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PubMed1994

Ultrasonically assisted electrospray ionization for LC/MS determination of nucleosides from a transfer RNA digest.

The use of an ultrasonic nebulizer to assist electrospray ionization mass spectrometry (ESI-MS) has been described and demonstrated with the analysis of a transfer RNA digest by microcolumn LC. The restricted range of mobile-phase compositions amenable to the electrospray process has traditionally placed a severe limitation on the types of LC applications that can be used with ESI-MS. For this reason, an ultrasonic nebulizer configured for LC has been developed that can generate the fine dispersion of liquid required for ESI-MS from any type of mobile phase. In the case presented here, a transfer RNA was enzymatically digested into its substituent nucleosides, which were then analyzed by microcolumn LC. The required mobile-phase gradient (beginning at 5% methanol) falls outside the solvent range that can be used with conventional electrospray. The ultrasonic nebulizer, however, resolves this problem. The fundamental behavior of the four most common nucleosides (cytidine, adenosine, guanosine, uridine) was studied, and conclusions concerning the effects of solution chemistry were drawn. Specifically, signal from the H+ adducts of these species seems to be strongly dependent on the pKa value. Also, effects from several source operating variables were examined. These included capillary exit voltage, drying and focusing gases, and nebulizer frequency. Performance was found to be consistent over a wide range (0-100% methanol) of mobile-phase compositions. The limit of detection for adenosine injected onto a microcolumn was found to be 100 amol. Finally, nucleosides from as little as 150 fmol of RNA (amount prior to digestion) could be detected.

Chromatography, Liquid↗

PubMed1994

LC/ESI-MS determination of proteins using conventional liquid chromatography and ultrasonically assisted electrospray.

Conventional unassisted electrospray ionization mass spectrometry (ESI-MS) has severe limitations as a liquid chromatography (LC) interface due to the few solvent compositions which can be electrosprayed without some type of assistance. LC mobile phases which have high flow rates (over 5 microL/min), high conductivity, or high surface tension are normally unsuitable for use with ESI. For this reason, an ultrasonic nebulizer has been developed which mechanically creates the fine spray of droplets needed for ESI and thus functions independently of the solvent composition. This device also operates at considerably higher liquid flow rates, up to several hundred microliters per minute. To characterize the system's performance, the ultrasonic nebulizer frequency, source electrode potentials, and drying and focusing gas flow rates were studied and optimized. Also, droplet size measurements were taken using a phase-Doppler anemometer, which showed consistent nebulizer performance up to a liquid flow rate of several hundred microliters per minute. Finally, the ultrasonic nebulizer was used for an LC application involving the separation of proteins on 1.0 and 2.1 mm i.d. columns. LC flow rates of up to 200 microL/min of mobile phases containing 0.1% trifluoroacetic acid could be easily nebulized. With the 1.0 mm i.d. column, as little as 32 fmol of cytochrome c could be detected in selected ion monitoring mode.

Chromatography, Liquid↗

PubMed2001

Generating multiply charged protein ions by ultrasonic nebulization/multiple channel-electrospray ionization mass spectrometry.

An ultrasonic nebulization/multiple channel electrospray ionization (USN/MC-ES) source, which generates multiply charged peptides and proteins ions, was developed. The source is an ultrasonic nebulizer that is connected to a multiple channel electrospray ionization source. Aerosols were formed by ultrasonically nebulizing the sample solution. The aerosols were then purged into the central channel of a seven-channel ES source via nitrogen gas. A methanol solution that contained 1% trifluroacetic acid was electrosprayed through the outlying six electrosprayers. Detection of multiply charged peptide and protein ions indicated that electrospray was generated from the charged droplet containing analyte. The sample aerosol appeared to fuse with the charged methanol droplet in the air. Then electrospray ionization of the analyte occurred from the newly formed droplet. The peptide and protein prepared in deionized water were detected by this USN/MC-ES-MS. By varying the electrospray solvents, the signals of certain components in the mixture were selectively suppressed.

