Single Microbubbles Research Articles

Modeling the Terminal Velocity of Rising Electrocharged Microbubbles

The generation of electrocharged microbubbles is very important for several separation processes (e.g., water treatment, paper industry, and mineral processing). However, their rising terminal velocities are not fully understood. This work presents a laboratory study of the terminal velocity of single microbubbles (bubble diameter (Db) < 100 µm) rising in stagnant aqueous solutions with different pH levels (from 2 to 12) and reagent types (frother and collector; 30 ppm). The measurements were compared with the respective predicted velocities computed from the Stokes and Hadamard–Rybczynski models. It was found that the terminal velocities of electrocharged microbubbles were larger than the respective predictions from the Stokes equation. A regression equation was proposed to predict the terminal velocity as a function of the bubble diameter, which showed considerable dispersion depending on the type of reagent adsorbed on its surface, the concentration of these reagents, and the physical characteristics that the boundary layer acquires by modifying the zeta potential of the microbubbles; this effect has not yet been addressed in the literature.

High-Speed Optical Characterization of Protein-and-Nanoparticle–Stabilized Microbubbles for Ultrasound-Triggered Drug Release

BackgroundUltrasound-triggered bubble-mediated local drug delivery has shown potential to increase therapeutic efficacy and reduce systemic side effects, by loading drugs into the microbubble shell and triggering delivery of the payload on demand using ultrasound. Understanding the behavior of the microbubbles in response to ultrasound is crucial for efficient and controlled release. MethodsIn this work, we characterize the response of microbubbles with a coating consisting of poly(2-ethyl-butyl cyanoacrylate) (PEBCA) nanoparticles and denatured casein. High-speed recordings are taken of single microbubbles, both in bright-field and fluorescence. ResultsThe nanoparticle-loaded microbubbles show resonance behavior, but with a large variation in response, demonstrating a substantial inter-bubble variation in mechanical shell properties. The probability of shell rupture and the probability of nanoparticle release were found to strongly depend on the microbubble size, and the most effective size was inversely proportional to the driving frequency. Both the rupture and release probabilities increased with increasing driving pressure amplitude. Rupture of the microbubble shell occurred after fewer cycles of ultrasound as the driving pressure amplitude or driving frequency was increased. ConclusionsThe results highlight the importance of careful selection of the driving frequency, driving pressure amplitude, and duration of the ultrasound to achieve the most efficient ultrasound-triggered shell rupture and nanoparticle release of protein-and-nanoparticle-stabilized microbubbles.

Magnetically navigated microbubbles coated with albumin/polyarginine and superparamagnetic iron oxide nanoparticles

While microbubbles (MB) are routinely used for ultrasound (US) imaging, magnetic MB are increasingly explored as they can be guided to specific sites of interest by applied magnetic field gradient. This requires the MB shell composition tuning to prolong MB stability and provide functionalization capabilities with magnetic nanoparticles. Hence, we developed air-filled MB stabilized by a protein–polymer complex of bovine serum albumin (BSA) and poly-L-arginine (pArg) of different molecular weights, showing that pArg of moderate molecular weight distribution (15–70 kDa) enabled MB with greater stability and acoustic response while preserving MB narrow diameters and the relative viability of THP-1 cells after 48 h of incubation. After MB functionalization with superparamagnetic iron oxide nanoparticles (SPION), magnetic moment values provided by single MB confirmed the sufficient SPION deposition onto BSA + pArg MB shells. During MB magnetic navigation in a blood vessel mimicking phantom with magnetic tweezers and in a Petri dish with adherent mouse renal carcinoma cell line, we demonstrated the effectiveness of magnetic MB localization in the desired area by magnetic field gradient. Magnetic MB co-localization with cells was further exploited for effective doxorubicin delivery with drug-loaded MB. Taken together, these findings open new avenues in control over albumin MB properties and magnetic navigation of SPION-loaded MB, which can envisage their applications in diagnostic and therapeutic needs.

