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Introduction: Dual-frequency ultrasound has recently been shown to extensively enhance the acoustic cavitation yield in water. Methods: In this study, the in vivo antitumor effect of simultaneous, dual-frequency ultrasound at low-level intensity ( I = 2 W/cm for 1 MHz and I = 0.2 W/cm for 150 kHz) in combination with an intravenous injection of 5 mg/kg hematoporphyrin (Hp) was investigated in a model of breast adenocarcinoma in Balb/c mice. Seventy-one tumor-bearing mice were divided into nine treatment groups: control, sham, Hp injection, and single- and dual-frequency sonication in the presence and absence of Hp. The tumor growth delay was then calculated based on the tumor volume at various times after treatment using the following parameters: relative volume percent, $$ T_{5} $$ and $$ T_{2} $$ times (to reach five and two times the initial volume), percent of tumor growth inhibition ratio, and survival period. Results: Our results showed no significant difference between the 150 kHz and 1 MHz single-frequency groups when compared with the sham group after 9 days of treatment ( p > 0.05). However, treatment with dual-frequency ultrasound significantly delayed tumor growth when compared with the sham group ( p < 0.05) after 9 days of treatment. Furthermore, in vivo experiments showed that combined dual-frequency sonication controlled tumor growth more effectively than single-frequency sonication. Evaluation of the therapeutic effects of single- and dual-frequency ultrasound in sonodynamic therapy revealed that treatment with the combination of dual-frequency ultrasound and Hp resulted in a significant reduction in the relative volume percent of tumors after 3 days of treatment ( p < 0.05) compared with the controls. Additionally, the T time and the survival period in the group treated with the combination therapy was significantly longer than those in all the other groups ( p < 0.05). These findings were further verified histopathologically. Conclusion: In conclusion, our results reveal that sonodynamic therapy using dual-frequency ultrasound is able to extend the survival time of animals compared with single-frequency sonication. [ABSTRACT FROM AUTHOR]

Background: Most bone ultrasound devices are designed for through-transmission measurements of the calcaneus. In principle, ultrasound backscattering measurements are possible at more typical fracture sites of the central skeleton. Unfortunately, soft tissue overlying the bones diminishes reliability of these measurements. Purpose: To apply the single-transducer dual-frequency ultrasound (DFUS) technique to eliminate the errors induced by soft tissue on the measurements of integrated reflection coefficient (IRC) in human distal femur in vivo. Material and Methods: Ultrasound and dual-energy X-ray absorptiometry (DXA) examinations were conducted on a bodybuilder during a 21-week training and dieting period. Results: Significant changes in quantity and composition of soft tissue took place during the diet. However, DXA measurements showed no significant effects on bone density measurements. The single transducer DFUS technique enabled the determination of local soft-tissue composition, as verified by comparison with the DXA (r=0.91, n=8, p<0.01). Further, the technique eliminated the soft-tissue-induced error from IRC measured for the bone. The uncorrected IRC associated significantly with the change in local soft-tissue composition (r=-0.83, n=8, p<0.05), whereas the corrected IRC values showed no significant dependence (r=-0.30, n=8, p=0.46) on local soft-tissue composition. Conclusion: The DFUS technique may significantly enhance the accuracy of clinical ultrasound measurements of bone. [ABSTRACT FROM AUTHOR]

The influences of the ultrasound frequency and pretreatment duration on the viscoelastic properties and microstructure of whey protein emulsion gels (WPEG) were investigated using dual-frequency ultrasound in sequential mode. And the effect of ultrasound modification of whey protein on the in vitro digestion of WPEG was assessed. The results showed that ultrasonic pretreatment could improve the viscoelastic properties and microstructure of WPEG. WPEG pretreated with an ultrasound sequence of 20 and 28 kHz for 10 min exhibited better storage modulus (G′) and microstructure compared to the control. The final G′ and final tanδ of WPEG increased by 184% and 8% respectively compared with the control. CLSM and SEM showed that ultrasound pretreatment could result in the formation of a compact and fine network. The ultrasound pretreatment improved the digestion of WPEG by enhancing the acid and base consumption during gastric and intestinal digestion, respectively. It was suggested that dual-frequency ultrasound in sequential mode could influence the fate of WPEG during gastrointestinal digestion by changing the microstructure of WPEG. Dual-frequency ultrasound could potentially be used to develop foods with new nutritional properties. [Display omitted] • Sequential dual frequency ultrasound (DFU) pretreatment enhanced G′ and tanδ of whey protein emulsion gels (WPEG). • Sequential DFU pretreatment improve the digestive rate of WPEG. • The microstructure of WPEG might influence their fate during digestion. [ABSTRACT FROM AUTHOR]

