A Microstructural Study of the O/W Primary Emulsion on the Formation of Oil-in-Water-in-Oil Multiple Emulsion.

AIM: This study aimed to investigate the influence of the preparation process and composition on the microstructure of the O/W primary emulsions and the corresponding impact on the formation of oil-in-water-in-oil (O/W/O) multiple emulsions. OBJECTIVES: Multiple emulsions were prepared by a two-step emulsification method and the microstructure was characterized by the microscope. METHODS: The primary emulsion was prepared by four kinds of preparation methods, which include both high-energy and low-energy emulsification, and then the primary emulsion was re-emulsified by stirring in the outer phase. RESULT: Through the theoretical investigation and the corresponding verification experiments of the interfacial film, the geometric reason for O/W/O multiple emulsion which was relatively difficult to prepare has been found. The microstructure of O/W particles was more obvious, and the particle size became smaller with the increase of the hydrophilic emulsifier amount beneficial to the formation and stability of O/W/O structures. However, the excess emulsifier that existed in the water phase could interfere the stability of the W/O interface. Moreover, the viscosity of inner oil phase had a large influence on the formation of O/W/O emulsion by affecting the particle size of the primary emulsion and the dynamic equilibrium between the inner and outer oil phase. CONCLUSION: It can be concluded that fine multiple emulsions were formed when the particle size of the primary emulsion was moderate since the large particles would break through the outer interface membrane and small particles would combine with the outer oil phase due to the Ostwald ripening.

Target capturing performance of microfluidic channel surface immobilized aptamers: the effects of spacer lengths.

Aptamers have been widely used to recognize and capture their targets in sensitive detection applications, such as in detections of circulating tumor cells. In this study, we investigate the effects of different lengths of oligo-T spacers on surface tethered sgc8 aptamers and their target capturing performances. To achieve this, sgc8 aptamers were immobilized onto microfluidic channel surfaces via oligo-T spacers of different lengths, and the target capturing performances of these immobilized aptamers were studied using CCRF-CEM cells. We demonstrate that the capturing performances of the immobilized aptamers were significantly affected by steric hindrance. Our results also show that aptamers immobilized on surfaces via spacers of ten Ts demonstrated the best cell capturing performances; aptamers with either too short or too long oligo-T spacers showed reduced cell capturing performances. Therefore it can be concluded that spacer optimizations are critically important for surface tethered aptamers that are commonly used in microfluidic devices for sensitive target sensing and detections.

Aptamer surface functionalization of microfluidic devices using dendrimers as multi-handled templates and its application in sensitive detections of foodborne pathogenic bacteria.

A microfluidic system that incorporates both dendrimers and aptamers to detect E. coli O157:H7 is developed. To achieve this, generation 7-polyamidoamine dendrimers were immobilized onto the detection surfaces of PDMS microfluidic channels; subsequently aptamers against E. coli O157:H7 were conjugated onto the microchannel surfaces via the immobilized dendrimers as templates. Surface modifications were characterized by FTIR, XPS, water contact angles, fluorescence microscopy and AFM to confirm the success of each surface modification steps. The efficacy of this simple microchannel in detection was investigated using E. coli O157:H7 spiked samples. Our results showed that this interesting approach significantly increased the amount of aptamers available on the microfluidic channel surfaces to capture E. coli O157:H7 cells to allow sensitive detection, which in turn resulted in detections of E. coli O157:H7 cells at a low limit of detection of 102 cells mL-1. The results also demonstrated that in comparison with the generation 4-polyamidoamine dendrimers (G4) modified microchannels, those modified with G7 showed enhanced detection signals, improved target capturing efficiencies, and at higher throughput. This simple whole cell detection design has not been reported in the literature and it is an interesting and effective approach to developing a sensitive and rapid detection platform for foodborne pathogenic bacteria.

Development of multifunctional nanoparticles towards applications in non-invasive magnetic resonance imaging and axonal tracing.

