

The solvent composition induced reentrant behavior of poly(N-isopropylacrylamide) (PNIPAM) chains grafted on a SiO2 surface in water-methanol mixtures was investigated using a quartz crystal microbalance with dissipation monitoring (QCM-D) at 20 degrees C. The frequency and energy dissipation responses showed that the grafted PNIPAM chains sharply collapse when the methanol content (x(m)) reaches approximately 17 mol %. In the range 17-50 mol %, the grafted chains remain in a collapsed state. Further increase of the methanol content leads to an abrupt reswelling of the collapsed chains at x(m) > approximately 50 mol %. The sharp reentrant swelling-to-collapse-to-swelling transition was attributed to the water-methanol complexation instead of the preferential adsorption effect. Our results also suggest that the water-methanol complexation is not induced by hydrophobic interaction but by hydrogen bonding.     

A quartz crystal microbalance study on a metallic nickel electrode

Electrochemical processes taking place on a Ni electrode have been investigated with the electrochemical quartz crystal microbalance. At potentials negative of ca. –500 mV vs. SCE, a closed frequency loop is observed without irreversible changes in the mass of the electrode. The phase transition - -Ni(OH)₂, taking place at potentials positive to –500 mV vs. SCE, is accompanied by an irreversible increase in the mass of the electrode. When Ni(OH)₂ is further oxidized, the frequency increase is followed by a decrease, indicating the transport of various species in both directions, i.e. from and into the electrode. During the Ni(OH)₂ oxidation reaction the transport of species responsible for the mass increase is slower than the charge transfer process.Contribution to the 3rd Baltic Conference on Electrochemistry, GDASK-SOBIESZEWO, 23–26 April 2003. Dedicated to the memory of Harry B. Mark, Jr. (February 28, 1934–March 3rd, 2003)     

The quantification of potassium using a quartz crystal microbalance

N,N'-dibenzyl-4,13-diaza-18-crown-6 (A) and bis[(benzo-15-crown-5)-4'-ylmethyl] pimelate (B) were tested as coatings for two piezoelectric crystals for potassium quantification. Both sensors showed stability, reversibility and sensitivity characteristics that allowed their use in quantitative analysis. However, compound A is much more sensitive to potassium than B. Compound A also shows a larger relative sensitivity for potassium with regard to sodium than B. A pharmaceutical sample of known composition was analysed both by an acoustic wave sensor with a crystal coated with compound A and by conductivity. No statistically significant difference in the median of the results was found (alpha = 0.05), although precision is superior for the conductivity methodology. Performance of the sensor in terms of frequency stability and selectivity was improved by the incorporation of PVC, a plasticizer and a lipophilic salt in the coating composition. Limits of detection found for potassium were 1.92 ppm, or 1.75 ppm for a crystal with a frequency decrease due to coating of 2.9 kHz or 3.9 kHz, respectively. Selectivity coefficients (fixed interference 80 ppm) for potassium over Na, Ca, Al, Zn, Mg, and Fe ranged from 0.103 to 0.332.     

Dual quartz crystal microbalance compensation using a submerged reference crystal. Effect of surface roughness and liquid properties

Absolute resonant frequency measurements were made on gold-coated AT-cut quartz crystals with one face in contact with a series of liquids. The effect of surface roughness and liquid properties (viscosity and density) was analyzed in terms of a “trapped liquid” model. In this model, liquid present in surface imperfections is viewed as rigidly coupled mass. In some of the literature this density-dependent, but not viscosity-dependent, term is viewed as being additive to the hydrodynamic shift seen for a smooth surface. Data obtained using 1 μm and 5 μm surface finish crystals are inconsistent with the predictions of the trapped liquid model. This suggests hydrodynamic coupling between liquid internal and external to the crevices. Despite the lack of a theoretical model for the liquid motion, it is possible to compensate for frequency variations resulting from changing liquid properties and for roughness effects by making direct measurements of the resonant frequency difference between two crystals exposed to the same solution. This novel procedure works to the extent that the two crystals have similar surface topographies. Compensation is excellent for 1 μm finish crystals and good for 5 μm finish crystals.     

Development of a sensor for calcium based on quartz crystal microbalance

A new sensor for calcium based on a piezoelectric quartz crystal is presented. The selectivity depends on the ratio lipophilic salt/ionophore of the composition of the coating of the quartz crystal. A crystal coated with a THF solution of PVC (34.5% w/w), DOS (62.1% w/w) and 10,19-bis[(octadecylcarbamoyl) methoxyacetyl]-1,4,7,13,16-pentaoxa-10,19-diaza cycloheneicosane (3.4% w/w) and a salt/ionophore molar proportion of 60%, corresponding to a frequency decrease of the dry crystal of 6.0 kHz, showed a detection limit to calcium of 2.2 mg/L. Both a standard calcium chloride solution and a commercially balanced salt solution for tissue culture were analyzed subsequent to ion chromatographic separation. The results obtained with the sensor developed were compared with those obtained with a conductivity detector. Although the results from both detectors agreed for the standard solution, only the quartz crystal sensor was able to give reliable results for the tissue culture solution.     

Development of a sensor for calcium based on quartz crystal microbalance

A new sensor for calcium based on a piezoelectric quartz crystal is presented. The selectivity depends on the ratio lipophilic salt/ionophore of the composition of the coating of the quartz crystal. A crystal coated with a THF solution of PVC (34.5% w/w), DOS (62.1% w/w) and 10,19-bis[(octadecylcarbamoyl) methoxyacetyl]-1,4,7,13,16-pentaoxa-10,19-diaza cycloheneicosane (3.4% w/w) and a salt/ionophore molar proportion of 60%, corresponding to a frequency decrease of the dry crystal of 6.0 kHz, showed a detection limit to calcium of 2.2 mg/L. Both a standard calcium chloride solution and a commercially balanced salt solution for tissue culture were analyzed subsequent to ion chromatographic separation. The results obtained with the sensor developed were compared with those obtained with a conductivity detector. Although the results from both detectors agreed for the standard solution, only the quartz crystal sensor was able to give reliable results for the tissue culture solution.