Ultrasonic Standing Wave Research Articles

On Chemical and Ultrasonic Strategies to Improve a Portable FT-IR ATR Process Analyzer for Online Fermentation Monitoring

A setup for online fermentation monitoring was tested with suspensions containing yeast cells. A flow cell was equipped with a horizontal attenuated total reflection (ATR) unit for measurements of mid-infrared spectra. The stopped flow principle was employed to separately assess the liquid and the dispersed cells: dissolved components in the supernatant can be assessed while pumping the fermentation broth through the flow cell. Upon stopping the flow the culture can be monitored as the microorganisms settle onto the horizontal ATR diamond. Due to the surface sensitivity of ATR spectroscopy cleanness of the optical element is of particular importance. For yeast fermentations the formation of biofilms on the ATR surface was identified as limitation in regard to long-term stability. Initial experiments showed that the effective removal of residues was impossible by rinsing with water or a NaHCO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> solution. Therefore, various cleaning agents (2%) have been tested for their ability to clear off the biofilm. The problem of biofilm formation was additionally addressed by the exploitation of forces exerted on suspended particles within an ultrasonic standing wave (USW). The USW ( ~2 MHz) was built up between the ATR element and an ultrasonic transducer facing it. This technique of ultrasonic particle manipulation was applied to actively lift the sedimented material from the ATR after the infrared measurement, thus have the rinsing stream carry it away more effectively. Among the studied reagents surfactants and oxidizing agents showed to be most effective, the use of an USW was found to be feasible to remove a biofilm.

Quartz crystal microbalance biochip with ultrasonic standing wave enhancement

This study designs, fabricates and tests a novel biochip containing a quartz crystal microbalance (QCM) sensor and a piezoelectric transducer which enhances performance by production of ultrasonic standing waves (USW). Biotin–streptavidin binding is used as a model in real experiments with a prototype USW–QCM biochip to verify that USW enhancement greatly improves biochip detection sensitivity and reduces detection time by increasing the effective analyte concentration. Fabrication methodology is detailed and underlying theory is given. The presented design shows good promise for development into a practical commercial system for enhanced real-time in situ detection of protein–ligand interactions in medical and pharmaceutical applications.

Ultrasonic manipulation in microfluidic chips for accurate bioparticle handling.

Micro-manipulation of cells or other bioparticles has important applications in biological and biomedical research. Dielectrophoresis and optical tweezers are the classical tools in this field. Ultrasonic standing wave (USW) technology is presently emerging as powerful alternative, especially in microfluidic chips and other miniaturized systems. In this contribution we will review our present activities in USW-based particle manipulation in microfluidic chips. Recent experiments and simulations allow us to tailor the spatial distribution of the USW force field by multi-frequency actuation and appropriate microchannel/transducer resonance design. We introduce the concept of ultrasonic micro-cages for single-cell or single-particle 3-D ultrasonic manipulation. It is shown that these manipulation tools can be combined with high-resolution optical microscopy, thereby allowing state-of-the-art characterization of individual cells. Frequency-modulation is shown to stabilize the manipulation performance as well as allowing flow-free transport of particles and cells. Environmental control inside the channels has been achieved and proliferation and viability studies are promising. Finally, for bio-analysis, we demonstrate potential for femtomolar bio-analytical sensitivity in bead-based assays using USW enrichment.

The Effect of Frequency Sweeping and Fluid Flow on Particle Trajectories in Ultrasonic Standing Waves

Particle concentration and separation in ultrasonic standing waves through the action of the acoustic radiation force on suspended particles are discussed. The acoustic radiation force is a function of the density and compressibility of the fluid and the suspended particles. A two-dimensional theoretical model is developed for particle trajectory calculations. An electroacoustic model is used to predict the acoustic field in a resonator, driven by a piezoelectric transducer. Second, the results of the linear acoustic model are used to calculate the acoustic radiation force acting on a particle suspended in the resonator. Third, a particle trajectory model is developed that integrates the equation of motion of a particle subjected to a buoyancy force, a fluid drag force, and the acoustic radiation force. Computational fluid dynamics calculations are performed to calculate the velocity field that is subsequently used to calculate fluid drag. For a fixed frequency excitation, the particles are concentrated along the stable node locations of the acoustic radiation force. Through a periodic sweeping of the excitation frequency particle translation is achieved. Two types of frequency sweeps are considered, a ramp approach and a step-change method. Numerical results of particle trajectory calculations are presented for two configurations of flow-through resonators and for two types of frequency sweeping. It is shown that most effective particle separation occurs when the fluid drag force is orthogonal to the acoustic radiation force.