Numerical investigation of oil droplet detachment from wall surface by a microbubble using ternary phase‐field model

AbstractIn this study, we investigated the detachment of an oil droplet from a wall surface by microbubbles (MBs) using the numerical simulation of a gas–liquid–liquid three‐phase flow based on a phase‐field model. A single MB was collided with an oil droplet adhered to a wall surface to determine whether the droplet would detach from the wall. It was confirmed that the oil droplet detached from the wall when the interfacial tension between the water and oil or between the bubble and oil was low. To clarify the mechanism, we theoretically calculated the balance of interfacial tension at the three‐fluid contact line. The lower the interfacial tension between the water and oil and between the bubble and oil, the smaller the contact angle of the oil droplet on the bubble. This increased wettability was the driving force that caused the oil droplet to detach from the wall surface.

Computational Fluid Dynamics Simulation Assessment of Inlet Configuration Influence on Enhancing Swirl Flow Microbubble Generator Performance

In this study, a CFD simulation analysis was used to predict the characteristics of a swirl flow as a reference to optimize a new design of microbubble generator. To examine the impact of the inlet design, three different configurations of the inlet type were applied, namely single inlet, double inlet, and tangent-circle inlet. The performance of the microbubble generator was characterized in terms of swirl velocity, pressure drop in radial position, and pressure distribution along the central axis of the microbubble generator. Generally, the CFD analysis succeeded to visualize the hypothetical bath of the flow streamlines inside the microbubble generators. The results illustrated that the swirl flow in the tangent-circle inlet was able to generate a negative pressure zone in the central area of the generator (i.e., self-suction mechanism). In addition, the tangent-circle inlet showed a high-pressure drop compared with the single inlet microbubble generator. Although the double inlet microbubble generator illustrated a high-pressure drop between the inlet and the outlet, the streamlines distribution was focused only on the top part of the microbubble generator. This was a reason why the self-suction mechanism was not well defined.

Sononeoperfusion effect by ultrasound and microbubble promotes nitric oxide release to alleviate hypoxia in a mouse MC38 tumor model

Tumor hypoperfusion not only impedes therapeutic drug delivery and accumulation, but also leads to a hypoxic and acidic tumor microenvironment, resulting in tumor proliferation, invasion, and therapeutic resistance. Sononeoperfusion effect refers to tumor perfusion enhancement using ultrasound and microbubbles. This study aimed to further investigate hypoxia alleviation by sononeoperfusion effect and explore the characteristics and mechanism of sononeoperfusion effect. To stimulate the sononeoperfusion effect, mice bearing MC38 colon cancers were included in this study and diagnostic ultrasound for therapy was set at a mechanical index (MI) of 0.1, 0.3, and 0.5, frequency of 3 MHz, pulse length of 5 cycles, and pulse repetition frequency of 2000 Hz. The results demonstrated that a single ultrasound and microbubble (USMB) treatment resulted in tumor perfusion enhancement at MI = 0.3, and nitric oxide (NO) concentration increased at MI = 0.3/0.5 (P < 0.05). However, there were no significant difference in the hypoxia-inducible factor-1α (HIF-1α) or D-lactate (D-LA) (P > 0.05) levels. Multiple sononeoperfusion effects were observed at MI = 0.3/0.5 (P < 0.05). For each treatment, USMB slightly but steadily improved the tumor tissue oxygen partial pressure (pO2) during and post treatment. It alleviated tumor hypoxia by decreasing HIF-1α, D-LA level and the hypoxic immunofluorescence intensity at MI = 0.3/0.5 (P < 0.05). The sononeoperfusion effect was not stimulated after eNOS inhibition. In conclusion, USMB with appropriate MI could lead to a sononeoperfusion effect via NO release, resulting in hypoxia amelioration. The tumors were not resistant to multiple sononeoperfusion effects. Repeated sononeoperfusion is a promising approach for relieving tumor hypoxia and resistance to therapy.