Aerosols↗

PubMed2006

Combined rheological and ultrasonic study of alginate and pectin gels near the sol-gel transition.

The sol-gel transition of biopolymer mixtures has been investigated by rheological and ultrasonic measurements. A scaling analysis of the data was performed for both types of measurements. A gel time was determined from rheology for the pure pectin samples, and the data could be fitted to a universal scaling form near the transition point. Its critical exponents are in good agreement with the predictions of scalar percolation theory. In addition, the ultrasonic signal of the pectin samples close to the transition was analyzed in terms of a high-frequency scaling approach for the attenuation and the velocity. For the alginate samples and the mixtures, for which the gel point cannot be determined reliably from rheology, the ultrasonic measurements were analyzed using the same scaling form as for the pectin sample, thus providing a method for estimating the gel point, even in the absence of rheological data.

Alginates↗

PubMed2005

Ultrasonically induced degradation and detoxification of microcystin-LR (cyanobacterial toxin).

Cyanobacterial toxins (CBTs), produced by glue-green algae, are one of the most common naturally occurring toxins found in potable waters. The microcystin family of CBTs present in drinking water sources poses a considerable threat to human health. In this study, we have demonstrated that ultrasonic irradiation at 640 kHz leads to rapid degradation of microcystin-LR (MC-LR). Degradation of MC-LR present in the crude cyanobacterial extracts containing cell constituents has been studied with ultrasound under a variety of conditions. The degradation of MC-LR was demonstrated over a concentration range from 0.03 to 3.0 microM. Hydroxyl radical scavenger experiments indicate that hydroxyl radical is responsible for a significant fraction of the observed degradation, but other processes (hydrolysis/ pyrolysis) are also important. Analysis of the protein phosphatase inhibition activity of the reaction products indicates that the products from ultrasonic degradation of MC-LR do not exhibit any measurable biological activity. The results demonstrate that ultrasonic irradiation maybe an effective and practical method for the detoxification of microcystins from drinking water.

Cyanobacteria↗

PubMed1996

Development of inherently echogenic liposomes as an ultrasonic contrast agent.

Ultrasonic contrast agents have been developed for improved assessment of blood flow and tissue perfusion. Many of these agents are not inherently acoustically reflective (echogenic), and nearly all are not suitable for tissue specific targeting. The purpose of this study was to develop acoustically reflective liposomes, which are suitable for antibody conjugation, without using gas or any other agent entrapment. Echogenic liposomes were prepared from phosphatidylcholine (PC), phophatidylethanolamine (PE), phosphatidylglycerol (PG), and cholesterol (CH), using a dehydration/rehydration method. The formulation was optimized for higher acoustic reflectivity by varying the lipid composition. Liposomes were imaged with a 20 MHz intravascular ultrasonic imaging catheter. Echogenicity levels were expressed using pixel gray scale. The presence of PE and PG at specific concentrations improved echogenicity due to their effects on liposomal morphology as confirmed by freeze-etch electron microscopy. The acoustic reflectivity of liposomes was retained when liposomes were treated with blood at room temperature and 37 degrees C under in vitro conditions. It was demonstrated that the liposomes were also acoustically reflective in vivo after they were injected into a miniswine model. We have developed echogenic liposomes that are stable and suitable for tissue specific targeting as a novel contrast agent. This new contrast agent can be used for ultrasonic image enhancement and/or treatment of targeted pathologic sites.

Cholesterol↗

PubMed2001

Polydisulfides of substituted phenols as effective protectors of peroxidase against inactivation by ultrasonic cavitation.