Proliferation and viability of adherent cells manipulated by standing-wave ultrasound in a microfluidic chip

Ultrasonic-standing-wave (USW) technology has potential to become a standard method for gentle and contactless cell handling in microfluidic chips. We investigate the viability of adherent cells exposed to USWs by studying the proliferation rate of recultured cells following ultrasonic trapping and aggregation of low cell numbers in a microfluidic chip. The cells form 2-D aggregates inside the chip and the aggregates are held against a continuous flow of cell culture medium perpendicular to the propagation direction of the standing wave. No deviations in the doubling time from expected values (24 to 48 h) were observed for COS-7 cells held in the trap at acoustic pressure amplitudes up to 0.85 MPa and for times ranging between 30 and 75 min. Thus, the results demonstrate the potential of ultrasonic standing waves as a tool for gentle manipulation of low cell numbers in microfluidic systems. (E-mail: jessica.hultstrom@biox.kth.se)

Separation and Concentration of Particles in Fluid Using Ultrasonic Standing Wave

This paper presents the theory, design, and evaluation of a smart device for the enhanced separation of particles mixed in fluid. The smart device takes advantage of the ultrasonic standing wave, which was generated by the operation of a piezoceramic PZT patch installed in the smart device. The details of the device design including the electro-acoustical modelling for separation and PZT transducer are described at first. Based on this design, the separation device was fabricated and evaluated. In the experiments, an optical camera with a zoom lens was used to monitor the position of particles within the separation channel layer in the device. The electric impedance of the PZT patch bonded on the separation device was measured .The device shows a strong levitation and separation force against 50μm diameter particles mixed with water at the separation channel in the device. Experimental results also showed that the device can work at both heavy and light sand particles mixed with water due to the generated standing wave field in the separation channel.

Fluorescein isothiocynate-dextran uptake by chinese hamster ovary cells in a 1.5 mhz ultrasonic standing wave in the presence of contrast agent

Uptake of fluorescein isothiocynate-dextran (FITC-dextran) by Chinese hamster ovary cells was studied after exposure to ultrasonic standing wave (USW) in presence of Optison®, an ultrasound contrast agent. Confluent Chinese hamster ovary cells were harvested and suspended in phosphate-buffered saline + 0.1% bovine serum albumin containing FITC-dextran (10, 40, and 500 kDa) at 10 μM final concentration. The suspension was seeded with contrast agent (75 μL/mL) and exposed to a 1.5 MHz USW system at acoustic pressures ranging from 0.98 to 4.2 MPa. Macromolecular uptake was assessed by fluorescent microscopy and quantified by flow cytometry 10 min after exposure. FITC-dextran positive cells, as assessed by flow cytometry, were 1 ± 0.05% and 2.58 ± 0.27% for acoustic pressures of 1.96 and 4.2 MPa, respectively ( p = 0.006). Fluorescent microscopy indicated a degree of macromolecular loading at 0.98 MPa with 46% of peripherally FITC-dextran- and/or propidium iodide-stained cells coincident with the appearance of significant frequency ( f 0/2 and 2 f 0) emission signals. At higher pressures, high macromolecular loading with 6% peripherally stained cells at 1.96 MPa was associated with lower order emission signals and white noise. The study conclusively demonstrates macromolecular loading in an USW, a significantly higher macromolecular loading at higher pressures and indicates potential of emission signals for a feedback loop to control the acoustic power outputs and fine-tune the biologic effects associated with sonoporation. (E-mail: AmsoNN@cf.ac.uk)

Ultrasonic standing wave manipulation technology integrated into a dielectrophoretic chip

Several cell-based biological applications in microfluidic systems require simultaneous high-throughput and individual handling of cells or other bioparticles. Available chip-based tools for contactless manipulation are designed for either high-precision handling of individual particles, or high-throughput handling of ensembles of particles. In order to simultaneously perform both, we have combined two manipulation technologies based on ultrasonic standing waves (USWs) and dielectrophoresis (DEP) in a microfluidic chip. The principle is based on the competition between long-range ultrasonic forces, short-range dielectrophoretic forces and viscous drag forces from the fluid flow. The ultrasound is coupled into the microchannel resonator by an external transducer with a refractive element placed on top of the chip, thereby allowing transmission light microscopy to continuously monitor the biological process. The DEP manipulation is generated by an electric field between co-planar microelectrodes placed on the bottom surface of the fluid channel. We demonstrate flexible and gentle elementary manipulation functions by the use of USWs and linear or curved DEP deflector elements that can be used in high-throughput biotechnology applications of individual cells.