Experimental measurements on the microbubble characteristics and dissolved oxygen (DO) in water using single and twin-Venturi type microbubble generators

The aim of this paper is to develop low cost and low power consumption microbubble generator to improve the mass transfer of gas to liquid. Microbubble aeration used in aquaculture to improve dissolve oxygen level, water recycling through dissolved air flotation (DAF), oil refinement and reduction of skin friction on ship Hull. A single Venturi and 3 twin-Venturis microbubble generators are manufactured and tested in this study. Experimental data on microbubbles diameters distribution and dissolved oxygen are presented. The main conclusions are: i) the mean microbubbles diameters produced by twin-Venturi are smaller by 10 µm than single Venturi generator; ii) the dissolved oxygen concentration was higher for twin-Venturi microbubble generator; iii) the microbubbles size distribution from twin-Venturis have a narrower distribution which reduces the probability of bubbles coalesce as they have very close values of velocities; iv) the bubbles diameters and velocities increase with the height in the water tank.

Nonlinear ultrasound in liquid containing multiple coated microbubbles: effect of buckling and rupture of viscoelastic shell on ultrasound propagation

With promising applications in medical diagnosis and therapy, the behavior of shell-encapsula-ted ultrasound contrast agents (UCAs) has attracted considerable attention. Currently, second-generation contrast agents stabilized by a phospholipid membrane are widely used and studies have focused on the dynamics of single phospholipid shell-encapsulated microbubbles. To improve the safety and the efficiency of the methods using the propagation or targeted ultrasound, a better understanding of the propagation of ultrasound in liquids containing multiple encapsulated microbubbles is required. By incorporating the Marmottant–Gompertz model into the multiple scale analysis of two-phase model, this study derived a Korteweg–de Vries–Burgers equation as a weakly nonlinear wave equation for one-dimensional ultrasound in bubbly liquids. It was found that the wave propagation characteristics changed with the initial surface tension, highlighting two notable features of the phospholipid shell: buckling and rupture. These results may provide insights into the suitable state of microbubbles, and better control of ultrasound for medical applications, particularly those that require high precision.

Pseudo-Doppler effect at a disappearance of a single microbubble translating owing to acoustic radiation force

We attempted to visualize a single microbubble driven by acoustic radiation force using a combination of pulse inversion Doppler and plane wave imaging. Commercial microbubbles, Sonazoid® underwent ultrasound exposure with a center frequency of 5.2 MHz, a pulse repetition frequency of 4 kHz, and a negative peak sound pressure of 1.59 MPa. It succeeded in separately detecting individual microbubbles with high sensitivity. The disappearance of freely-translating microbubbles could be observed as a broadened spectrum of Doppler signal, i.e. a pseudo-Doppler effect. However, the trend was not apparent in the case of wall-colliding microbubbles.

Water treatment by cavitation: Understanding it at a single bubble - bacterial cell level

Cavitation is a potentially useful phenomenon accompanied by extreme conditions, which is one of the reasons for its increased use in a variety of applications, such as surface cleaning, enhanced chemistry, and water treatment. Yet, we are still not able to answer many fundamental questions related to efficacy and effectiveness of cavitation treatment, such as: “Can single bubbles destroy contaminants?” and “What precisely is the mechanism behind bubble's cleaning power?”. For these reasons, the present paper addresses cavitation as a tool for eradication and removal of wall-bound bacteria at a fundamental level of a single microbubble and a bacterial cell. We present a method to study bubble-bacteria interaction on a nano- to microscale resolution in both space and time. The method allows for accurate and fast positioning of a single microbubble above the individual wall-bound bacterial cell with optical tweezers and triggering of a violent microscale cavitation event, which either results in mechanical removal or destruction of the bacterial cell. Results on E. coli bacteria show that only cells in the immediate vicinity of the microbubble are affected, and that a very high likelihood of cell detachment and cell death exists for cells located directly under the center of a bubble. Further details behind near-wall microbubble dynamics are revealed by numerical simulations, which demonstrate that a water jet resulting from a near-wall bubble implosion is the primary mechanism of wall-bound cell damage. The results suggest that peak hydrodynamic forces as high as 0.8 μN and 1.2 μN are required to achieve consistent E. coli bacterial cell detachment or death with high frequency mechanical perturbations on a nano- to microsecond time scale. Understanding of the cavitation phenomenon at a fundamental level of a single bubble will enable further optimization of novel water treatment and surface cleaning technologies to provide more efficient and chemical-free processes.