Kinetics of inactivation of horseradish peroxidase (HP) induced by low-frequency ultrasonic (US) treatment (27 kHz) with the specific power of 60 W/cm2 were studied in phosphate (pH 7.4) and acetate (pH 5.2) buffers within the temperature range of 36.0 to 50.0 degrees C and characterized by effective first-order rate constants of US inactivation k(in)(us) in min(-1). Values of k(in)(us) depend on the specific ultrasonic power within the range of 20-60 W/cm2, on the concentration of HP, and on pH and temperature of the solutions. The activation energy of US inactivation of HP is 9.4 kcal/mole. Scavengers of HO* radicals, mannitol and dimethylformamide, significantly inhibit the US inactivation of HP at 36.0 degrees C, whereas micromolar concentrations of polydisulfide of gallic acid (poly(DSG)) and of poly(2-aminodisulfide-4-nitrophenol) (poly(ADSNP)) virtually completely suppress the US inactivation of peroxidase at the ultrasonic power of 60 W/cm2 on the sonication of the enzyme solutions for more than 1 h at pH 5.2. Various complexes of poly(DSG) with human serum albumin effectively protect HP against the US inactivation in phosphate buffer (pH 7.4). The findings unambiguously confirm a free radical mechanism of the US inactivation of HP in aqueous solutions. Polydisulfides of substituted phenols are very effective protectors of peroxidase against inactivation caused by US cavitation.

Disulfides↗

PubMed2000

Observation of yeast cell movement and aggregation in a small-scale MHz-ultrasonic standing wave field.

Aggregation of suspended yeast cells in a small-scale ultrasonic standing wave field has been monitored and quantified. The aggregation effect is based on the acoustic radiation force, which concentrates the cells in clumps. The ultrasonic chamber employed (1.9 MHz, one wavelength pathlength) had a sonication volume of 60 microl. The aggregation process was observed from above the transducer through a transparent glass reflector. A distinct, reproducible, pattern of clumps formed rapidly in the sound field. The sound pressure was estimated experimentally to be of the order of 1 MPa. Microscopic observations of the formation of a single clump were recorded onto a PC. The time dependent movement patterns and travelling velocities of the cells during the aggregation process were extracted by particle image velocimetry analysis. A time dependent change was seen in the particle motion pattern during approach to its completion of clump formation after 45 s. Streaming eddies were set-up during the first couple of seconds. The scale of the eddies was consistent with Rayleigh micro-streaming theory. An increase in the travelling velocity of the cells was observed after 30 s from initially about 400 microm s(-1) to about 1 mm s(-1). The influence of a number of mechanisms on particle behaviour (e.g. micro-streaming, particle interactions and convective flow) is considered. The experimental set-up introduced here is a powerful tool for aggregation studies in ultrasonic standing waves and lays the foundation for future quantitative experiments on the individual contributions of the different mechanisms.

Acoustics↗

PubMed2000

Breakdown of immobilisation/separation and morphology changes of yeast suspended in water-rich ethanol mixtures exposed to ultrasonic plane standing waves.

Some physiological/morphological changes have been reported before, when suspended yeasts have been irradiated with well-defined ultrasonic standing, as well as propagating, plane waves around 2.2 MHz, as used in ultrasonic coagulation, e.g., for cell filtering. Thus we used yeast as a biological model to explore the reasons for both those morphology changes and some unusual macroscopic behaviour in the case of water-rich ethanol mixtures when used as carrier liquid. When the cells were suspended in 12% (v/v) ethanol-water mixture separation was greatly reduced; the yeast cells were not retained in the pressure nodal planes of the standing wave, but mixed turbulently through the separation system. How this behaviour alters the efficiency of retention/immobilisation was measured. As the viability of the yeast was decreased as well the morphology of the cells was examined using transmission electron microscopy. Two effects, according to the type of assessment, were evident; a disruption of the cells vacuole and also damage to the cell wall/membrane complex. The extent of the alterations in vacuole structure with sonication time, utilising a fluorescent vacuole membrane dye, was measured. Transient cavitation was not detected and thus could be excluded as being responsible for the observed effects. Other possible reasons for the disruption of the intracellular compartments may be acoustic pressure, displacement or other, secondary effects like (sub) harmonic cavitation. The investigations contribute to a better understanding of the physical conditions experienced when a cell is stressed in a high-frequency ultrasonic wave in the MHz range.