Numerical Simulation of a Single Bubble Rising in an Ultrasonic Standing Wave Field

The behavior of a single bubble rising in an ultrasonic standing wave field through vertical pipes filled with a quiescent liquid is analyzed numerically using the cubic-interpolated pseudo-particle(CIP)-combined and unified procedure(C-CUP) method. The calculated terminal velocities of bubbles in pipes agree with the experimental results in silicon oil. As the diameter of the bubble approaches the pipe diameter, the shape of the bubble is deformed into a lengthwise ellipse and rising velocity slows due to the pipe wall. The velocities and shapes of single bubbles are obtained for both standing waves formed in the axial direction of pipes and in the radial direction. When an initial spherical bubble rises through the node of the radially formed standing wave in pipes, it is deformed into a lengthwise elliptical shape by the acoustic radiation force even if the wall effect is small, and the velocity of the bubble is faster than that for when there is no ultrasonic field. In other cases, the average terminal velocity of bubbles is slower than that for when there is no ultrasonic field.

Numerical Analysis of a Single Solid Spherical Particle Falling in an Ultrasonic Standing Wave Field

The velocities of particle falling in a standing wave field through a vertical pipes filled with a stagnant liquid in are analyzed numerically for Reynolds number (Re)<1, for a wide range of pipe diameters. The equations of motion of a spherical particle in a viscous fluid are solved based on the Basset-Boussinesq-Ossen (BBO) equation to clarify the falling velocities in an infinite stagnant fluid, and two-dimensional hydrodynamic equations based on the cubic-interpolated pseudo-particle (CIP)-combined and unified procedure (C-CUP) method to clarify the effects of the walls of pipes. The velocity of a particle is periodically changed due to the influence of the radiation force of the standing wave. The average terminal velocity in a standing wave field is lower than that for which there is no ultrasonic field. As the particle diameter approaches the pipe diameter, the velocity of the particle approaches zero due to the influence of the pipe wall. The C-CUP method effectively simulates the behavior of a particle falling through a liquid-filled pipe in the standing wave field.

On the Technology of Acoustic Utility. Acoustic Information and Energy. Behavior of a Single Solid Spherical Particle Rising or Falling in an Ultrasonic Standing Wave Field.

The purpose of this report is to clarify the behavior of single solid particles falling or rising in liquids with a standing wave field. The behavior of particles in degassed and ion exchanged water in the formation of a standing wave field was studied experimentally using an ultrasonic field of 45 kHz. In the experiment for particles falling in liquids, the decreased velocity of the glass particles in the ultrasonic field exhibited the greater deceleration In the degassed water, since the ultrasonic power effectively acts on a particle as a radiation force. In the case of the rising experiment, however, the greater deceleration of a particle is obtained in the ion exchanged water due to the motion of cavitaion bubbles. On the basis of this study, the falling velocity of a particle was analyzed numerically. The equation for motion of a sphere in a viscous fluid is based on the Basset-Boussinseq-Ossen equation, in addition to which, the acoustic radiation force must be included. The velocity of a particle is periodically changed due to influence of the radiation force of the standing wave. The terminal velocity of a small particle in an ultrasonic field is lower than that for which there is no ultrasonic field.

On the Technology of Acoustic Utility. Acoustic Information and Energy. Two-Dimensional Micromanipulation Using an Ultrasonic Standing Wave Field Generated by Crossing Sound Beams.

As a non-contact maicromanipulation technique, it is possible to trap particles in water at nodes of an ultrasonic standing wave field generated between a transducer and a reflector and to transport them using a frequency-shifting operation. Since there are several problems coming from resonance of the sound field with this scheme, the authors proposed a novel manipulation technique for particles using a standing wave field generated by two transducers whose sound beam axes were crossing to each other and accomplished one-dimensional manipulation of a polystyrene particle. The present paper describes an extension of this method adding one more transducer, which realizes two-dimensional manipulation suppressing unstable motion observed in the one-dimensional operation. Experiments in water using polystyrene particles confirmed the principle of the two-dimensional manipulation and agreed well with a numerical analysis of the sound field.

Orientation of Fibers in Liquid by Ultrasonic Standing Waves

The orientation of fibers in a liquid irradiated with ultrasound is studied to realize the noncontact directional control of reinforcing fibers in the molten matrix of a composite material. The equations of translational and rotational motions of a fiber in a standing wave field are derived. The numerical solutions show the movement of the fibers at various initial positions and their stable positions and directions. Experiments are performed using polystyrene fibers of various lengths suspended in an aqueous sugar solution. Both numerical and experimental results indicate that polystyrene fibers shorter than one-fourth of the wavelength are constrained at the pressure node and are oriented in the direction perpendicular to that of wave propagation. On the other hand, fibers ranging from one-fourth to one-half of the wavelength have orientation either parallel to the direction of wave propagation at the pressure loop or perpendicular to that at the pressure node depending on their initial positions and directions.

