Highly crosslinked poly(dimethylsiloxane) microbeads with uniformly dispersed quantum dot nanocrystals

Encapsulation of Cadmium-Free InP/ZnSe/ZnS Quantum Dots in Poly(LMA-co-EGDMA) Microparticles via Co-flow Droplet Microfluidics

Quantum dots (QDs) are semiconductor nanocrystals that are used in optoelectronic applications. Most modern QDs are based on toxic metals, for example Cd, and do not comply with the European Restriction of Hazardous Substances regulation of the European Union. Latest promising developments focus on safer QD alternatives based on elements from the III-V group. However, the InP-based QDs lack an overall photostability under environmental influences. One design path of achieving stability is through encapsulation in cross-linked polymer matrices with the possibility to covalently link the matrix to surface ligands of modified core-shell QDs. The work focuses on the formation of polymer microbeads suitable for InP-based QD encapsulation, allowing for an individual protection of QDs and an improved processibility via this particle-based approach. For this, a microfluidic based method in the co-flow regime is used that consists of an oil-in-water droplet system in a glass capillary environment. The generated monomer droplets are polymerized in-flow into poly(LMA-co-EGDMA) microparticles with embedded InP/ZnSe/ZnS QDs using a UV initiation. They demonstrate how a successful polymer microparticle formation via droplet microfluidics produces optimized matrix structures leading to a distinct photostability improvement of InP-based QDs compared to nonprotected QDs.

Engineering a macroporous oxygen-generating scaffold for enhancing islet cell transplantation within an extrahepatic site

Insufficient oxygenation is a serious issue arising within cell-based implants, as the hypoxic period between implantation and vascularization of the graft is largely unavoidable. In situ oxygen supplementation at the implant site should significantly mitigate hypoxia-induced cell death and dysfunction, as well as improve transplant efficacy, particularly for highly metabolically active cells such as pancreatic islets. One promising approach is the use of an oxygen generating material created through the encapsulation of calcium peroxide within polydimethylsiloxane (PDMS), termed OxySite. In this study, OxySite microbeads were incorporated within a macroporous PDMS scaffold to create a single, streamlined, oxygen generating macroporous scaffold. The resulting OxySite scaffold generated sufficient local oxygenation for up to 20 days, with nontoxic levels of reaction intermediates or by-products. The benefit of local oxygen release on transplant efficacy was investigated in a diabetic Lewis rat syngeneic transplantation model using a clinically relevant islet dosage (10,000 IEQ/kg BW) with different isolation purities (80%, 90%, and 99%). Impure islet preparations containing pancreatic non-islet cells, which are common in the clinical setting, permit examination of the effect of increased overall oxygen demand. Our transplantation outcomes showed that elevating the oxygen demand of the graft with decreasing isolation purity resulted in decreased graft efficacy for control implants, while the integration of OxySite significantly mitigated this impact and resulted in improved graft outcomes. Results highlight the superior clinical translational potential of these off-the-shelf OxySite scaffolds, where islet purity and the overall oxygen demands of implants are increased and highly variable. The oxygen-generating porous scaffold further provides a broad platform for enhancing the survival and efficacy of cellular implants for numerous other applications. STATEMENT OF SIGNIFICANCE: Hypoxia is a serious issue within tissue engineered implants. To address this challenge, we developed a distinct macroporous scaffold platform containing oxygen-generating microbeads. This oxygen-generating scaffold showed the potential to support clinically relevant cell dosages for islet transplantation, leading to improved treatment efficacy. This platform can also be used to mitigate hypoxia for other biomedical applications.

