Rapid detection of Escherichia coliform with a bulk acoustic wave sensor based on the gelation of Tachypleus amebocyte lysate

A new sensing method (BAW-TAL technique), which combined the bulk acoustic wave (BAW) technique with the gelation reaction of Tachypleus amebocyte lysate (TAL), was used for viscosity and density measurement and applied to the detection of Escherichia coliform (E. coli). This method depended on the fact that the viscosity and density of the mixture increased, and as a result, the resonance frequency decreased correspondingly after TAL was mixed with the heated E. coli solution that contained endotoxin. Results showed that the frequency shift was linearly related to the logarithm of E. coli concentration in the range of 2.7x10(4)-2.7x10(8) cells/ml. The correlation coefficient was 0.996. This BAW-TAL method was compared with the standard pour plate counts (PPC) method. The proposed method was much more rapid and simpler for detection of E. coli than the traditional methods.     

Quartz-crystal gelation detector for the determination of fibrinogen concentration

A quartz crystal resonator was used for gelation monitoring and applied to the determination of fibrinogen concentration. The system consists of a 9-MHz AT-cut quartz crystal with a well- type cell, oscillator, frequency counter and microcomputer. The gelation time of fibrinogen on mixing with thrombin solution was determined by computer processing. The effect of temperature was avoided by the addition of aluminium oxide particles to the thrombin solution. The gelation time obtained in this system showed good linearity with fibrinogen concentration over the range 50–500 mg d l^?1.     

电化学石英晶体阻抗系统研究金电极上Fe(CN)_6~(3-)/Fe(CN)_6~(4-)电化学过程

电化学过程的石英晶体阻抗分析法已用于现场获取电活性聚合物粘弹性等信息［１,２］．本文联用ＨＰ４３９５Ａ阻抗／网络／频谱分析仪和ＥＧ＆ＧＭ２８３恒电位仪开发出电化学石英晶体阻抗系统（ＥｌｅｃｔｒｏｃｈｅｍｉｃａｌＱｕａｒｔｚＣｒｙｓｔａｌＩｍｐｅｄａｎ...     

Action mechanism of water soluble ethanol on phospholipid monolayers using a quartz crystal oscillator

Interaction between phospholipid monolayers (dihexadecyl phosphate: DHP, dipalmitoyl phosphatidyl choline: DPPC) and water soluble ethanol has been studied using quartz crystal microbalance (QCM) method and quartz crystal impedance (QCI) method. The quartz crystal oscillator was attached horizontally on the DHP and DPPC monolayers that were formed on the water surface. At low concentration, increased ethanol concentration decreased the frequency for QCM and increased the resistance for QCI. Both frequency and resistance approached asymptotically to a saturation value. A further increase in ethanol concentration induced a sudden and discontinuous linear change (a decrease in frequency and an increase in resistance). Based on these results, we propose the following action mechanism of ethanol on phospholipid monolayers: at low concentration, the ethanol hydrates adsorb into the monolayer/water interface and saturate on the interface. The monolayer viscosity also increases with the adsorption of hydrates. A further increase in concentration causes multilayer formation of hydrates and/or penetration of hydrates into the monolayer core. The viscosity of the interfacial layer (monolayer and interfacial structured water) changes dramatically according to the action of ethanol hydrates.     

Rate equation of gelation of chromium(III)-polyacrylamide sol

During gelation, the time dependence of the apparent viscosity has been used to analyze the kinetics of the gelation of polyacrylamide (PA) sol with chromium (III) ions. The investigations have stablished the following facts: Before gelation the relation between the viscosity, η, of Cr(III)-PA sol and the PA concentration is η = f([PA]) = 2.36×10¹⁵ [PA]^3.15 and the rate equation of gelation in the steady-state stage during gelation is expressed as V_n = k_s f([PA]) [PA]² [Cr(III)]².     