Ethanol↗

PubMed2000

Investigation of enhancement of two processes, sedimentation and conjugation, when bacteria are concentrated in ultrasonic standing waves.

Cells aggregate and can be recovered from suspension when exposed to an ultrasonic standing wave field. The acoustic force on individual cells in a standing wave decreases with particle volume. A plane ultrasonic field generated by a transducer driven at 3.3 MHz was used here to investigate the removal of Escherischia coli, cells with dimensions of the order of 1.0 microm, from batch suspension by sedimentation over a range of concentrations (10(3) to 10(10) cells ml(-1)). Cell removal efficiencies greater than 90% were achieved at initial concentrations of 10(10) cells ml(-1). Removal efficiencies decreased gradually to zero, as initial bacterial concentration was reduced to 10(7) cells ml(-1). It was found that, when low concentrations of E. coli (10(3) to 10(5) cells ml(-1)) were added to suspensions of larger particles (i.e. yeast cells) that were of sufficient concentration to form aggregates in the sound field, E. coli could be harvested to an efficiency of 40%. The results imply that the E. coli became trapped and sediment with aggregates of larger particles. Some strains of bacteria are capable of DNA transfer by conjugation. The transfer rate of E. coli RP4 plasmid is order of magnitudes greater when conjugation occurs on solid medium rather than in liquid suspension. We have investigated whether the conjugation rate would also be higher in ultrasonically induced E. coli clumps than in free suspension. The donor strain was mixed with a recipient strain of E. coli, then sonicated in a capillary at 4.6 MHz in a tubular transducer for 5 min. The bacteria aggregated successfully. Results showed a three-fold increase in the rate of conjugation compared to a liquid mating control.

Bacteriological Techniques↗

PubMed1995

Some factors associated with the ultrasonic nebulization of proteins.

Ultrasonic nebulization of lactate dehydrogenase (LDH) was investigated using a DeVilbiss "Aerosonic" nebulizer. The enzyme (8ml, 0.025 mg/ml Na2HPO4, pH 7.0) was completely inactivated after 20 minutes of operation. However, the inactivation profile observed during ultrasonic nebulization was different from that previously observed using air-jet nebulization. At least two mechanisms are involved, one associated with heating and the other with aerosol production. By preventing heating of the nebulizer fluid during operation, the denaturation profile was dramatically altered. By additionally including 0.01% w/v Tween 80 or 1% w/v PEG 8000, almost all activity was retained. Similar results were obtained by preventing aerosol production and heating. However, 100% of activity was lost when heating was allowed to occur without aerosol formation. The results demonstrate that cooling in conjunction with a surfactant is one approach that could be used to stabilize proteins to ultrasonic nebulization. However, cooling also significantly reduced solute output from the nebulizer. When operated at 10 degrees C output was negligible. At 50 degrees C the output was 5x greater than that found at room temperature. The median droplet size (micron(s)) was not significantly influenced by the operating temperature of the nebulizer fluid (3.6 +/- 0.4, 21 degrees C; 3.9 +/- 0.2, 50 degrees C, p = NS (n = 6)) although the size distribution was noted to increase at the higher temperature.

Aerosols↗

PubMed2004

Perspectives on the role of ultrasonic devices in thrombolysis.

Reperfusion strategies in acute myocardial infarction and thrombotic vascular occlusion are focused on rapid and complete restoration of antegrade flow in the infarct-related artery in order to maximize myocardial salvage. Due to the limitations of fibrinolytic agents in restoration of vascular flow, ultrasonic clot dissolution alone and concomitantly with fibrinolytic, anti-thrombotic and echocardiographic contrast agents has been intensively studied during the last 2 decades. Ultrasound thrombolysis has been tested in-vitro and in-vivo as well as in patients with acute thrombotic occlusions. We review currently available techniques and methods of ultrasonic thrombolysis and present recent clinical and experimental data. The future role of ultrasonic thrombolysis and the strategy of "power thrombectomy" for treatment of acute coronary syndromes is also discussed.