Ultrasound (US) can be employed to activate persulfate (PS) for degrading total petroleum hydrocarbons (TPH). In this study, to improve the degradation efficiency, PS is combined with dual-frequency US (DFUS) towards synergistic degradation of TPH in real soil. After 180 min, the degradation percentages for DFUS/PS, DFUS, high-frequency US and high-frequency US/PS are around 88.9%, 38.7%, 7.3% and 54.2%, respectively. Additionally, the influence of US power, PS content, slurry pH and temperature, and TPH components on the degradation percentage in the DFUS/PS process are explored. Scanning electron microscopy (SEM) images and the results of specific surface area verify that the DFUS can break the soil aggregates more effectively than the single-frequency US, and thus enhance the TPH desorption and accelerate the oxidant diffusion. Moreover, the investigation of the mechanism is further evaluated through quenching and electron spinning resonance spectrum (ESR) tests. The results indicate that the generation of SO 4 − and OH in DFUS/PS is ~1.6 times and ~2.5 times as much, respectively, as in high frequency US/PS. The relative contributions to the synergistic TPH degradation in the DFUS/PS system are: SO 4 − (PS activation via the heat induced by US) > pyrolysis inside the bubbles (hydrophobicity of TPH) > SO 4 − (PS activation via US cavitation) > OH. Finally, the hypothesis is confirmed via the evaluation of the degradation kinetics, which shows that the combined process of DFUS/PS is not a simple addition of the US and PS, but provides a highly effective process of synergistic degradation. Unlabelled Image • DFUS/PS is efficient for high-lever TPH degradation in real soil (~88.9%). • DFUS smashes the soil aggregates more effectively than single-frequency US. • DFUS/PS generates more radicals (SO 4 − and OH) than single-frequency US/PS. • SO 4 − (PS thermal activation from US) is mainly responsible for TPH degradation. [ABSTRACT FROM AUTHOR]

• Ultrasound was used to inhibit formation of Lysinoalanine (LAL) in rice protein. • Sequential dual-frequency ultrasound of 20/40 kHz exhibited best inhibition effect. • Strong correlation between free sulfhydryl and LAL content was observed. • Reduction in LAL could be associated with changes in the structure of rice protein. The effect of dual-frequency ultrasound treatment with different working modes on the lysinoalanine (LAL) formation and structural characterization of rice dreg protein isolates (RDPI) was studied during alkaline exaction processing. Ultrasonic notably decreased the LAL amount of RDPI and enhanced the protein dissolution rate. The LAL content of RDPI, especially sequential dual frequency 20/40 kHz, decreased by 12.02% (P < 0.05), compared to non-sonicated samples. Herein, the protein dissolution rate was higher. The changes in sulfhydryl groups was positively correlated with the LAL formation. The amino acids (AA) such as threonine (Thr), lysine (Lys), and arginine (Arg) were reduced, resulting in a decrease in LAL content following sonication. Besides, ultrasonication altered protein secondary structure by reducing random coil and β-sheet contents, while α-helix and β-turn contents increased. Alterations in the surface hydrophobicity, particle size, particle size distribution, and microstructure indicated more irregular fragment with microparticles of RDPI by sonochemical treatment. Thus, ultrasound treatment may be a new and efficacious process for controlling the LAL generation in prepared-protein food(s) during alkali extraction. [ABSTRACT FROM AUTHOR]

Since the early 2000s, dual-frequency ultrasound (DFUS) has received much attention for synergistically enhanced elimination of organic pollutants and pathogenic microorganisms from water. In the present review, we have surveyed recent developments in acoustic physics to elucidate the mechanism of synergistic effect under exposure of aqueous media to DFUS. Briefly, the nonlinear dynamics of microbubbles upon DFUS exposure produces additional frequencies, such as harmonics, subharmonics, ultraharmonics and combination frequencies. These increase the probability of bubbles collapse, thereby enhancing cavitation and generating more reactive oxygen species (ROS) for advanced oxidation processes (AOPs). Further, literature data on ROS generation, chemical degradation and microbial inactivation in aqueous media through DFUS alone and DFUS-based AOPs (involving oxidants or catalysts) have been discussed. In this regard, optimal frequency combination, sonoreactor type and transducer arrangement appear to be key parameters for achieving a high synergistic effect. Strengths and shortcomings of DFUS to water treatment and disinfection have been identified and future research directions have been proposed. Though most studies were conducted on pure (matrix-free) aqueous solutions, these AOPs could be applicable for treating real waters. Image 1 • Mechanism of synergistic effect under dual frequency ultrasound (DFUS) is elucidated. • Frequency combination, sonoreactor type and transducer arrangement are key issues. • Studies on organic degradation and microbial inactivation by DFUS are reviewed. • Inactivation processes by DFUS are scarcely studied and need further research. • Research on degradation and inactivation in real waters is required. [ABSTRACT FROM AUTHOR]