Ultrasonic Traveling Waves for Near-Wall Positioning of Single Microbubbles in a Flowing Channel.

Although microbubbles are used primarily in the medical industry as ultrasonic contrast agents, they can also be manipulated by acoustic waves for targeted drug delivery, sonothrombolysis and sonoporation. Acoustic waves can also potentially remove microbubbles from tubing systems (e.g., in hemodialysis) to prevent the negative effects associated with circulating microbubbles. A deeper understanding of the interactions between the acoustic radiation force, the microbubble and the channel wall could greatly benefit these applications. In this study, single air-filled microbubbles were injected into a flowing (polydimethylsiloxane) channel and monitored by a high-speed camera while passing through a pulsed ultrasonic wave zone (0.5 MHz). This study compared various bubble sizes, flow rates and acoustic pressure amplitudes to better understand the three physical regimes observed: free bubble translation (away from the wall); on-wall translation; and bubble-wall attachment. Comparison with a theoretical model revealed that the acoustic radiation force needs to exceed the combined repulsive forces (shear lift, wall lubrication and repulsive Van der Waal forces) for the dead state of bubble-wall attachment. The bubble dynamics revealed through this investigation provide an opportunity for efficient positioning of microbubbles in a channel flow, for either in vivo manipulation or removal in biological applications.

On the theory of multiple encapsulated microbubbles interaction: Effect of lipid shell thickness

Encapsulated microbubbles are empty, micrometer-sized, spherical bubbles, typically micron which are used in many applications as lipid-shells in soft tissues. Here, this paper proposes the theoretical and mathematical modelling of the interaction of lipid-encapsulated microbubbles in soft tissues, as well as an examination of the effect of the thickness of the lipid-encapsulated microbubbles envelope located between the inner and outer radius of the microbubble. The mathematical models are formulated for a single encapsulated microbubble and interacting microbubbles in lipid shells. The first models are placed while considering the effect of shell-thickness on microbubbles in soft tissues. The second one has weak shell-thickness layers on it. In encapsulated single microbubbles and interacting microbubbles, the modified Church equations of shell-thickness microbubbles are formulated and solved analytically. Under the effect of layer thickness, the radii of outer microbubble dynamics are larger than those of inner radii of encapsulated microbubble dynamics, and the radii of bubbles with weak shell thickness in soft tissue are smaller. The clusterization of microbubbles reduces the process of microbubble growth, and interparticle interaction enhances it. In addition, the approximate value of the inner and outer microbubble radius was calculated at the different time intervals when the thickness of the shell, δ=0,15,150,250,350nm. Moreover, the growth process has been studied in different materials such as polymers, albumin, lipids, and liquids, and it turns out the results are consistent with previous works.

Numerical simulation method of nonlinear contrast-enhanced ultrasound imaging

&lt;sec&gt;Contrast-enhanced ultrasound imaging (CEUS) based on the acoustic nonlinearity of ultrasonic microbubble has received great attention in recent years. Compared with conventional linear ultrasound imaging, nonlinear CEUS can further improve the imaging resolution while overcoming the challenge of clutter filtering. Simulation, acting as an effective tool for research on new mechanisms and technologies of ultrasound imaging, has been a long-term focus of computational acoustics. In the community of biomedical ultrasound, common sound field simulation tools are mainly based on finite element method (FEM), analytical method, &lt;i&gt;k&lt;/i&gt;-space pseudospectral method and finite-difference time-domain method (FDTD), which are relatively mature solutions for simulating the nonlinear characteristics of tissue. However, it is still not trivial to simulate nonlinear CEUS by using the prevailing methods, as the nonlinearity of microbubble is often not considered.&lt;/sec&gt;&lt;sec&gt;In this paper, we propose a simulation method of nonlinear CEUS imaging that successfully combines the microbubble nonlinearity and classic &lt;i&gt;k&lt;/i&gt;-space pseudospectral method. Specifically, forced oscillation response of the microbubble is computed based on the modified Rayleigh-Plesset equation and such a nonlinear response is further dealt as an additional source for analyzing the nonlinear component propagation and CEUS imaging. To investigate the performance of the proposed method, B-mode images of single microbubble and clustered microbubbles are simulated based on plane wave imaging. The plane wave based CEUS imaging can thus be carried out with different compounding angles and different contrast pulse sequencing (CPS) strategies (pulse inversion, amplitude modulation, pulse inversion &amp; amplitude modulation, and probe element alternation). Different soft-tissue and mechanical parameters of the microbubble can be adjusted by using the proposed nonlinear simulation strategy, thus providing efficient solution for CEUS simulation. Such a method can evaluate the performances of different CPS strategies, and further contribute to the CEUS development.&lt;/sec&gt;

