A cold water, ultrasonically activated stream efficiently removes proteins and prion-associated amyloid from surgical stainless steel.

BACKGROUND: Sterile service department decontamination procedures for surgical instruments struggle to demonstrate efficient removal of the hardiest infectious contaminants, such as prion proteins. A recently designed novel system, which uses a low pressure ultrasonically activated, cold water stream, has previously demonstrated efficient hard surface cleaning of several biological contaminants. AIM: To test the efficacy of an ultrasonically activated stream for the removal of tissue proteins, including prion-associated amyloid, from surgical stainless steel surfaces. METHODS: Test surfaces were contaminated with 22L, ME7 or 263K prion-infected brain homogenates. The surfaces were treated with the ultrasonically activated water stream for contact times of 5 and 10 s. Residual proteinaceous and amyloid contamination were quantified using sensitive microscopic analysis, and immunoblotting was used to characterize the eluted prion residues before and after treatment with the ultrasonically activated stream. FINDINGS: Efficient removal of the different prion strains from the surgical stainless steel surfaces was observed, and reduced levels of protease-susceptible and -resistant prion protein was detected in recovered supernatant. CONCLUSION: This study demonstrated that an ultrasonically activated stream has the potential to be a cost-effective solution to improve current decontamination practices and has the potential to reduce hospital-acquired infections.

Cavitation clusters in lipid systems - Ring-up, bubble population, and bifurcated streamer lifetime.

The processing of oils is vital to their ultimate use within the food industry. Control over the physical properties of such materials could be achieved through the application of high-intensity ultrasound (HIU). However, the exact mechanism, centred upon acoustic cavitation, is currently unclear. To investigate the cavitation environment in oils further, the ring-up of a HIU source in an oil media is studied in the presence and absence of a pre-existing bubble population. High-speed imaging and acoustic measurements within the system is demonstrated to be extremely useful in characterising the dynamics present under non steady-state conditions. The behaviour of the clusters generated in the first 1000 ms under these conditions is shown to be significantly different depending on the bubble population. A bifurcated streamer (BiS), originating from a unique bi-cluster event, is only observable in the presence of a bubble population during the ring-up process to higher cluster orders. In addition, the lifetime of this BiS event is highly temperature dependent and is shown to be a good marker for the viscosity of the oil employed.

Cavitation clusters in lipid systems - surface effects, local heating and streamer formation.

Cavitation clusters and streamers are characterised in lipid materials (specifically sunflower oil) and compared to water systems. The lipid systems, which are important in food processing, are studied with high-speed camera imaging, laser scattering and pressure measurements. In these oils, clusters formed at an aged (roughened) tip of the sound source (a piston like emitter, PLE) are shown to collapse with varied periodicity in relation to the drive amplitude employed. A distinct streamer (an area of increased flow emanating from the cavitation cluster) is seen in the lipid media which is collimated directly away from the tip of the PLE source whereas in water the cavitation plume is visually less distinct. The velocity of bubbles in the lipid streamer near the cluster on the order of 10 m s-1. Local heating effects, within the streamer, are detected using a dual thermocouple measurement at extended distances. Viscosity, temperature and the outgassing within the oils are suggested to play a key role in the streamer formation in these systems.

Microsecond resolution of cavitation bubble dynamics using a high-speed electrochemical impedance approach.

A new method to detect the uncompensated resistance, the capacitance and the Faradaic current at an electrode exposed to ultrasonic cavitation is presented. The method enables these parameters to be resolved with a 2 microsecond resolution and relies on the detection of the impedance of an electrode recorded as a function of time with a suitable AC excitation signal (here 500 kHz). Data obtained from an aluminium electrode, held under potentiostatic control, is used to illustrate the technique with particular relevance to the effects of cavitation bubbles generated by ultrasound. Analysis of the data recorded shows that the cavitation bubbles form close to the surface of the electrode and collapse, causing damage to the passive film formed at the aluminium surface. The capacitance, uncompensated resistance and Faradaic signals are used to explore the dynamic processes and show expansion and collapse of bubbles prior to erosion/corrosion. The close proximity of the bubbles to the surface is deduced from the reductions in capacitance and increases in resistance prior to bubble collapse, which is then shown to trigger the onset of a Faradaic signal, thus confirming the erosion/corrosion mechanism previously assumed.