MRBLES 2.0: High-throughput generation of chemically functionalized spectrally and magnetically encoded hydrogel beads using a simple single-layer microfluidic device

The widespread adoption of bead-based multiplexed bioassays requires the ability to easily synthesize encoded microspheres and conjugate analytes of interest to their surface. Here, we present a simple method (MRBLEs 2.0) for the efficient high-throughput generation of microspheres with ratiometric barcode lanthanide encoding (MRBLEs) that bear functional groups for downstream surface bioconjugation. Bead production in MRBLEs 2.0 relies on the manual mixing of lanthanide/polymer mixtures (each of which comprises a unique spectral code) followed by droplet generation using single-layer, parallel flow-focusing devices and the off-chip batch polymerization of droplets into beads. To streamline downstream analyte coupling, MRBLEs 2.0 crosslinks copolymers bearing functional groups on the bead surface during bead generation. Using the MRBLEs 2.0 pipeline, we generate monodisperse MRBLEs containing 48 distinct well-resolved spectral codes with high throughput (>150,000/min and can be boosted to 450,000/min). We further demonstrate the efficient conjugation of oligonucleotides and entire proteins to carboxyl MRBLEs and of biotin to amino MRBLEs. Finally, we show that MRBLEs can also be magnetized via the simultaneous incorporation of magnetic nanoparticles with only a minor decrease in the potential code space. With the advantages of dramatically simplified device fabrication, elimination of the need for custom-made equipment, and the ability to produce spectrally and magnetically encoded beads with direct surface functionalization with high throughput, MRBLEs 2.0 can be directly applied by many labs towards a wide variety of downstream assays, from basic biology to diagnostics and other translational research.

Programmable Microfluidic Synthesis of Over One Thousand Uniquely Identifiable Spectral Codes

Encoded microparticles have become a powerful tool for a wide array of applications, including high-throughput sample tracking and massively parallel biological multiplexing. Spectral encoding, where particles are encoded with distinct luminescence spectra, provides a particularly appealing encoding strategy because of the ease of reading codes and assay flexibility. To date, spectral encoding has been limited in the number of codes that can be accurately resolved. Here, we demonstrate an automated 5-dimensional spectral encoding scheme using lanthanide nanophosphors that is capable of producing isotropic spherical microparticles with up to 1,100 unique codes, which we term MRBLEs (Microspheres with Ratiometric Barcode Lanthanide Encoding). We further develop a quantitative framework for evaluating global ability to distinguish codes and demonstrate that for six different sets of MRBLEs ranging from 106 to 1,101 codes in size, > 98% of MRBLEs can be assigned to a code with 99.99% confidence. These > 1,000 code sets represent the largest spectral code libraries built to date. We expect that these MRBLEs will enable a wide variety of novel multiplexed assays.

Broadband optical transparency in plasmonic nanocomposite polymer films via exciton-plasmon energy transfer

Inherent absorptive losses affect the performance of all plasmonic devices, limiting their fascinating applications in the visible range. Here, we report on the enhanced optical transparency obtained as a result of the broadband mitigation of optical losses in nanocomposite polymeric films, embedding core-shell quantum dots (CdSe@ZnS QDs) and gold nanoparticles (Au-NPs). Exciton-plasmon coupling enables non-radiative energy transfer processes from QDs to metal NPs, resulting in gain induced transparency of the hybrid flexible systems. Experimental evidences, such as fluorescence quenching and modifications of fluorescence lifetimes confirm the presence of this strong coupling between plexcitonic elements. Measures performed by means of an ultra-fast broadband pump-probe setup demonstrate loss compensation of gold NPs dispersed in plastic network in presence of gain. Furthermore, we compare two films containing different concentrations of gold NPs and same amount of QDs, to investigate the role of acceptor concentration (Au-NPs) in order to promote an effective and efficient energy transfer mechanism. Gain induced transparency in bulk systems represents a promising path towards the realization of loss compensated plasmonic devices.

Microfluidic generation of magnetic-fluorescent Janus microparticles for biomolecular detection

Fluorescent magnetic multifunctional microparticles were fabricated by a facile droplet microfluidic strategy. Two sodium alginate streams, one doped with Fe3O4 nanoparticles (NPs) and the other with CdSe/ZnS quantum dots, were introduced into a flow-focusing channel as a type of parallel laminar flow to form droplets containing two distinct parts. Then, at the serpentine channel, the Ca(2+) in the oil phase diffused into the droplets, causing the solidification of the droplets. Thus, the Janus microparticles with excellent magnetic/fluorescent properties formed. The flow conditions were optimized and the effects of the flow rates on magnetic/fluorescent compositions were carefully investigated. Luminescent labeling and magnetic separation were simultaneously realized with the newly designed microparticles. Moreover, spatial separation between Fe3O4 NPs and QDs prevented the interference of QDs photoluminescence by the magnetic particles. The as-prepared fluorescent magnetic Janus particles were also successfully employed for DNA assay, which demonstrated the potential of the multifunctional microbeads in biological applications.