Blood-cerebrospinal fluid barrier opening by modified single pulse transcranial focused shockwave

Transcranial focused shockwave (FSW) is a novel noninvasive brain stimulation that can open blood-brain barriers (BBB) and blood-cerebrospinal fluid barriers (BCSFB) with a single low-energy (energy flux density 0.03 mJ/mm2) pulse and low-dose microbubbles (2 × 106/kg). Similar to focused ultrasound, FSW deliver highly precise stimulation of discrete brain regions with adjustable focal lengths that essentially covers the whole brain. By opening the BCSFB, it allows for rapid widespread drug delivery to the whole brain by cerebrospinal fluid (CSF) circulation. Although no definite adverse effect or permeant injury was noted in our previous study, microscopic hemorrhage was infrequently observed. Safety concerns remain the major obstacle to further application of FSW in brain. To enhance its applicability, a modified single pulse FSW technique was established that present 100% opening rate but much less risk of adverse effect than previous methods. By moving the targeting area 2.5 mm more superficially on the left lateral ventricle as compared with the previous methods, the microscopic hemorrhage rate was reduced to zero. We systemically examine the safety profiles of the modified FSW-BCSFB opening regarding abnormal behavior and brain injury or hemorrhage 72 hr after 0, 1, and 10 pulses of FSW-treatment. Animal behavior, physiological monitor, and brain MRI were examined and recorded. Brain section histology was examined for hemorrhage, apoptosis, inflammation, oxidative stress related immunohistochemistry and biomarkers. The single pulse FSW group demonstrated no mortality or gross/microscopic hemorrhage (N = 30), and no observable changes in all examined outcomes, while 10 pulses of FSW was found to be associated with microscopic and temporary RBC extravasation (N = 6/30), and abnormal immunohistochemistry biomarkers which showed a trend of recovery at 72 hrs. The results suggest that single pulse low-energy FSW-BCSFB opening is effective, safe and poses minimal risk of injury to brain tissue (Sprague Dawley, SD rats).

Cavitation bubble interaction with compliant structures on a microscale: A contribution to the understanding of bacterial cell lysis by cavitation treatment

Numerous studies have already shown that the process of cavitation can be successfully used for water treatment and eradication of bacteria. However, most of the relevant studies are being conducted on a macro scale, so the understanding of the processes at a fundamental level remains poor. In attempt to further elucidate the process of cavitation-assisted water treatment on a scale of a single bubble, the present paper numerically addresses interaction between a collapsing microbubble and a nearby compliant structure, that mechanically and structurally resembles a bacterial cell. A fluid–structure interaction methodology is employed, where compressible multiphase flow is considered and the bacterial cell wall is modeled as a multi-layered shell structure. Simulations are performed for two selected model structures, each resembling the main structural features of Gram-negative and Gram-positive bacterial cell envelopes. The contribution of two independent dimensionless geometric parameters is investigated, namely the bubble-cell distance δ and their size ratio ς. Three characteristic modes of bubble collapse dynamics and four modes of spatiotemporal occurrence of peak local stresses in the bacterial cell membrane are identified throughout the parameter space considered. The former range from the development of a weak and thin jet away from the cell to spherical bubble collapses. The results show that local stresses arising from bubble-induced loads can exceed poration thresholds of cell membranes and that bacterial cell damage could be explained solely by mechanical effects in absence of thermal and chemical ones. Based on this, the damage potential of a single microbubble for bacteria eradication is estimated, showing a higher resistance of the Gram-positive model organism to the nearby bubble collapse. Microstreaming is identified as the primary mechanical mechanism of bacterial cell damage, which in certain cases may be enhanced by the occurrence of shock waves during bubble collapse. The results are also discussed in the scope of bacteria eradication by cavitation treatment on a macro scale, where processes of hydrodynamic and ultrasonic cavitation are being employed.

