An acoustic dielectric and mechanical spectrometer

In this report, the dielectric constant of glycerol solutions (0-70% (w/w)) and the mechanical transitions of poly(2-hydroxylethyl methacrylate-co-methacrylic acid) films (600-800 nm, 1.5-10 mol% cross-linker) have been investigated by the magnetic acoustic resonance sensor (MARS), which is an electrode-free acoustic sensor and operates over a continuous frequency spectrum (6-200 MHz). When a glycerol solution was loaded, the response of the MARS decayed exponentially as the operating frequency was increased. The decay rate against frequency as a function of the glycerol concentration reflects the change of the dielectric property of the glycerol solutions. In addition, mechanical relaxation of the poly(2-hydroxylethyl methacrylate-co-methacrylic acid) film has been observed on the MARS and the corresponding viscoelastic transition frequency has been estimated. The viscoelastic transition frequency increased as the polymer was more highly cross-linked. The MARS system behaved as a dielectric and mechanical spectrometer, monitoring the electrical and mechanical properties of viscoelastic materials or on the solid-liquid interfaces simultaneously, which has prospective application in studies of biomaterials, molecular interactions and drug deliveries.     

Implementation of acoustic, radiofrequency and microwave rotating fields in analytical plasma sources

Four helium plasma sources operating at atmospheric pressure have been developed for analytical emission spectrometry by applying a synchronically rotating field with three or more phases operating at 1 kHz, 27 MHz or 2.45 GHz. The plasma takes the form of a disk and has minimum field strength at the axis. Thus, a channel is formed at the center through which the sample in the form of wet aerosol or a chemically generated vapor of halogen may be introduced. A dual-flow concentric ceramic injector was used to supply helium plasma gas and the sample to the plasma. The helium plasma operated at low power levels (40-300 W) and low gas flow rates of below 3 L min^− 1 and was self-igniting. The acoustic, radio-frequency (rf) and microwave-driven plasmas can withstand wet aerosol loadings of 5, 30 and 100 mg min^− 1, respectively, generated by an ultrasonic nebulizer without a desolvation unit. The plasma physical characteristics were compared at these three frequencies under otherwise similar operating conditions. The helium excitation temperature, OH rotational temperature and electron number density increased with increasing frequency in ranges of 2800-4000 K, 1100-3200 K and 0.1-7 × 10¹⁴ cm^− 3, respectively. To demonstrate the effect of frequency on the plasma excitation efficiency the emission intensity from halogen ions was evaluated using chemical vapor generation with continuous sampling without desiccation. Using 3-phase microwave, 6-phase microwave, 4-phase rf and 1 kHz helium plasma sources the detection limits (3σ) for chlorine at 479.40 nm were 26, 60, 230 and 1200 ng mL^− 1, respectively. The microwave-driven plasma was the densest and had the highest excitation potential toward chlorine and bromine ions.     

Blood platelet adhesion to protein studied by on-line acoustic wave sensor

The attachment of blood platelets to the surface of bare and protein-coated thickness-shear mode acoustic wave devices operating in a flow-through configuration has been studied. Platelets in washed from bind to the gold electrodes of such sensors, but the resulting frequency shifts are far less than predicted by the conventional mass-based model of device operation. Adherence to albumin and various types of collagen can be produced by on-line introduction of protein or by a pre-coating strategy. Differences in attachment of platelets to collagen types I and IV and the Horm variety can be detected. Platelets attached to collagen yield an interesting delayed, but reversible signal on exposure to a flowing medium of low pH. Scanning electron microscopy of sensor surfaces at various time points in this experiment reveals that originally intact platelets are eventually destroyed by the high acidity of the medium. The reversible frequency is attributed to the presence of removable platelet granular components at the sensor-liquid interface.     

Longitudinal acoustic mode in polymers. V. Nature of perturbing forces in n-paraffins and polymers

Binary mixtures of n-paraffins have been examined by Raman spectroscopy in order to elucidate the nature of the perturbations on the chains. For a short-chain species diluted in a longer-chain species, the longitudinal acoustic mode frequency of the former decreases from its value in the pure state to that corresponding to a chain with free ends. This observation, as well as others, confirms our previous suggestions that longitudinal perturbing forces are responsible for increasing this frequency over its unperturbed value. These results also provide new insights into the structures present in solid solutions of n-paraffins. They reemphasize the necessity of incorporating the effects of such perturbations in applications of the longitudinal acoustic mode to morphological studies of polymers.     

