Meifang Zhou

Ultrasound assisted photocatalytic degradation of diclofenac in an aqueous environment.

Diclofenac (DF) is an anti-inflammatory drug found in aqueous environments as a pollutant due to its widespread use. The sonolytic, photocatalytic and sonophotocatalytic degradation of DF using three photocatalysts (TiO(2), ZnO and Fe-ZnO) were studied. The degradation of DF followed first-order like kinetics. The sonophotocatalytic degradation using TiO(2) under UV-vis radiation showed a slight synergistic enhancement in the degradation of the parent compound, whereas a detrimental effect was observed for the mineralization process. In the case of Fe-ZnO, both degradation and mineralization showed near additive effects. A number of degradation products were identified.

The Design of Multifunctional Microbubbles for Ultrasound Image-Guided Cancer Therapy

Gas-filled microbubbles are widely used in diagnostic imaging. Recent developments have greatly enhanced the potential use of microbubbles for both diagnostic and therapeutic applications. For the potential use of microbubbles in therapeutic applications, the chemical nature of the shell and its mechanical properties are crucial, and requires a tailored synthetic approach. This review describes methods of preparation, mechanism of action, in vitro and in vivo stability and structural/functional characterization of microbubbles. New mechanisms for ultrasound-enhanced local drug and gene delivery are reviewed. Different strategies used to target microbubbles to regions of disease and some of the recent experiences in ultrasound image-guided therapy are discussed.

Tailoring the properties of ultrasonically synthesised microbubbles

Air-filled lysozyme microbubbles can be synthesized in an aqueous medium by emulsification followed by the cross-linking of protein molecules under high-intensity ultrasound. Here, we report on the tailoring of the properties of the ultrasonically synthesised microbubbles using new procedures. The efficiency of formation, size, size distribution and morphology of the microbubbles were controlled by manipulating the experimental conditions, namely, the sonication power and the length of sonication. An increase in the sonication time and power led to the formation of larger microbubbles with a broader size distribution. The microbubble shell thickness was found to decrease with an increase in the sonication power and time. Furthermore, a pulsed sonoluminescence technique was used to study the strength and stability of the microbubbles. The experimental results have shown that the effects of sonication time and power on the properties of the microbubbles are quite complex. A simple graphical matrix has been derived to obtain stable microbubbles with a narrow size distribution.

One-pot ultrasonic synthesis of multifunctional microbubbles and microcapsules using synthetic thiolated macromolecules

A one-pot ultrasonic procedure has been developed as a versatile route for synthesizing polymer-coated microspheres that have potential application as drug delivery vehicles. The use of synthetic thiolated poly(methacrylic acid) macromolecules as the shell material offers control over size, morphology and functionality of the microspheres.

Sonochemical and sustainable synthesis of graphene-gold (G-Au) nanocomposites for enzymeless and selective electrochemical detection of nitric oxide

In this study, a sonochemical approach was utilised for the development of graphene-gold (G-Au) nanocomposite. Through the sonochemical method, simultaneous exfoliation of graphite and the reduction of gold chloride occurs to produce highly crystalline G-Au nanocomposite. The in situ growth of gold nanoparticles (AuNPs) took place on the surface of exfoliated few-layer graphene sheets. The G-Au nanocomposite was characterised by UV-vis, XRD, FTIR, TEM, XPS and Raman spectroscopy techniques. This G-Au nanocomposite was used to modify glassy carbon electrode (GCE) to fabricate an electrochemical sensor for the selective detection of nitric oxide (NO), a critical cancer biomarker. G-Au modified GCE exhibited an enhanced electrocatalytic response towards the oxidation of NO as compared to other control electrodes. The electrochemical detection of NO was investigated by linear sweep voltammetry analysis, utilising the G-Au modified GCE in a linear range of 10-5000μM which exhibited a limit of detection of 0.04μM (S/N=3). Furthermore, this enzyme-free G-Au/GCE exhibited an excellent selectivity towards NO in the presence of interferences. The synergistic effect of graphene and AuNPs, which facilitated exceptional electron-transfer processes between the electrolyte and the GCE thereby improving the sensing performance of the fabricated G-Au modified electrode with stable and reproducible responses. This G-Au nanocomposite introduces a new electrode material in the sensitive and selective detection of NO, a prominent biomarker of cancer.