Catheterization↗

PubMed2000

In vitro assessment of an ultrasonic flowmeter for use in ventilated infants.

An ultrasonic flowmeter could be advantageous over a differential pressure pneumotachograph having a constant error in varying conditions. The in vitro accuracy of ultrasonic tidal volume (VT) estimates for ventilated infants were evaluated. Flow linearity and frequency response were tested, as was the influence of humidity and oxygen content on the accuracy of VT estimates. The linearity was within the 5% limits between -350 and 350 mL x sec(-1) and was not affected by the presence of an endotracheal tube (ET). The frequency response was flat and unaffected by an ET up to 4.5 Hz. The VT in the range 7-100 mL, in air showed a mean error of 0.1% (95% confidence interval (CI) -0.2-0.4%) with a maximum and minimum of 6.5 and -3.5% respectively. Humidity did not affect accuracy. After calibration in air, the maximal mean error for measurements in pure oxygen was 3.0% (95% CI 1.9-4.1%). Repeated measurements over 5.5 h had a mean error of 0.4% (95% CI -0.7-0.1%). The in vitro evaluation of an ultrasonic flowmeter showed stable accuracy in mechanical ventilation conditions. Changing connection geometry and oxygen content did not increase the error to a clinically relevant degree. The flowmeter could therefore be a better alternative than the pneumotachograph for ventilated infants.

Humans↗

PubMed2003

Displacement amplitude of ultrasonic scaler inserts.

OBJECTIVES: Scanning laser vibrometry is a noninvasive method of measuring the velocity, displacement amplitude and oscillation frequency of vibrating objects. The purpose of this study was to assess, using a scanning laser vibrometer (SLV), the performance of different designs of commercially available ultrasonic scaler generators by measuring the oscillatory characteristics of various scaler tips. METHODS: Four ultrasonic generators were tested (Cavitron SPS and Cavitron Select (Dentsply, York, PA, USA) and Piezon Master 400 and Mini Piezon (Electro-Medical Systems, Switzerland)) with various designs of scaler tip. The tips were positioned with their anterior surface perpendicular to the direction of the laser. A graduated scale, placed over the manufacturer's power dial, enabled incremental power setting selection. For each power setting, the laser beam from the SLV was scanned over the surface of the oscillating tip. RESULTS: The ranges of longitudinal displacement amplitudes (in micrometres) were as follows: Mini Piezon (P-tip): 12.90+/-1.44 to 44.03+/-7.80; Piezon Master 400 (P-tip): 16.02+/-2.66 to 35.85+/-5.29; Cavitron SPS (TFI-10 tip): 7.81+/-0.51 to 29.70+/-1.12; Cavitron Select (TFI-10 tip): 13.13+/-1.44 to 33.77+/-4.27; Cavitron SPS (TFI-3 tip): 5.50+/-0.46 to 31.35+/-3.62. CONCLUSIONS: This study shows that there are differences between commercially available generators and that tip movement varies between tips of the same style as well as between the generator and tip design. Users of ultrasonic scalers should be made aware of this inherent variability that may influence clinical procedures.

Dental High-Speed Technique↗

PubMed2003

Ultrasonic dental scaler: associated hazards.

