Photonic-Plasmonic Coupling Enhanced Fluorescence Enabling Digital-Resolution Ultrasensitive Protein Detection

Assays utilizing fluorophores are common throughout life science research and diagnostics, although detection limits are generally limited by weak emission intensity, thus requiring many labeled target molecules to combine their output to achieve higher signal-to-noise. We describe how the synergistic coupling of plasmonic and photonic modes can significantly boost the emission from fluorophores. By optimally matching the resonant modes of a plasmonic fluor (PF) nanoparticle and a photonic crystal (PC) with the absorption and emission spectrum of the fluorescent dye, a 52-fold improvement in signal intensity is observed, enabling individual PFs to be observed and digitally counted, where one PF tag represents one detected target molecule. The amplification can be attributed to the strong near-field enhancement due to the cavity-induced activation of the PF, PC band structure-mediated improvement in collection efficiency, and increased rate of spontaneous emission. The applicability of the method by dose-response characterization of a sandwich immunoassay for human interleukin-6, a biomarker used to assist diagnosis of cancer, inflammation, sepsis, and autoimmune disease is demonstrated. A limit of detection of 10 fg mL⁻¹ and 100 fg mL⁻¹ in buffer and human plasma respectively, is achieved, representing a capability nearly three orders of magnitude lower than standard immunoassays.     

Capillary-Scale Hydrogel Microchannel Networks by Wire Templating

Microvascular networks are essential for the efficient transport of nutrients, waste products, and drugs throughout the body. Wire-templating is an accessible method for generating laboratory models of these blood vessel networks, but it has difficulty fabricating microchannels with diameters of ten microns and narrower, a requirement for modeling human capillaries. This study describes a suite of surface modification techniques to  selectively control the interactions amongst wires, hydrogels, and world-to-chip interfaces. This wire templating method enables the fabrication of perfusable hydrogel-based rounded cross-section capillary-scale networks whose diameters controllably narrow at bifurcations down to 6.1 ± 0.3 microns in diameter. Due to its low cost, accessibility, and compatibility with a wide range of common hydrogels of tunable stiffnesses such as collagen, this technique may increase the fidelity of experimental models of capillary networks for the study of human health and disease.     

Methacrylic acid-based amphiphilic block-random copolymer stabilizers for emulsion polymerization

The emulsion polymerization of styrene was investigated using polystyrene-b-[polystyrene-r-poly(methacrylic acid)] amphiphilic block-random copolymers (BRCs) of different compositions as stabilizers. These stabilizers with molar masses <20,000 g/mol, which possess unique dispersion behaviour (i.e., self-assembly with low aggregation numbers) when dissolved in aqueous medium at alkaline pH, were prepared by the nitroxide-mediated bulk polymerization of styrene to achieve a desired molar mass followed by chain extension by batchwise addition of styrene and methacrylic acid monomers to obtain the stabilizing group. Emulsion polymerizations of styrene stabilized by these BRCs yielded stable latexes with particle diameters that range between 30 and 150 nm. When different concentrations of the stabilizer (2–3.5 mM) were utilized for emulsion polymerization of styrene, a similar novel emulsion polymerization mechanism observed previously by our group for the acrylic-acid based amphiphilic BRCs was also seen, further validating the difference between this class of polymeric surfactants and conventional small molecule surfactants, block copolymers, or alkali soluble resins. The performance of methacrylic-acid based BRCs was more efficient and yielded higher surface coverage of the polystyrene latexes when compared to the acrylic-acid based BRCs as a result of the more hydrophobic nature of the former.     

Rigid Polyurethane Foam Prepared from Extruded Starch-Derived Glycol Glucosides as Chemical Intermediates

Starch-derived glycol glucosides were prepared by a continuous, twin-screw extrusion process; reacted with propylene oxide; and evaluated as the polyether polyol (PP) in rigid polyurethane (RPU) foam. Cornstarch with 10% moisture, ethylene glycol (EG), and sulfuric acid as the catalyst were reacted at 160°C in the extruder, using 4 moles EG/mole starch anhydroglucose unit (AGU). After removing unreacted EG from the extrudate by vacuum distillation, the crude mixture of products, which contained at least 85% anomeric glucosides, was reacted with propylene oxide to form the PP with a hydroxyl number of 470. The PP was then deionized and reacted with a polymeric diisocyanate, using a conventional type of formulation and pour-in-place procedure. The same formulation and procedure were used to prepare RPU foam from a commercial methyl glucoside PP (hydroxyl number 443) for comparison. The insulating capacity, compressive strength, and dimensional stability properties of the foam with the experimental PP were at least as good as the foam with the commercial PP. This study demonstrates, for the first time, that the starch-derived glycol glucosides prepared by reactive extrusion processing are suitable chemical intermediates for the preparation of RPU foams with good properties. Also the study suggests that other types of starch-derived glucosides could be prepared by reactive extrusion processing for potential uses in foams, alkyd resins, surfactants and other products.