Antimicrobial and Biosensing Ultrasound-Responsive Lysozyme-Shelled Microbubbles

Air-filled lysozyme microbubbles (LSMBs) were engineered as a support for the immobilization of gold nanoparticles and an enzyme, alkaline phosphatase, in order to develop micro-antimicrobial and biosensing devices. Gold nanoparticles immobilized on LSMBs significantly improved the antimicrobial efficacy of the microbubbles against M. lysodeikticus. The surface functionalization of the microbubbles with gold nanoparticles did not affect their echogenicity when exposed to an ultrasound imaging probe. Alkaline phosphatase was conjugated on the surface of microbubbles without compromising its enzymatic activity. The functionalized microbubbles were used for the detection of paraoxon in aqueous solutions.

Defect chemistry and semiconducting properties of calcium titanate

The present paper considers the effect of oxygen partial pressure on the presence of point defects in calcium titanate (CaTiO3) at elevated temperatures at which a gas/solid equilibrium is reached. Defect models of undoped (CaTiO3) are considered within several regimes of oxygen partial pressures involving (i) extremely reducing conditions, (ii) reducing conditions, and (iii) oxidizing conditions, which are described by different charge-neutrality conditions. The mechanism of donor incorporation is considered in terms of both ionic and electronic charge compensation. It is shown that electronic and ionic charge compensations prevail at low and high p(O2), respectively.

Correlation between sonochemistry and sonoluminescence at various frequencies

The development of generic large-scale sonochemical reactors requires a fundamental understanding of how various experimental parameters affect the acoustic cavitation efficiency. With a view to expand the experimental database and knowledge, the changes to acoustic cavitation bubble structures, caused by covering the air–solution interface with a lid at various frequencies and power levels, have been investigated. The accompanying effects have been quantified using sonochemiluminescence and sonoluminescence as probes. It has been observed that the chemically active cavitation bubble population is dominant in the “open” (without lid) configuration and the sonoluminescing bubble population is dominant in the “closed” (with lid) configuration. A possible reason for such differences is the existence of a well-defined standing wave pattern in the closed system.

Ultrasonic fabrication of TiO2/chitosan hybrid nanoporous microspheres with antimicrobial properties

We report a sonochemical method for the fabrication of stable TiO2–chitosan hybrid microspheres possessing nanoporous structure and antimicrobial properties. The microspheres were characterized by evaluating their size, surface morphology, and ultrasound-triggered release of encapsulated materials. The size range of the microspheres was found to be in the range 2–20 μm. The antimicrobial activity of TiO2/chitosan microspheres was also evaluated. A possible mechanism for the formation of TiO2-encapsulated chitosan microspheres has been proposed. The methodology demonstrated here can be extended to fabricating nanoparticle or liquid delivery vectors and density controlled catalysts for applications in catalytic and biomedical areas.

A comparison of the physical properties of ultrasonically synthesized lysozyme- and BSA-shelled microbubbles.

Ultrasonic technique has been used for synthesising protein microspheres possessing specific physical and functional properties. Various proteins have been used as shell materials under different experimental conditions. In previous studies, thermal or chemical denaturation of the proteins was used to obtain stable bovine-serum albumin (BSA) and lysozyme microbubbles (MBs), respectively. It is ideal to establish a generic procedure to synthesise microspheres irrespective of the nature of the protein. In order to see if a generic procedure can be established, ultrasonic synthesis of lysozyme and BSA MBs was carried out under similar experimental conditions and their properties were evaluated. The size, size distribution and the stability of the MBs were significantly different for the lysozyme and BSA MBs. The size and size distribution of the lysozyme coated MBs were larger than BSA bubbles. The mechanical strength of MBs against the shear forces, generated when irradiated by high frequency ultrasound, was studied using pulsed-sonoluminescence (SL). This study indicated that lysozyme MBs were significantly more stable than BSA MBs. An increase in mechanical strength of the MBs may lead to an increase in their storage lifetime and stability against gas diffusion. Possible reasons for such observations have been discussed.