• US equipment typically used in a common laboratory can degrade PFAS. • DFUS/PS is efficient for PFAS defluorination, particularly for PFOA (~100%). • DFUS/PS process can efficiently degrade PFAS in the contaminated soil. • Degradation pathways and kinetics of PFOA are studied. Ultrasound (US) can degrade per- and polyfluoroalkyl substances (PFAS) by the cavitation or pyrolysis effect. In this study, we find that the US equipment typically used in a common laboratory, such as 20 kHz and 43 kHz for cleaning or homogenisation, can degrade PFAS, although the process is slow (with approximately 14.6% and 20.1% defluorination after 6 h, respectively). To accelerate the degradation process, a dual-frequency US is combined with persulfate (PS) to synergistically degrade PFAS in water and soil. Typical PFAS including perfluorooctanoic acid (PFOA), perfluorooctane sulfonate (PFOS) and 1H, 1H, 2H, 2H-perfluorooctanesulfonic acid (6:2 FTS) are used to evaluate the degradation performance of dual-frequency US/PS in water. After 6 h of degradation, the defluorination percentage is, from highest to lowest, PFOA (100 ± 1.2%) > 6:2 FTS (86.9 ± 0.9%) > PFOS (46.5 ± 1.0%). Interestingly, the dual-frequency US/PS process can also efficiently degrade PFAS in the contaminated soil, with a 62–71% degradation of 14 PFAS (28 is the maximum number of PFAS that can be quantitatively monitored), representing an encouraging progress. Finally, the degradation pathways and kinetics of PFOA are studied by monitoring the degradation intermediates, and by indicating the combination of the dual-frequency US/PS is not simply addition with each other, but with a synergistic effect of degradation. [ABSTRACT FROM AUTHOR]

The objectives of this study were to investigate the changes in the aggregation and emulsifying properties of soy protein isolate (SPI) pretreated with dual-frequency ultrasound and three different ionic liquids (ILs), tributyl methyl ammonium chloride ([TBMA]Cl), 1-butyl-3-methyl imidazolium chloride ([BMIM]Cl) and 1-butyl-3-methyl imidazolium tetrafluoroborate ([BMIM]BF 4). Results showed that dual-frequency ultrasound and ILs could not change the primary structure of SPI. The changes in UV–vis spectra indicated the unfolding of SPI as pretreated by [TBMA]Cl and [BMIM]Cl combined with dual-frequency ultrasound, followed by formation of soluble aggregates. The thermal stability analysis of the regenerated SPI suggested that [BMIM]BF 4 presumably broke most of the hydrogen bonds within adjacent SPI molecules, leading to the decrease of thermal stability. Transmission electron microscopy showed major changes in protein morphology upon protein–protein interactions. SPI emulsion pretreated with dual-frequency ultrasound and [BMIM]BF 4 had a higher emulsion stability index than the other samples (P < 0.05). Furthermore, as compared to untreated protein, all ultrasound and ILs pretreatments decreased the creaming index of SPI emulsion. These results indicated that combination of dual-frequency ultrasound and ionic liquids could be a potential method to change the aggregation and emulsifying properties of SPI. • Dual-frequency ultrasound and ILs changed the aggregation of SPI. • Large aggregates were formed by dual-frequency ultrasound and [BMIM]BF 4 treatment. • Stability of emulsions were improved by appropriate ILs and ultrasound. [ABSTRACT FROM AUTHOR]

• Continuous particle synthesis in a dual-frequency ultrasound microreactor. • Novel application mode of switching between low- and high-frequency ultrasound. • Synergistic effects of low-frequency cavitation and high-frequency acoustophoresis. • Dual-frequency ultrasound results in particles with a narrow size distribution. • High ultrasound energy efficiency and temperature control is achieved. Ultrasound (US) is a promising method to address clogging and mixing issues in microreactors (MR). So far, low frequency US (LFUS), pulsed LFUS and high frequency US (HFUS) have been used independently in MR for particle synthesis to achieve narrow particle size distributions (PSD). In this work, we critically assess the advantages and disadvantages of each US application method for the case study of calcium carbonate synthesis in an ultrasonic microreactor (USMR) setup operating at both LFUS (61.7 kHz, 8 W) and HFUS (1.24 MHz, 1.6 W). Furthermore, we have developed a novel approach to switch between LFUS and HFUS in an alternating manner, allowing us to quantify the synergistic effect of performing particle synthesis under two different US conditions. The reactor was fabricated by gluing a piezoelectric plate transducer to a silicon microfluidic chip. The results show that independently applying HFUS and LFUS produces a narrower PSD compared to silent conditions. However, at lower flow rates HFUS leads to agglomerate formation, while the reaction conversion is not enhanced due to weak mixing effects. LFUS on the other hand eliminates particle agglomerates and increases the conversion due to the strong cavitation effect. However, the required larger power input leads to a steep temperature rise in the reactor and the risk of reactor damage for long-term operation. While pulsed LFUS reduces the temperature rise, this application mode leads again to the formation of particle agglomerates, especially at low LFUS percentage. The proposed application mode of switching between LFUS and HFUS is proven to combine the advantages of both LFUS and HFUS, and results in particles with a unimodal narrow PSD (one order of magnitude reduction in the average size and span compared to silent conditions) and negligible rise of the reactor temperature. [ABSTRACT FROM AUTHOR]