Picosecond acoustic transmission measurements. II. Probing high frequency structural relaxation in supercooled glycerol

The high frequency acoustic response of liquids is measured in a manner directly analogous to conventional ultrasonic measurements. Two thin metal films act as acoustic transducer and receiver for a liquid layer between them. Pulsed optical excitation generates high bandwidth wave packets in the transducer, and these are detected in the receiver after damping and dispersion by the liquid. This initial measurement probes structural relaxation dynamics of glycerol in the frequency range 2-20 GHz, for temperatures between 235 and 291 K. The analysis presented here demonstrates the presence of excess relaxation, not accounted for by either the alpha or beta relaxation of the mode-coupling theory, and suggests the presence of constant loss in the susceptibility spectrum of supercooled glycerol.     

Acoustic determination of polymer molecular weights and rotation times

An acoustic waveguide device was shown to be sensitive to the molecular weight of poly(ethylene glycol) in solution over a molecular weight range determined by the operating frequency of the device. The acoustic device used generates a shear wave with displacement in the plane of the device surface and normal to the direction of propagation. Liquid over the device exhibits viscous coupling to the oscillating surface, affecting propagation of the acoustic wave. The propagation loss was shown to be directly proportional to the weight percentage of the solute. For a given weight percent of polymer in solution, the loss increased with increasing molecular weight until a maximum loss value was reached; this may be due to the fact that rotational times for polymer molecules increase with molecular weight until they reach a point at which the rotation is limited by the oscillation time on the device surface. The molecular weight at which the maximum loss value was attained was 10,000 g/mol for a device operating at 104 MHz and 3350 g/mol for a device operating at 331 MHz, implying a rotational time of 1 ns for each 2200 increase in molecular weight. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1490–1495, 2002     

Errors induced in quartz crystal mass uptake measurements by nongravimetric effects: Considerations beyond the EerNisse caution

We report frequency changes in AT‐cut quartz crystals for glassy polymers subsequent to temperature and carbon dioxide pressure changes. Anomalous frequency shifts are observed for the crystal subsequent to such changes. Since, the Sauerbrey equation has been applied routinely for mass uptake measurements in glassy polymers, using the quartz crystal microbalance fitted with AT‐cut quartz crystals, it is important that nongravimetric effects that impact the frequency change be well understood. In the present work, we provide a quantitative analysis of the breakdown of the Sauerbrey equation for viscoelastic materials by using the Johannsmann (Macromol Chem Phys 1999, 200, 501) treatment of the response of AT‐cut crystals. Clearly, there exist significant errors in mass uptake measurements for materials deposited on AT‐cut quartz crystals when precautions pertaining to film thickness and viscoelastic compliance are ignored. We show that while the early caution of EerNisse on stress effects in AT‐cut quartz crystals can be important in mass uptake measurements, for polymers, the major source of error arises from viscoelastic effects in the coating. We conclude that mass uptake measurements for films of compliant materials and polymers above their glass transition cannot be performed with accuracy, using AT‐cut quartz crystals if the results are not corrected for frequency shifts due to viscoelastic effects of the overlayer unless the films are extremely thin, that is, less than 100 nm. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 801–814, 2006     

Alcohol determination using an acoustic wave sensor

An acoustic wave methodology was developed to quantify alcohols in aqueous solutions. The frequency at minimum impedance of a bare quartz crystal in contact with ethanol solutions was found to be a suitable parameter to quantify ethanol. Ethanol in several Portuguese white wines was analyzed both by the proposed methodology and by the usual areometric method with no statistically significant differences (alpha = 0.05) in precision or accuracy of the results.     

Theory and application of a quartz resonator as a sensor for viscous liquids

A comprehensive analysis of the interaction between an AT-cut quartz crystal resonator and a viscous fluid is presented. The analysis, which includes peizoelectric effects, assumes a liquid of finite extent and therefore could also be used to study thin film of viscous liquids. A novel continuous flow cell system was designed and fabricated to monitor viscosity using an 11-MHz quartz crystal resonator. Measured data for frequency shifts of aqueous solutions of alcohols and sugars are in excellent agreement with theory.     