QCM/HCC as a platform for detecting the binding of warfarin to an immobilized film of human serum albumin

Quartz crystal microbalance/heat conduction calorimetry (QCM/HCC) is a new measurement technology that has been used to monitor simultaneously the mass and motional resistance of a thin film in conjunction with the heat flow produced by a chemical change in the film initiated by reaction with a gas. In this work we examine the applicability of the QCM/HCC in detecting chemical changes at the solution/thin film interface. Human serum albumin (HSA) was bound to the gold electrode of a 5 MHz AT-cut quartz resonator using three types of linkers and then exposed to buffered solutions of the anticoagulant drug warfarin. Changes in resonator frequency and motional resistance as well as changes in heat flow produced by warfarin binding to HSA were monitored as a function of the warfarin concentration. Differences in frequency and motional resistance changes depend upon the linker and vary both in magnitude and sign, whereas the integrated heat signal is proportional to the concentration of warfarin and independent of the linker chemistry. Quartz crystal microbalance/heat conduction calorimetry can thus be a useful tool for studying protein-ligand interactions at the solution-surface interface, even though the quartz resonator does not behave as a microbalance.     

Viscosity Behaviors of Rapidly Curable Silica Sols

The viscosity behaviors of rapidly curable transparent silica aerogels, such as time at the onset point and the slope of viscosity increase, are investigated as functions of target density, water and catalyst content. Results were compared with the visually measured gel time. The effects of temperature and shear rate on the onset point and rate of the viscosity increase are also investigated with the selected samples. Experimental design and result analysis were also conducted using the Design of Experiment (DOE) method, and the Arrhenius relation was applied to predict the temperature dependence of viscosity. It is found that the target density and catalyst content played more important roles in determining gelation and viscosity behavior than water content did. As the target density increased, the gel time and the onset point appeared at significantly earlier times and the slope increased more rapidly, while there existed an optimum catalyst and water content for fast gelation and desirable viscosity behaviors. The temperature dependence of the viscosity behaviors of rapidly curable transparent silica sols can be expressed by the Arrhenius relation. The onset time of viscosity increase was little affected by the shear rate at a low shear rate range of up to 1.32 s⁻¹, and after that it linearly decreased with increasing shear rate, while the slope of viscosity increase continuously decreased with increasing shear rate. Overall, the viscosity measurement appears as a simple and reliable method for quantitatively measuring gel time, especially for the rapidly curable sol–gel process.     

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.     

水溶性高分子弱凝胶体系凝胶化过程的Monte Carlo模拟

为研究弱凝胶的形成过程,并把高分子弱凝胶用于三次采油,采用三维Monte Carlo模拟了高分子溶液凝胶化过程. 模拟预测了凝胶化开始的时间,得到了凝胶化过程中分子量分布的演化规律和胶团生长的三维图像. 发现生成溶胶与凝胶团的歧化过程,初始聚合物的浓度对能否形成凝胶至关重要,低于临界浓度不能形成凝胶. 模拟了凝胶化速度和聚合物浓度以及交联剂浓度的关系,并与粘度随凝胶化时间变化的实验结果进行比较, 结果表明, 聚合物浓度较高时,浓度对交联反应的影响减弱,这一趋势与实验结果相一致.     

Evolution of rheological properties and local structure during gelation of siloxane-polymethylmethacrylate hybrid materials

Hybrid siloxane-polymethylmethacrylate (PMMA) nanocomposites with covalent bonds between the inorganic (siloxane) and organic (polymer) phases were prepared by the sol gel process through hydrolysis and polycondensation of 3-(trimethoxysilyl)propylmethacrylate (TMSM) and polymerization of methylmethacrylate (MMA) using benzoyl peroxide (BPO) as initiator. The effect of MMA, BPO and water contents on the viscoelastic behaviour of these materials was analysed during gelation by dynamic rheological measurements. The changes in storage (G′) and loss moduli (G′′), complex viscosity (η^*) and phase angle (δ) were measured as a function of the reaction time showing the viscous character of the sol in the initial step of gelation and its progressive transformation to an elastic gel. This study was complemented by ²⁹Si and ¹³C solid-state nuclear magnetic resonance (NMR/MAS) measurements of dried gel. The analysis of the experimental results shows that linear chains are formed in the initial step of the gelation followed by a growth of branched structures and formation of a three-dimensional network. Near the gel point this hybrid material demonstrates the typical scaling behaviour expected from percolation theory.     