Influence of Surface Tension on Dynamic Characteristics of Single Bubble in Free-Field Exposed to Ultrasound.

The motion of bubbles in an ultrasonic field is a fundamental physical mechanism in most applications of acoustic cavitation. In these applications, surface-active solutes, which could lower the surface tension of the liquid, are always utilized to improve efficiency by reducing the cavitation threshold. This paper examines the influence of liquids’ surface tension on single micro-bubbles motion in an ultrasonic field. A novel experimental system based on high-speed photography has been designed to investigate the temporary evolution of a single bubble in the free-field exposed to a 20.43 kHz ultrasound in liquids with different surface tensions. In addition, the R-P equations in the liquid with different surface tension are solved. It is found that the influences of the surface tension on the bubble dynamics are obvious, which reflect on the changes in the maximum size and speed of the bubble margin during bubble oscillating, as well as the weaker stability of the bubble in the liquid with low surface tension, especially for the oscillating bubble with higher speed. These effects of the surface tension on the bubble dynamics can explain the mechanism of surfactants for promoting acoustic cavitation in numerous application fields.

Super-Resolution Ultrasound Imaging Can Quantify Alterations in Microbubble Velocities in the Renal Vasculature of Rats.

Super-resolution ultrasound imaging, based on the localization and tracking of single intravascular microbubbles, makes it possible to map vessels below 100 µm. Microbubble velocities can be estimated as a surrogate for blood velocity, but their clinical potential is unclear. We investigated if a decrease in microbubble velocity in the arterial and venous beds of the renal cortex, outer medulla, and inner medulla was detectable after intravenous administration of the α1-adrenoceptor antagonist prazosin. The left kidneys of seven rats were scanned with super-resolution ultrasound for 10 min before, during, and after prazosin administration using a bk5000 ultrasound scanner and hockey-stick probe. The super-resolution images were manually segmented, separating cortex, outer medulla, and inner medulla. Microbubble tracks from arteries/arterioles were separated from vein/venule tracks using the arterial blood flow direction. The mean microbubble velocities from each scan were compared. This showed a significant prazosin-induced velocity decrease only in the cortical arteries/arterioles (from 1.59 ± 0.38 to 1.14 ± 0.31 to 1.18 ± 0.33 mm/s, p = 0.013) and outer medulla descending vasa recta (from 0.70 ± 0.05 to 0.66 ± 0.04 to 0.69 ± 0.06 mm/s, p = 0.026). Conclusively, super-resolution ultrasound imaging makes it possible to detect and differentiate microbubble velocity responses to prazosin simultaneously in the renal cortical and medullary vascular beds.

Calibration of a focused passive cavitation detector using bubble shock waves

In microbubble-mediated therapeutic ultrasound, a focused passive cavitation detector (PCD) is often used to measure the bubbles’ acoustic emissions, providing useful signals for treatment monitoring. However, calibrating a spherically focused PCD is challenging, due to the difficulty of generating a spherical wave that matches the PCD’s surface curvature. Here, a PCD was calibrated using broadband shock waves generated by inertial collapses of single microbubbles. Microbubbles were diluted to a very low concentration, flowed through a wall-less gel channel, and sonicated using single-cycle, 0.5-MHz-centre-frequency, 1-MPa acoustic pulses. The focused PCD to be calibrated and a reference needle hydrophone captured their emissions. The sensitivity and phase response of the PCD relative to the reference hydrophone was calculated from the single bubble signals. For comparison, the PCD was also calibrated using a focused emitter as a sound source (Rich and Mast, JASA, 2015). The nominal PCD sensitivities obtained using the two methods agreed within 1% ± 14% within the PCD’s bandwidth (2–10 MHz). The calibration data from the bubble method was then used to correct the PCD’s signal distortions. Our method recovered the impulse waveform of the bubble-generated shock wave from the raw PCD signal, where such a waveform was not previously observed.