Interfacial behavior of immortalized hypothalamic mouse neurons detected by acoustic wave propagation

The attachment of immortalized hypothalamic murine neurons onto the surface of an acoustic wave device yields both positive series resonant frequency (f(s)) and motional resistance (R(m)) shifts as opposed to commonly reported negative f(s) and positive R(m) shifts observed for other cell types. These unique shifts have been confirmed by a variety of experiments in order to verify the source and the validity of the signals. These studies involved monitoring responses to solution flow, the absence of serum proteins, the effect of reducing specific cell -surface interactions and the disruption of the neuronal cytoskeleton components. For the adhesion and deposition of neurons, f(s) and R(m) shifts are positively correlated to the amount of adhered neurons on the sensor surface, whereas non-adhered neurons do not produce any significant change in the monitored parameters. In the absence of serum proteins, initial cell adhesion is followed by subsequent cell death and removal from the sensor surface. The presence of the peptide, GRGDS is observed to significantly reduce cell-surface specific interactions compared to the control of SDGRG and this produces f(s) and R(m) responses that are opposite in direction to that observable for cell adhesion. Cytoskeletal studies, using the drugs nocodazole (10 μM), colchicine (1 μM), cytochalasin B (10 μM) and cytochalasin D (2 μM) all elicit neuronal responses that are validated by phalloidin actin-filament staining. These results indicate that the responses are associated with a wide range of cellular changes that can be monitored and studied using the acoustic wave method in real time, under optimal physiological conditions.     

Supercooling of aqueous NaCl and KCl solutions under acoustic levitation

The supercooling capability of aqueous NaCl and KCl solutions is investigated at containerless state by using acoustic levitation method. The supercooling of water is obviously enhanced by the alkali metal ions and increases linearly with the augmentation of concentrations. Furthermore, the supercooling depends on the nature of ions and is 2-3 K larger for NaCl solution than that for KCl solution in the present concentration range: Molecular dynamics simulations are performed to reveal the intrinsic correlation between supercoolability and microstructure. The translational and orientational order parameters are applied to quantitatively demonstrate the effect of ionic concentration on the hydrogen-bond network and ice melting point. The disrupted hydrogen-bond structure determines essentially the concentration dependence of supercooling. On the other hand, the introduced acoustic pressure suppresses the increase of supercooling by promoting the growth and coalescence of microbubbles, the effective nucleation catalysts, in water. However, the dissolved ions can weaken this effect, and moreover the degree varies with the ion type. This results in the different supercoolability for NaCl and KCl solutions under the acoustic levitation conditions.     

Label-free detection of neuron-drug interactions using acoustic and Kelvin vibrational fields

Kelvin and acoustic fields of high-frequency have been employed in the non-invasive investigation of immortalized hypothalamic neurons, in order to assess their response to different concentrations of specific drugs, toxins, a stress-reducing hormone and neurotrophic factors. In an analytical systems biology approach, this work constitutes a first study of living neuron cultures by scanning Kelvin nanoprobe (SKN) and thickness shear mode (TSM) acoustic wave techniques. N-38 hypothalamic mouse neurons were immobilized on the gold electrode of 9 MHz TSM acoustic wave devices and gold-coated slides for study by SKN. The neurons were exposed to the neurochemicals betaseron, forskolin, TCAP, and cerebrolysin. Signals were collected with the TSM in real-time mode, and with the SKN in scanning and real-time modes, as the drugs were applied at biologically significant concentrations. With the TSM, for all drugs, some frequency and resistance shifts were in the same direction, contrary to normal functioning for this type of instrument. Possible mechanisms are presented to explain this behaviour. An oscillatory signal with periodicity of approximately 2 min was observed for some neuron-coated surfaces, where the amplitude of these oscillations was altered upon application of certain neurotrophic factors. These two new techniques present novel and non-invasive electrodeless methods for detecting changes at the cellular level caused by a variety of neuroactive compounds, without killing or destroying the neurons.     

A new study of the enzymatic hydrolysis of carboxymethyl cellulose with a bulk acoustic wave sensor

A new bulk acoustic wave (BAW) cellulase sensing technique, which is based on the enzymatic hydrolysis process of sodium carboxymethylcellulose (CMC) by cellulase, was established. The frequency shift curves of BAW sensor indicated that the viscosity of the tested solutions decreased during the hydrolysis process. The hydrolysis rate of CMC by cellulase was calculated from the frequency shift curves. The hydrolysis rate of CMC under different pH conditions at 30°C showed that cellulase had high hydrolysis ability approximately at pH 5.0. Kinetic parameters (the Michaelis constant K_m and the maximum rate V_max) of the process were estimated by using a linear method of Lineweaver–Burk plot. K_m is 1.95±0.25 mg ml⁻¹ and V_max is −(4.25±0.58)×10⁻³ g^1/2 cm^−3/2 cP^1/2 min⁻¹. Also the activation energy (E_a) of the enzymatic hydrolysis, with a value of 51.99±1.26 kJ mol⁻¹, was estimated in this work.     