Single-drop method for determination of cyanide in solution with a piezoelectric quartz crystal

The change in frequency of a horizontal quartz crystal in contact with a single drop of solution is measured. When the gold electrode of the crystal is dissolved by reaction with cyanide in alkaline solution, the further change of frequency is linearly related to cyanide concentration in the range 10^-3–10^-4 M at pH 10.4. Only silver(I) and mercury(II) interfere if EDTA is added.     

Effect of the diffuse double layer on the interpretation of EQCM results in dilute NaClO4 solutions

The response of the electrochemical quartz crystal microbalance (EQCM) in dilute NaClO₄ solutions was studied with gold and iron electrodes during a stepwise increase of the perchlorate concentration. In the range from 10⁻⁴ M to 7.8×10⁻² M, the quartz resonant frequency of the 10 MHz AT cut crystals increased by about 700 Hz, indicating a mass loss on the electrode. A model was developed in which the diffuse double layer and the oscillating bulk electrolyte layer, characterised by the velocity decay length of the damped shear wave in solution, are treated as two independent, superimposed sheets. By assuming a characteristic thickness of the diffuse double layer according to the Gouy–Chapman theory and by treating the diffuse double layer as a rigid sheet, the measured mass loss could be simulated qualitatively. The viscosity changes in the diffuse double layer as well as in the sensed electrolyte bulk layer were found to be negligible in the concentration range investigated. In dilute solutions, the frequency shift following a concentration change is entirely due to thinning of the diffuse double layer with increasing concentration. The results demonstrate the importance of diffuse double layer effects for EQCM measurements in dilute electrolytes.     

Determination of micromolar concentrations of cyanide in solution with a piezoelectric detector

The silver plated electrodes of a piezoelectric quartz crystal are partly dissolved by cyanide in pH 9.6 solution during a 15-min immersion. The resulting frequency change of the crystal, measured in air, is proportional to cyanide concentration over the range 10^-7–10^-5 M.     

Mechanisms of micellization and rheology of PEO-PPO-PEO triblock copolymers with various architectures

Micelle formation was followed by micro-DSC and rheology for aqueous solutions of two copolymers of PEO-PPO-PEO, the Pluronic F127 (from BASF) and the EG56 (from PolymerExpert), a branched copolymer built with three chains of F127 type. It is shown that micellization is endothermic and that, for both polymers, the enthalpy of formation/melting is proportional to total concentration. The rheology of the solutions was carefully analyzed, before gelation for F127, and it reveals firstly the progressive changes of solubility of the unimers (decease of relative solution viscosity), followed by micelle formation over a 10 degrees C range. In this range, the micelle concentration dependence on temperature was deduced from enthalpy measurements and the corresponding volume fractions were derived. Viscosity was interpreted within the framework of well-known theories for hard sphere suspensions (Krieger-Dougherty or Quemada) based on an analogy between micelles and nanosized hairy grain suspensions. The gel state is achieved due to formation of the colloidal crystal. For EG56, the rheology is quite different; as the aggregation increases with temperature, a progression is observed from Newtonian to visco-elastic liquid. The characteristic frequency, defined by the relation G(') = G('), for EG56 varies with temperature and the corresponding times increase by two orders of magnitude according to an Arrhenius law. The frequency dependence of G(') and G(') at different temperatures can be superposed with a horizontal shift factor and a small amplitude adjustment. There is no elastic solid formation in this case. The "gelation" of these two copolymers is compared to the physical gelation of cold-set gels (gelatin).     

Oscillating frequency of piezoelectric quartz crystal in solutions

Oscillating frequencies of a piezoelectric crystal were measured in various solutions. One side of the crystal surface was coated with a silicon sealant. This coating was useful for measuring the oscillation of crystals in solutions for a wide range of products of density (?) and viscosity (η) and in electrolyte solutions. For measurement in solutions, the frequency change depended on the circuit used, whereas for measurements in air the circuit did not influence the frequency change. All experimental data showed that the frequency change from pure water, ΔF_w, followed ΔF_w = ? K(√?η ? √?_wη_w) except for electrolyte and polymer solutions, where K is a proportionality constant, η_w the density of pure water and η_w the viscosity of water.     

