Synthesis and active manipulation of magnetic liquid beads.

We report the fabrication and characterisation of magnetic liquid beads with a solid magnetic shell and liquid core using microfluidic techniques. The liquid beads consist of a fluorinated oil core and a polymer shell with magnetite particles. The beads are generated in a flow-focusing polydimethylsiloxane (PDMS) device and cured by photo polymerisation. We investigated the response of the liquid beads to an external magnetic field by characterising their motion towards a permanent magnet. Magnetic sorting of liquid beads in a channel was achieved with 90% efficiency. The results show that the liquid beads can be controlled magnetically and have potential applications in digital microfluidics including nucleic acid amplification, drug delivery, cell culture, sensing, and tissue engineering. The present paper also discusses the magnetophoretic behaviour of the liquid bead by varying its mass and magnetite concentration in the shell. We also demonstrated the two-dimensional self-assembly of magnetic liquid beads for potential use in digital polymerase chain reaction and digital loop mediated isothermal amplification.

Microfluidic encapsulation of DNAs in liquid beads for digital PCR application.

Droplet-based microfluidics and digital polymerase chain reaction (PCR) hold significant promise for accurately detecting and quantifying pathogens. However, existing droplet-based digital PCR (ddPCR) applications have been relying exclusively on single emulsion droplets. Single emulsion droplets may not be suitable for applications such as identifying the source and pathways of water contamination where the templates must be protected against harsh environmental conditions. In this study, we developed a core-shell particle to serve as a protective framework for DNAs, with potential applications in digital PCR. We employed a high-throughput and facile flow-focusing microfluidic device to generate liquid beads, core-shell particles with liquid cores, which provided precise control over process parameters and consequently particle characteristics. Notably, the interfacial interaction between the core and shell liquids could be adjusted without adding surfactants to either phase. As maintaining stability is essential for ensuring the accuracy of digital PCR (dPCR), we investigated parameters that affect the stability of core-shell droplets, including surfactants in the continuous phase and core density. As a proof of concept, we encapsulated a series of human faecal DNA samples in the core-shell droplets and the subsequent liquid beads. The core-shell particles ensure contamination-free encapsulation of DNA in the core. The volume of the core droplets containing the PCR mixture is only 0.12 nL. Our experimental results indicate that the liquid beads formulated using our technique can amplify the encapsulated DNA and be used for digital PCR without interfering with the fluorescence signal. We successfully demonstrated the ability to detect and quantify DNA under varying concentrations. These findings provide new insights and a step change in digital PCR that could benefit various applications, including the detection and tracking of environmental pollution.

Precise, wide field, and low-cost imaging and analysis of core-shell beads for digital polymerase chain reaction.

Digital droplet reactors have become a valuable tool for the analysis of single cells, organisms, or molecules by discretising reagents into picolitre or nanolitre volumes. However, DNA-based assays typically require processing of samples on the scale of tens of microlitres, with the detection of as few as one or as many as a hundred thousand fragments. Through the present work, we introduce a flow-focusing microfluidic device that produces 120 picolitre core-shell beads, which are assembled into a monolayer in a Petri dish for visualization and analysis. The bead assembly is subjected to polymerase chain reaction (PCR) amplification and fluorescence detection to digitally quantify the DNA concentration of the sample. We use a low-cost 21-megapixel digital camera and macro lens to capture wide-field fluorescence images with a 10-30 mm2 field-of-view at magnifications ranging from 5× to 2.5×. A customised Python script analysed the acquired images. Our study demonstrates the ability to perform digital PCR analysis of the entire bead assembly through end-point imaging and compare the results with those obtained through RT-qPCR.

Core-Shell Particles: From Fabrication Methods to Diverse Manipulation Techniques.

Core-shell particles are micro- or nanoparticles with solid, liquid, or gas cores encapsulated by protective solid shells. The unique composition of core and shell materials imparts smart properties on the particles. Core-shell particles are gaining increasing attention as tuneable and versatile carriers for pharmaceutical and biomedical applications including targeted drug delivery, controlled drug release, and biosensing. This review provides an overview of fabrication methods for core-shell particles followed by a brief discussion of their application and a detailed analysis of their manipulation including assembly, sorting, and triggered release. We compile current methodologies employed for manipulation of core-shell particles and demonstrate how existing methods of assembly and sorting micro/nanospheres can be adopted or modified for core-shell particles. Various triggered release approaches for diagnostics and drug delivery are also discussed in detail.

Fabrication and characterization of core-shell microparticles containing an aqueous core.

Core-shell microparticles containing an aqueous core have demonstrated their value for microencapsulation and drug delivery systems. The most important step in generating these uniquely structured microparticles is the formation of droplets and double emulsion. The droplet generator must meet the performance and reliability requirements, including accurate size control with tunability and monodispersity. Herein, we present a facile technique to generate surfactant-free core-shell droplets with an aqueous core in a microfluidic device. We demonstrate that the geometry of the core-shell droplets can be precisely adjusted by the flow rates of the droplet components. As the shell is polymerized after the formation of the core-shell droplets, the resulting solid microparticles ensure the encapsulation of the aqueous core and prevent undesired release. We then study experimentally and theoretically the behaviour of resultant microparticles under heating and compression. The microparticles demonstrate excellent stability under both thermal and mechanical loads. We show that the rupture force can be quantitatively predicted from the shell thickness relative to the outer shell radius. Experimental results and theoretical predictions confirm that the rupture force scales directly with the shell thickness.