Electrochemical 'bubble swarm' enhancement of ultrasonic surface cleaning.

An investigation of surface cleaning using a swarm of gas bubbles within an acoustically activated stream is presented. Electrolysis of water at Pt microwires (100 µm diameter) to produce both hydrogen and oxygen bubbles is shown to enhance the extent of ultrasonic surface cleaning in a free flowing water stream containing an electrolyte (0.1 M Na2SO4) and low surfactant concentration (2 mM SDS). The surfactant was employed to allow control of the average size of the bubble population within the swarm. The electrochemical bubble swarm (EBS) is shown to perturb acoustic transmission through the stream. To optimise the cleaning process both the ultrasonic field and the electrochemical current are pulsed and synchronized but with different duty cycles. Cleaning action is demonstrated on structured surfaces (porcine skin and finger mimics) loaded with fluorescent particles. This action is shown to be significantly enhanced compared to that found with an inherent bubble population produced by the flow and acoustic regime alone under the same conditions.

Cold water cleaning of brain proteins, biofilm and bone - harnessing an ultrasonically activated stream.

In the absence of sufficient cleaning of medical instruments, contamination and infection can result in serious consequences for the health sector and remains a significant unmet challenge. In this paper we describe a novel cleaning system reliant on cavitation action created in a free flowing fluid stream where ultrasonic transmission to a surface, through the stream, is achieved using careful design and control of the device architecture, sound field and the materials employed. Cleaning was achieved with purified water at room temperature, moderate fluid flow rates and without the need for chemical additives or the high power consumption associated with conventional strategies. This study illustrates the potential in harnessing an ultrasonically activated stream to remove biological contamination including brain tissue from surgical stainless steel substrates, S. epidermidis biofilms from glass, and fat/soft tissue matter from bone structures with considerable basic and clinical applications.

Removal of Dental Biofilms with an Ultrasonically Activated Water Stream.

Acidogenic bacteria within dental plaque biofilms are the causative agents of caries. Consequently, maintenance of a healthy oral environment with efficient biofilm removal strategies is important to limit caries, as well as halt progression to gingivitis and periodontitis. Recently, a novel cleaning device has been described using an ultrasonically activated stream (UAS) to generate a cavitation cloud of bubbles in a freely flowing water stream that has demonstrated the capacity to be effective at biofilm removal. In this study, UAS was evaluated for its ability to remove biofilms of the cariogenic pathogen Streptococcus mutans UA159, as well as Actinomyces naeslundii ATCC 12104 and Streptococcus oralis ATCC 9811, grown on machine-etched glass slides to generate a reproducible complex surface and artificial teeth from a typodont training model. Biofilm removal was assessed both visually and microscopically using high-speed videography, confocal scanning laser microscopy (CSLM), and scanning electron microscopy (SEM). Analysis by CSLM demonstrated a statistically significant 99.9% removal of S. mutans biofilms exposed to the UAS for 10 s, relative to both untreated control biofilms and biofilms exposed to the water stream alone without ultrasonic activation (P < 0.05). The water stream alone showed no statistically significant difference in removal compared with the untreated control (P = 0.24). High-speed videography demonstrated a rapid rate (151 mm(2) in 1 s) of biofilm removal. The UAS was also highly effective at S. mutans, A. naeslundii, and S. oralis biofilm removal from machine-etched glass and S. mutans from typodont surfaces with complex topography. Consequently, UAS technology represents a potentially effective method for biofilm removal and improved oral hygiene.

Confined plasmons in metallic nanocavities.