A multifunctional nanobiomaterial has been developed by deliberately combining functions of superparamagnetism, fluorescence, and axonal tracing into one material. Superparamagnetic iron oxide nanoparticles were first synthesized and coated with a silica layer to prevent emission quenching through core-dye interactions; a fluorescent molecule, fluorescein isothiocyanate, was doped inside second layer of silica shell to improve photo-stability and to enable further thiol functionalization. Subsequently, biotinylated dextran amine, a sensitive axonal tracing reagent, was immobilized on the thiol-functionalized nanoparticle surfaces. The resulting nanoparticles were characterized by transmission electron microscopy, dynamic light scattering, X-ray diffraction, X-ray photoelectron spectroscopy, UV-Vis spectroscopy, magnetic resonance imaging and fluorescence confocal microscopy. In vitro cell experiments using both undifferentiated and differentiated Neuro-2a cells showed that the cells were able to take up the nanoparticles intracellularly and that the nanoparticles showed good biocompatibilities. In summary, this new material demonstrated promising performances for both optical and magnetic resonance imaging modalities, suggesting its promising potentials in applications such as in non-invasive imaging, particularly in neuronal tracing.

Facile synthesis of Gd-doped CdTe quantum dots with optimized properties for optical/MR multimodal imaging.

Each imaging modality has its own merits and intrinsic limitations; therefore, combining two or more complementary imaging modalities has become an interesting area of research. Recently, magnetic ion-doped quantum dots have become an increasingly promising class of optical/magnetic resonance multimodal imaging probes due to their excellent physical and chemical properties. In this work, Gd-doped CdTe quantum dots (QDs) were successfully synthesized via a facile one-step refluxing route,and their optimal synthesis conditions were investigated. The prepared CdTe:Gd QDs were shown to exhibit good optical properties with high quantum yields up to 69%, high longitudinal relaxivity (r 1 = 3.8 mM-1 s-1), and good crystalline structures. In addition, after further QD surface modification with dextran amine (DA), the resulting DA-modified QDs (i.e. DA-CdTe:Gd QDs) showed strong magnetic resonance imaging contrast (r 1 = 3.5 mM-1 s-1) and improved biocompatibility when tested with cell cultures in vitro. Taken together, this new material demonstrated promising performances for both optical and magnetic resonance imaging modalities, suggesting its promising potential applications in non-invasive imaging, particularly in neuronal tracing.

Developing a non-fouling hybrid microfluidic device for applications in circulating tumour cell detections.

Non-specific cell adsorption is a challenge in sensitive detections using microfluidic systems, such as detecting circulating tumour cells from blood samples. In this report, we present a new strategy to study the combined effects of surface hydrophilicity/hydrophobicity, electric charges and roughness on surface non-fouling properties of a PDMS/SU-8 microfluidic system. To achieve this, microchannel surfaces were modified by poly(amidoamine) generation 4 and generation 7, dendrimers that rendered surfaces negatively and positively charged at pH 7.4, respectively. Water contact angle, atomic force microscopy (AFM) and microscopy were used to characterize and confirm surface modifications, and the non-fouling performance of the resulting surfaces was tested using both live and dead CCRM-CEM cancer cells. Our results show that for live cells, electric charges of a surface is the most important factor affecting the non-fouling features of the surface in microfluidic systems; in contrast, for dead cells, surface hydrophilicity is the most important factor affecting surface non-fouling properties. However, surface roughness does not seem to be as important for both live and dead cells under the experimental conditions used in this study. These results also highlight the importance of different considerations when designing a lab-on-a-chip microfluidic system for high sensitivity biosensing and detection applications.

Developing an ultra non-fouling SU-8 and PDMS hybrid microfluidic device by poly(amidoamine) engraftment.

A new strategy to prepare an ultra non-fouling SU-8/poly(dimethylsiloxane) (PDMS) hybrid microfluidic system is presented. We report a simple method to bond both SU-8 and PDMS surfaces to prepare the hybrid microfluidic device and then simultaneously modify both SU-8 and PDMS surfaces using poly(amidoamine) (PAMAM), a highly hydrophilic dendrimer to enhance non-fouling properties of the hybrid microfluidic channel. Water contact angle, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) are used to characterize and confirm surface modifications. Finally the non-fouling performance of the resulting microfluidic system is tested using both microbeads and Escherichia coli O157:H7 bacterial cells. We demonstrate that the obtained hybrid microfluidic system shows a significant microbead adsorption suppression of 99.7%, an ultra non-fouling performance that has not been reported in the literature before; in addition, 95% bacteria surface adsorption suppression is also obtained. Considering the significantly improved non-fouling performance and the ease of preparing the hybrid microfluidic system, we anticipate that this strategy will find wide applications in biosensing and detection.