Bioelectrochemical effectiveness of low intensity acoustic exposure on ligand binding

A quantum–mechanical model is proposed to evaluate the bioelectrochemical transduction of low-intensity acoustic exposure, with reference to the binding process of a ligand (messenger) ion to a receptor protein. The interaction of the acoustic exposure with the ligand–receptor chemical reaction is assumed to be mediated by the endogenous electric field of the receptor binding crevice. The displacement of the solvent (water) molecules surrounding the protein, when exposed to the acoustic field, induces the displacement of the receptor molecules from their initial thermal equilibrium position, so that the attractive endogenous force exerted by the receptor on the ligand becomes time-varying at the frequency of the acoustic exposure. A suitable perturbing Hamiltonian operator is evaluated, which transduces the exogenous acoustic exposure into a kind of Stark effect. The density operator method is utilized to statistically evaluate the binding probability in presence of thermal noise. The typical reference intensity (power density) of the incident acoustic wave is 0.1 mW cm⁻² in the frequency range 0.5–5 MHz. Usual first-order approximation techniques are employed to evaluate in closed form the change in the binding probability, as compared as usual with its value at thermal equilibrium. By doing so, it is possible to identify a range of parameter values where resonant effects due to the acoustic exposure occur. Thus, a direct numerical integration of the equations is performed in order to validate these first-order findings. The resulting effects are very small, as compared with the binding probability under unperturbed conditions, i.e., at thermal equilibrium, which appears to be the limiting factor of the effectiveness of low-intensity acoustic exposure. These conclusions suggest future research directions, accounting for the out-of-equilibrium living state of a cell and its related basal metabolism, in order to explain those published experimental results which suggest that the binding probability may be significantly affected by a low-intensity exogenous acoustic field.     

Adsorption studies of dodecylamine at the quartz interface using an electrode-separated piezoelectric sensor

The adsorption process of dodecylammonium chloride (DAC) from aqueous solutions onto a quartz crystal interface was investigated in situ using an electrode-separated piezoelectric sensor (ESPS). Increasing amounts of DAC adsorbed onto a quartz crystal surface resulted in linearly decreasing oscillating frequencies of the ESPS. The adsorption density can be monitored by the frequency decrease. The adsorption density obtained by calculation using the Sauerbrey equation in the ESPS method is greater than that in solution depletion method. A calibration coefficient is added into the Sauerbrey equation to correct the influence of surface roughness of the quartz crystal on the adsorption density. The influence of solution properties on the adsorption density measurement was discussed. A dependence of the adsorption density on pH was reported. Received: 17 April 1997 / Revised: 1 December 1997 / Accepted: 7 December 1997     

Adsorption studies of dodecylamine at the quartz interface using an electrode-separated piezoelectric sensor

The adsorption process of dodecylammonium chloride (DAC) from aqueous solutions onto a quartz crystal interface was investigated in situ using an electrode-separated piezoelectric sensor (ESPS). Increasing amounts of DAC adsorbed onto a quartz crystal surface resulted in linearly decreasing oscillating frequencies of the ESPS. The adsorption density can be monitored by the frequency decrease. The adsorption density obtained by calculation using the Sauerbrey equation in the ESPS method is greater than that in solution depletion method. A calibration coefficient is added into the Sauerbrey equation to correct the influence of surface roughness of the quartz crystal on the adsorption density. The influence of solution properties on the adsorption density measurement was discussed. A dependence of the adsorption density on pH was reported. Received: 17 April 1997 / Revised: 1 December 1997 / Accepted: 7 December 1997     

Electrode modification and the response of the acoustic shear wave device operating in liquids