We investigate the properties of gold surfaces patterned using a nanoscale "lost wax" technique by electrochemical deposition through a self-assembled latex template. Near-spherical gold nanocavities within the resulting porous films support localized surface plasmons which couple strongly to incident light, appearing as sharp spectral features in reflectivity measurements. The energy of the resonances is easily tunable from ultraviolet to near infrared by controlling the diameter and height of the nanocavities. The energies of these features agree well with the Mie resonances of a perfect spherical void.

Electrochemical evidence of H' produced by ultrasound.

Electrochemical evidence of H. produced by cavitation as the result of ultrasonic irradiation of an aqueous solution is presented.

An Enzyme Switch Employing Direct Electrochemical Communication between Horseradish Peroxidase and a Poly(aniline) Film.

An enzyme switch, or microelectrochemical enzyme transistor, responsive to hydrogen peroxide was made by connecting two carbon band electrodes (∼10 µm wide, 4.5 mm long separated by a 20-µm gap) with an anodically grown film of poly(aniline). Horseradish peroxidase (EC 1.11.1.7) was either adsorbed onto the poly(aniline) film or immobilized in an insulating poly(1,2-diaminobenzene) polymer grown electrochemically on top of the poly(aniline) film to complete the device. In the completed device, the conductivity of the poly(aniline) film changes from conducting (between - 0.05 and + 0.3 V vs SCE at pH 5) to insulating (>+0.3 V vs SCE at pH 5) on addition of hydrogen peroxide. The change in conductivity is brought about by oxidation of the poly(aniline) film by direct electrochemical communication between the enzyme and the conducting polymer. This was confirmed by measuring the potential of the poly(aniline) film during switching of the conductivity in the presence of hydrogen peroxide. The devices can be reused by rereducing the poly(aniline) electrochemically to a potential below +0.3 V vs SCE. A blind test showed that the device can be used to determine unknown concentrations of H(2)O(2) in solution and that, when used with hydrogen peroxide concentrations below 0.5 mmol dm(-)(3), the same device maybe reused several times. The possible development of devices of this type for use in applications requiring the measurement of low levels of hydrogen peroxide or horseradish peroxidase is discussed.

A study on the effect of ultrasound on electrochemical phenomena.

We have employed microelectrodes in order to resolve single transient cavitation events. High time resolution studies of individual current time transients were shown. Distance and temperature dependencies proved to be in agreement with both the acoustic pressure field generated by the ultrasonic horn and cavitation bubble collapse violence with decreasing vapour pressure within the bubble, respectively. Measurements of electrode kinetics at the point of impact of the transient events were shown for the first time by the employment of sampled voltammetry.

Determination of heterogeneous electron transfer kinetics in the presence of ultrasound at microelectrodes employing sampled voltammetry.

The technique of sampled voltammetry at microelectrodes irradiated with ultrasound is demonstrated for the first time. This technique is used to determine the heterogeneous electron transfer rate constants for the redox couples ferrocene/ferrocenium, Ru(NH(3))(6)(3+/2+), and IrCl(6)(3)(-)/IrCl(6)(2)(-). Determination of the heterogeneous rate constants is also achieved for comparison purposes by analysis of fast sweep rate voltammetry of the redox systems studied at microelectrodes and comparison of the results obtained to the theory developed by Nicholson and Shain. The heterogeneous rate constants determined using sampled voltammetry were 1.0, 0.6, 1.23, and 0.18 cm s(-)(1) for the ferrocene/ferrocenium (0.1 mol dm(-)(3) TEATFB, CH(3)CN), Ru(NH(3))(6)(3+/2+) (0.1 mol dm(-)(3) KCl), IrCl(6)(3)(-) (1 mol dm(-)(3) KCl), and IrCl(6)(3)(-)/IrCl(6)(2)(-) (1 mol dm(-)(3) NaCl), respectively, in agreement with those obtained in the absence of ultrasound.