Atomization of Liquids with Widely Differing Material Properties by Ultrasonic Standing-Waves

Ultrasonic standing wave fields in a gaseous atmosphere, generated by two opposed, identical transducers (20 kHz) are used as standing wave atomization (USWA) to produce very fine narrow sized spherical droplets. USWA may be operated under ambient gas pressure or under gas pressures of up to 2.0 MPa (and more) thus allowing disintegration of fluids with high viscosities (synthetic resins, glass melts, suspensions) and/or high surface tensions (metal melts). The feed is led from above into the central sound pressure node of the standing wave field. Here the cylindrical liquid jet is deformed into a flat circular disk parallel to the transducer surfaces. At the rim of this disk atomization into ultrafine droplets takes place, the size distribution of which can be fitted by a log-normal distribution with (in the case of tin particles) a mean diameter of 10 μm and a geometrical standard deviation between 1.6 and 1.9. In order to gain quantitative insight into the dependence of the droplet size on the atomization conditions, a dimensional analysis was carried out, leading to two equations for the mean drop size of either metal melts or highly viscous liquids and showing significant influences of either the Weber-number or the Reynolds-number together with the ratio of the kinetic energy density of the gas flow (in the USWA field) and the feed. A description of the apparatus and of the process conditions gives an impression about the necessary hardware of this new technique which has its main claim in the disintegration of liquids with very high viscosities and/or high surface tensions and in the contamination free atomization into ultrafine spherical particles.

Particle Manipulation by Ultrasonic Standing Wave Fields to complement dynamic light scattering experiments

AbstractDynamic light scattering is a widely used technique for the sizing of colloidal suspensions. It is capable of measuring particles across the size range from approximately 1 nm to several microns. However the larger particle sizes tend to pose problems for the interpretation of the scattered light signal either by virtue of their light scattering efficiency relative to the smaller species present or the departure of the scattered light signal from Gaussian statistics. Rapid removal of such particles in‐situ could extend the use of dynamic light scattering particularly in on‐line analysis or laboratory automated measurement. In this paper a method is demonstrated for the in‐situ removal of larger particles in suspension by means of ultrasonic standing waves and concurrent dynamic light scattering measurement. The theory behind ultrasonic particle manipulation and its effect on the motion of the particles is discussed. Data from a scattering cell designed to incorporate the ultrasonic technology is presented showing that dynamic light scattering measurements may be carried out under such conditions. Varying the energy density of the ultrasonic field allows particles greater than a defined cut‐off diameter to be removed from the measurement region. Theory shows that the minimum cut‐off size may be as small as 100 nm. Results presented here demonstrate complete removal at a lower diameter threshold of approximately 2000 nm.

Observation of Ultrasonic Standing Waves using the Dye/Paper Method: Possible Implications for Bioeffects of Sonication

Experiments are described which show how an aqueous solution of methylene blue, a cationic dye, may be used to record characteristic striations when a sheet of Astralux card, normally used for printin

Conditions of Coherence in Diffraction Spectra Produced in Liquids on Ultrasonic Standing Waves

Conditions of Coherence in Diffraction Spectra Produced in Liquids on Ultrasonic Standing Waves

Segregation and sedimentation of red blood cells in ultrasonic standing waves.

THE formation of bands of red cells in the blood vessels of live chick embryos during ultrasonication has been reported by Dyson, Woodward and Pond1. It was suggested that the segregation was primarily caused by Bernoulli forces between the cells owing to the displacement of the cells relative to the plasma, and that the standing wave was operative only in fixing the position of the segregation pattern. Here we suggest that it is primarily the standing wave which is the cause of the segregation.

Diffraction of a Gaussian Light Beam by Cylindrical Ultrasonic Standing Waves

This paper presents some results of theoretical and experimental examination of the farfield diffraction of a Gaussian light beam that has passed axially through a cylindrical ultrasonic standing wave. The range of parameters within which the light-beam diameter and sound wavelength are comparable is particularly emphasized. The theoretical approach is appropriate to the range of parameters for which the ultrasonic perturbation of refractive index may be characterized as an axially symmetric phase grating. Although the diffraction integral was not completely integrated in terms of familiar functions, some potentially useful expressions for the average and the time-dependent light intensities were obtained. Theoretical and experimental results are in good agreement.

Fourier Series for Intensity of Light Modulated by Ultrasonic Standing Waves

Fourier Series for Intensity of Light Modulated by Ultrasonic Standing Waves