The effect of electrode polarity, geometry, and stray capacitance on the performance of the thickness-shear mode acoustic wave sensor operating in electrolytes and solutions of biomolecules has been studied. In contrast to the well-known mass-based response of the device operating in the gas phase, the response in a liquid is governed by several factors including acoustoelectric and fringing field effects, which are known to be active at the edges of the electrodes. In order to investigate and utilize these effects, we modified the electrode geometry to increase the edge length, which, in turn, raises the sensitivity of the device. These changes which constituted either complete coverage of the back of the device with electrode material, or the removal of disks and lines from the electrode surface, resulted in a two to three times enhancement of sensor response. Such modifications that extend device sensitivity beyond the electrode area to the quartz region of the sensing structure also provide a better surface for the immobilization of various probes. We verified the enhancing ability of the modified electrodes for the case of adsorption of the protein avidin and neutravidin, followed by their affinity reactions with biotinylated biomolecules. It was found that the active electrode in contact with electrolyte exhibits a sensitivity of about twice that of the grounded electrode. The existence of stray capacitance around the cell was confirmed by shielding the cell assembly with a bath of concentrated KCl solution. This shielding effect was measured to be about 25-60 Hz in series resonant frequency and -1000 Hz in parallel resonant frequency.     

葡聚糖双亲性衍生物修饰PLA亚微粒子的制备及其表面多重生物因子功能化

以胆固醇半琥珀酸酰氯对NaIO4氧化的醛化葡聚糖进行疏水改性,制备了醛基化双亲性葡聚糖衍生物Chol-Dex-CHO;利用醛基与己二酰肼酰腙化反应,实现葡聚糖主链的氨基化;生物素经二环已基碳二亚胺活化后与双亲性葡聚糖衍生物主链上的氨基偶联,形成生物素化(3%)双亲性葡聚糖(Chol-Dex-Biotin).将聚乳酸(PLA)与Chol-Dex-Biotin溶液共透析可形成亚微粒子,双亲性多糖可通过疏水基团锚定于PLA亚微粒子表面,透射电子显微镜与原子力显微镜测试观察到清晰的球形核壳结构,激光粒度仪测定亚微粒子粒径与粒径分布表明调节Chol-Dex-Biotin与PLA的配比可以控制亚微粒子的粒径(150~200 nm),X-射线光电子能谱证明亚微粒表面存在Chol-Dex-Biotin.在此基础上,以FITC标记的转铁蛋白(Tf-FITC)和生物素化兔IgG为模型生物功能因子,分别通过共价偶联及生物素-亲合素物理结合两种机理对葡聚糖包覆的PLA纳米微粒表面进行多重生物因子功能化修饰,得到表面Tf和IgG双重修饰的PLA亚微粒子(Tf-PLA-IgG submicron particles).亚微粒子表面Tf和兔IgG的结合分别通过荧光显微镜观测和抗IgG-辣根过氧化氢酶(IgG-HRP)显色反应验证.     

Rheological properties of aqueous solutions of polyethylene glycols with various molecular weights

The dependences of the kinematic viscosity of dilute aqueous solutions of polyethylene glycols (PEGs) with various molecular weights in the temperature range of 293.15–323.15 K were investigated. The intrinsic viscosity, the Huggins constant, and the activation energy of a viscous flow were calculated for these solutions. Proposals regarding the structure of polymer macromolecules in solution are made. The constants of the Mark-Kuhn-Hauvink equation required to estimate the polymer molecular weights were determined for PEG-water systems at various temperatures.     

Brillouin-scattering determination of the acoustic properties and their pressure dependence for three polymeric elastomers

The acoustic properties of three polymer elastomers, a cross-linked poly(dimethylsiloxane) (Sylgard 184), a cross-linked terpolymer poly(ethylene-vinyl acetate-vinyl alcohol), and a segmented thermoplastic poly(ester urethane) copolymer (Estane 5703), have been measured from ambient pressure to approximately 12 GPa by using Brillouin scattering in high-pressure diamond anvil cells. The Brillouin-scattering technique is a powerful tool for aiding in the determination of equations of state for a variety of materials, but to date has not been applied to polymers at pressures exceeding a few kilobars. For the three elastomers, both transverse and longitudinal acoustic modes were observed, though the transverse modes were observed only at elevated pressures (>0.7 GPa) in all cases. From the Brillouin frequency shifts, longitudinal and transverse sound speeds were calculated, as were the C(11) and C(12) elastic constants, bulk, shear, and Young's moduli, and Poisson's ratios, and their respective pressure dependencies. P-V isotherms were then constructed, and fit to several empirical/semiempirical equations of state to extract the isothermal bulk modulus and its pressure derivative for each material. Finally, the lack of shear waves observed for any polymer at ambient pressure, and the pressure dependency of their appearance is discussed with regard to instrumental and material considerations.