Salt-induced thickening and gelation of a poly(carboxylate) having three kinds of hydroxyl groups

A salt-induced physical gelation was found for the aqueous solution of poly(carboxylate)s having three kinds of hydroxyl groups, i.e., primary, tertiary and one on a hemiacetal ring. The gelation point (critical salt concentration) was positively correlated with the content of the hemiacetal component, while the previously confirmed hydrogen bond between the hemiacetal OH and –COO⁻ group does not seem to essentially contribute to the physical gelation. Above a critical polymer concentration, the solution viscosity was first decreased and then increased with increasing NaCl concentration, leading to gelation. However, below the critical polymer concentration, the viscosity decreased. These different behaviors of the solution viscosity depending on the polymer concentration were ascribed to a preferential promotion of intermolecular or intramolecular hydrogen bonds among the hemiacetal OH groups above and below the critical polymer concentration, respectively.     

Monitoring of morphology and physical properties of cultured cells using a micro camera and a quartz crystal with transparent indium tin oxide electrodes after injections of glutaraldehyde and trypsin

For investigating the effects of chemical stimulation to cultured cells, we have developed a quartz crystal sensor system with a micro charge-coupled device (CCD) camera that enables microphotograph imaging simultaneously with quartz crystal measurement. Human hepatoma cell line (HepG2) cells were cultured on the quartz crystal through a collagen film. The electrode of the quartz crystal was made of indium tin oxide (ITO) transparent electrodes that enable to obtain a transparent mode photograph. Glutaraldehyde and trypsin were injected to the chamber of the cells, respectively. The response of the quartz crystal was monitored and microphotographs were recorded, and the resonance frequency and resonance resistance were analyzed with an F-R diagram that plotted the resonance frequency and resonance resistance. In the case of the glutaraldehyde injection, the cells responded in two steps that included the fast response of the cross-linking reaction and the successive internal change in the cells. In the case of the trypsin injection, the responses included two processes. In the first step, cell adhesion factors were cleaved and the cell structure became round, and in the next step, the cells were deposited on the quartz crystal surface and the surface of the cells was directly in contact with the quartz crystal surface.     

Measurement of the viscosity of ferroelectric liquid crystals in free-standing films

A new implementation of the technique for the measurement of the Goldstone mode rotational viscosity in the S_c phase is presented. An electric field is applied parallel to the surface of a free-standing liquid crystal film. The optical transmission change of the film is recorded. The viscosity can be calculated from the reorientation time between optically separated positions of the director. A comparison with the viscosity values measured in thin cells is given. The values determined in cells are always higher than the results obtained from free-standing films. This indicates the great influence of the forces of interaction between the liquid crystal molecules and the surface layer in the cells.     

Bipolar pulse conductometric monitoring of ion-selective electrodes: Part 2. Studies with the fluoride-selective electrode

Bipolar pulse conductometric monitoring of the fluoride ion-selective electrode (i.s.e.) is evaluated. It is shown that fluoride ion, in addition to affecting the electrode potential, also can have two effects upon the total resistance of the electrode. Fluoride ion can enter a gel layer on the surface of the doped lanthanum fluoride crystal; solution concentrations as low as 10^-9 M fluoride can significantly decrease the gel resistance. Fluoride concentrations in the potentiometric working range of the i.s.e. can also increase the electrode resistance. The conductometric detection limit is 2–4 decades lower than the potentiometric detection limit. However, because of the resistance factors, the conductometric curve is not monotonic, and shows a maximum at a fluoride concentration in the vicinity of the potentiometric detection limit. The two resistive changes possible have different time dependences; the decrease of the gel layer resistance becomes predominant at long measurement times, while the increase of the crystal resistance predominates within the first minute of exposure to solution. Hydroxide is shown to affect the i.s.e. potential and lower the gel layer resistance. Response time to changes in fluoride concentration are less than 15 s and do not show the strong concentration dependence observed potentiometrically. The i.s.e. is shown to have a slightly lower resistance to fluoride entering the crystal than to fluoride leaving it. The small resistive dependence on direction of ion migration may indicate a directional dependence of activation energy for ion transport across the membrane solution interfaces.     

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.