BACKGROUND: The ultrasonic dental scaler is a valuable tool in the prevention of periodontal disease; however, this equipment has a number of hazards with which it is associated. These include heating of the tooth during scaling, vibrational hazards causing cell disruption, possible platelet damage by cavitation, associated electromagnetic fields that can interrupt pacemakers, auditory damage to patient and clinician and the release of aerosols containing dangerous bacteria. OBJECTIVE: To collate the research reported on the various hazards associated with the ultrasonic dental scaler and discuss possible future research areas. DATA SOURCES: The scientific literature was searched using Web of Science, EMBASE and Medline, and the results of these were then hand-searched to eliminate nonrelevant papers. CONCLUSIONS: This review outlines some of the research conducted into these areas of associated hazard in order to assess their significance in the clinical situation, and discusses ideas for future research. Suggestions of recommendations are given, which have been previously investigated for their aid in reducing possible hazards, to ensure the safe working of ultrasonic scalers in the dental practice.

Air Microbiology↗

PubMed2000

An in vitro investigation into the cutting action of ultrasonic radicular access preparation instruments.

The aim of this study was to investigate the dentine cutting action of a CT4 and SJ4 radicular preparation inserts (Excellence in Endodontics/Analytic Technology, Orange, CA, USA) used in a Piezon Master 400 ultrasonic handpiece (Electro Medical Systems SA, Nyon, Switzerland). Calibration of the ultrasonic inserts was carried out at minimum, medium and maximum power settings using light microscopic measurement of the tip displacement amplitudes (x120 mag). Polished dentine samples were instrumented, at monitored loads, at the three chosen power settings, to produce uniform dentine cuts. The resultant dentine debris was collected for SEM analysis, and comparison with that produced by rotary instruments. The depth of dentine cut was measured at x30 magnification. Fracture of the SJ4 insert was noted at medium power setting. Results revealed a significant increase in both displacement amplitude and depth of dentine cut with power setting (ANOVA P < 0.001). Dentine chip size increased with power, and differed in structure and appearance from those produced by rotary instruments. In conclusion, ultrasonic cutting is influenced significantly by power setting, and dentine chip formation is fundamentally different to rotary instrumentation.

Analysis of Variance↗

PubMed1992

Effect of a social companion on the ultrasonic vocalizations and contact responses of 3-day-old rat pups.

Rat pups that are isolated in a novel environment emit ultrasonic calls. Vocalization in 3-day-old pups has been thought to be predominantly under thermal control (Allin & Banks, 1971). By the 2nd week of life, ultrasonic vocalizations are reduced when pups are tested in the company of a single anesthetized littermate (Carden & Hofer, 1990a; Hofer & Shair, 1978). In the present study, it was demonstrated that the vocalization rate of 3-day-old pups is also decreased when an anesthetized littermate is present in the isolation chamber. To determine whether this quieting was a function of the body heat of the companion, in a 2nd experiment, the axillary temperature of the companion was lowered until it was the same as the ambient temperature of the test chamber, 22 degrees C. In the presence of a cool companion, ultrasonic vocalizations were also reduced. For the last experiment, a textured plastic surrogate was substituted for the littermate. Calls were not diminished in the presence of the surrogate.

Animals↗

PubMed1983

Gonadal hormone activation of male courtship ultrasonic vocalizations and male copulatory behavior in castrated male deer mice (Peromyscus maniculatus bairdi).

The influence of testosterone (T), a 5 alpha-reduced metabolite of T, dihydrotestosterone, and an aromatized metabolite of T, estradiol, on 35-kHz ultrasonic calling and male copulatory behavior by male deer mice (Peromyscus maniculatus bairdi) was examined. Daily treatment with testosterone propionate (TP), dihydrotestosterone propionate (DHTP), or estradiol benzoate (EB) restored male ultrasonic calling in long-term castrated males. Both TP and DHTP restored male copulatory behavior, but EB was ineffective in facilitating copulation. Synergism of EB and DHTP action was observed; when subthreshold doses of EB (1 microgram/day) and DHTP (50 micrograms/day) were administered in combination, male ultrasonic calling and male copulatory behavior were activated. In relation to other comparative findings, these results indicate that the degree to which male sexual behavior is facilitated by 5 alpha-reduced androgens and/or estrogens is influenced by the species and the particular pattern of masculine behavior under consideration.

Animals↗