Microfluidic synthesis of barcode particles for multiplex assays

The increasing use of high-throughput assays in biomedical applications, including drug discovery and clinical diagnostics, demands effective strategies for multiplexing. One promising strategy is the use of barcode particles that encode information about their specific compositions and enable simple identification. Various encoding mechanisms, including spectroscopic, graphical, electronic, and physical encoding, have been proposed for the provision of sufficient identification codes for the barcode particles. These particles are synthesized in various ways. Microfluidics is an effective approach that has created exciting avenues of scientific research in barcode particle synthesis. The resultant particles have found important application in the detection of multiple biological species as they have properties of high flexibility, fast reaction times, less reagent consumption, and good repeatability. In this paper, research progress in the microfluidic synthesis of barcode particles for multiplex assays is discussed. After introducing the general developing strategies of the barcode particles, the focus is on studies of microfluidics, including their design, fabrication, and application in the generation of barcode particles. Applications of the achieved barcode particles in multiplex assays will be described and emphasized. The prospects for future development of these barcode particles are also presented.

Microfluidic generation of multicolor quantum-dot-encoded core-shell microparticles with precise coding and enhanced stability

A novel microfluidic approach is developed to prepare multicolor QDs-encoded core-shell microparticles with precise and various barcode and enhanced stability performance. With the protection of the hydrogel shell, the leakage of QDs is avoided and the fluorescent stability is enhanced greatly. By embedding different QDs into different cores, no interaction between different QDs existed and the fluorescence spectrum of each kind of QDs can be recorded, respectively. Compared with QDs mixtures in a single particle, it is unnecessary to separate the emissions of QDs in different colors, and deconvolution algorithms are not needed. Therefore, it still maintains precise coding even if QDs with approximate emission wavelengths are used.

Plasmon mediated super-absorber flexible nanocomposites for metamaterials

A flexible host has been selected to achieve, for the first time, functional nanocomposites based on CdSe@ZnS core-shell type quantum dots (QDs) and Au nanoparticles (NPs), simultaneously dispersed in a polymer matrix. Coherent interactions between QDs and plasmonic Au NPs embedded in PDMS films have been demonstrated to lead to a relevant enhancement of the absorption cross-section of the QDs, remarkably modifying the optical response of the entire system. Optical and time resolved spectroscopy studies revealed an active gain-plasmon feedback behind the super-absorbing overall effect.

Dripping and jetting in microfluidic multiphase flows applied to particle and fiber synthesis

Dripping and jetting regimes in microfluidic multiphase flows have been investigated extensively, and this review summarizes the main observations and physical understandings in this field to date for three common device geometries: coaxial, flow-focusing and T-junction. The format of the presentation allows for simple and direct comparison of the different conditions for drop and jet formation, as well as the relative ease and utility of forming either drops or jets among the three geometries. The emphasis is on the use of drops and jets as templates for microparticle and microfiber syntheses, and a description is given of the more common methods of solidification and strategies for achieving complex multicomponent microparticles and microfibers.

Programmable microfluidic synthesis of spectrally encoded microspheres

Spectrally encoded fluorescent beads are an attractive platform for assay miniaturization and multiplexing in the biological sciences. Here, we synthesize hydrophilic PEG-acrylate polymer beads encoded with lanthanide nanophosphors using a fully automated microfluidic synthesis device. These beads are encoded by including varying amounts of two lanthanide nanophosphors relative to a third reference nanophosphor to generate 24 distinct ratios. These codes differ by less than 3% from their target values and can be distinguished from each other with an error rate of <0.1%. The encoded bead synthesis strategy we have used is readily extensible to larger numbers of codes, potentially up to millions, providing a new platform technology for assay multiplexing.