Laser-Induced Plasmonic Nanobubbles and Microbubbles in Gold Nanorod Colloidal Solution.

In this work, we studied the initiated plasmonic nanobubbles and the follow-up microbubble in gold nanorod (GNR) colloidal solution induced by a pulsed laser. Owing to the surface plasmon resonance (SPR)-enhanced photothermal effect of GNR, several nanobubbles are initiated at the beginning of illumination and then to trigger the optical breakdown of water at the focal spot of a laser beam. Consequently, microbubble generation is facilitated; the threshold of pulsed laser energy is significantly reduced for the generation of microbubbles in water with the aid of GNRs. We used a probing He-Ne laser with a photodetector and an ultrasonic transducer to measure and investigate the dynamic formations of nanobubbles and the follow-up microbubble in GNR colloids. Two wavelengths (700 nm and 980 nm) of pulsed laser beams are used to irradiate two kinds of dilute GNR colloids with different longitudinal SPRs (718 nm and 966 nm). By characterizing the optical and photoacoustic signals, three types of microbubbles are identified: a single microbubble, a coalesced microbubble of multiple microbubbles, and a splitting microbubble. The former is caused by a single breakdown, whereas the latter two are caused by discrete and series-connected multiple breakdowns, respectively. We found that the thresholds of pulsed energy to induce different types of microbubbles are reduced as the concentration of GNRs increases, particularly when the wavelength of the laser is in the near-infrared (NIR) region and close to the SPR of GNRs. This advantage of a dilute GNR colloid facilitating the laser-induced microbubble in the NIR range of the bio-optical window could make biomedical applications available. Our study may provide an insight into the relationship between plasmonic nanobubbles and the triggered microbubbles.

Effect of electrolyzed water and carbon dioxide microbubbles on removal of diazinon and diazoxon

AbstractEffect of electrolyzed water (EW) produced from sodium chloride solution in a single vessel and carbon dioxide microbubbles (CO2MB) on decomposition of diazinon and its oxidized product, diazoxon, was investigated. Furthermore, these removal by the EW with CO2MB from broccoli‐attached diazinon was examined. Diazinon was oxidized to diazoxon by EW, and the oxidative effect increased with increasing EW concentration from 0.1 to 0.6 mol L−1 or electrolyzing time from 1 to 10 min. However, EW concentration more than 0.2 mol L−1 was required to reduce diazoxon. The effect of EW on the decomposition of diazoxon increased with increasing EW concentration, electrolyzing time or reaction time from 10 to 60 min but decreased by generating CO2MB. Furthermore, diazinon concentration in broccoli was significantly decreased by treatment with deionized water or EW for 10 min, and the removal effect was continued by generating CO2MB in EW until 60 min. The diazoxon concentration in broccoli treated by EW decreased after increased up to 30 min, and the removal effect was increased by generating CO2MB. Also, the pH and available chlorine concentration (ACC) of the EW increased with increasing EW concentration or electrolyzing time but decreased and almost unchanged by generating CO2MB, respectively. Therefore, it was revealed that EW had a decomposition effect on diazinon and diazoxon and that CO2MB promoted the effect of EW on the removal of these pesticides in broccoli. Additionally, the decomposition effect of EW on diazinon and diazoxon was suggested to be influenced by high pH and ACC.Practical ApplicationThe EW produced from NaCl solution in a single vessel is a safer technique easy to be used than that from HCl. In addition, CO2MB has no harmful effects on the human body. This study demonstrated that the EW was effective for decomposing diazinon, an organophosphorus insecticide, and diazoxon, its oxidized product, and that the removal of these pesticides in broccoli by the EW could be more effectively achieved by generating CO2MB. Therefore, the use of EW with CO2MB can be expected to remove pesticides from fruits and vegetables at food factory.