Hydrogel-Based Glucose Sensors: Effects of Phenylboronic Acid Chemical Structure on Response

Phenylboronic acids (PBAs) are being considered for glucose sensing and controlled insulin release, because of their affinity for diol-containing molecules. The interaction of immobilized PBAs in a hydrogel matrix with glucose can lead to volumetric changes that have been used to monitor glucose concentration and release insulin. Although the interaction of PBAs with diol-containing molecules has been intensively studied, the response of PBA-modified hydrogels as a function of the specific PBA chemistry is not well understood. To understand the interaction of immobilized PBAs with glucose in hydrogel systems under physiological conditions, the glucose-dependent volumetric changes of a series of hydrogel sensors functionalized with different classes of PBAs were investigated. The volume change induced by PBA-glucose interactions is converted to the diffracted wavelength shift by a crystalline colloidal array embedded in the hydrogel matrix. The PBAs studied contain varying structural parameters such as the position of the boronic acid on the phenyl ring, different substituents on PBAs and different linkers to the hydrogel backbone. The volumetric change of the PBA modified hydrogels is found to be highly dependent on the chemical structure of the immobilized PBAs. The PBAs that appear to provide linear volumetric responses to glucose are found to also have slow response kinetics and significant hysteresis, while PBAs that show nonlinear responses have fast response kinetics and small hysteresis. Electron-withdrawing substituents, which reduce the p<i>K</i>_a of PBAs, either increase or decrease the magnitude of response, depending on the exact chemical structure. The response rate is increased by PBAs with electron-withdrawing substituents. Addition of a methylene bridge between the PBA and hydrogel backbone leads to a significant decrease in the response magnitude. PBAs with specific desirable features can be selected from the pool of available PBAs and other PBA derivatives with desired properties can be designed according to the findings reported here

Aqueous Zinc Compounds as Residual Antimicrobial Agents for Textiles

Textiles, especially those worn by patients and medical professionals, serve as vectors for proliferating pathogens. Upstream manufacturing techniques and end-user practices, such as transition-metal embedment in textile fibers or alcohol-based disinfectants, can mitigate pathogen growth, but both techniques have their shortcomings. Fiber embedment requires complete replacement of all fabrics in a facility, and the effects of embedded nanoparticles on human health remain unknown. Alcohol-based, end-user disinfectants are short-lived because they quickly volatilize. In this work, common zinc salts are explored as an end-user residual antimicrobial agent. Zinc salts show cost-effective and long-lasting antimicrobial efficacy when solution-deposited on common textiles, such as nylon, polyester, and cotton. Unlike common alcohol-based disinfectants, these zinc salt-treated textiles mitigate microbial growth for more than 30 days and withstand commercial drying. Polyester fabrics treated with ZnO and ZnCl₂ were further explored because of their commercial ubiquity and likelihood for rapid commercialization. ZnCl₂-treated textiles were found to retain their antimicrobial coating through abrasive testing, whereas ZnO-treated textiles did not. Scanning electron microscopy, Fourier transform infrared spectroscopy, and differential scanning calorimetry analyses suggest that ZnCl₂ likely hydrolyzes and reacts with portions of the polyester fiber, chemically attaching to the fiber, whereas colloidal ZnO simply sediments and binds with weaker physical interactions

Dealkylation of Poly(methyl methacrylate) by TiCl₄ Vapor Phase Infiltration (VPI) and the Resulting Chemical and Thermophysical Properties of the Hybrid Material

This study examines the chemical reaction pathways for vapor phase infiltration (VPI) of TiCl4 into poly(methyl methacrylate) (PMMA). VPI is a processing method that transforms organic polymers into organic–inorganic hybrid materials with new properties of interest for microelectronic patterning, technical textiles, and chemical separations. Understanding the fundamental chemical mechanisms of the VPI process is essential for establishing approaches to design the chemical structure and properties of these hybrid materials. While prior work has suggested that TiCl4 infiltration into PMMA does not disrupt the polymer’s carbonyl bond, a clear reaction mechanism has yet to be proposed. Here, we present a detailed X-ray photoelectron spectroscopy study that presents evidence for a concerted reaction mechanism that involves TiCl4 coordinating with the PMMA’s ester group to dealkylate the methyl side group, creating a chloromethane byproduct and primary chemical bonds between the organic and inorganic components of the hybrid material. Additional spectroscopy, quartz crystal microbalance gravimetry, and thermophysical and chemical property measurements of this material, including solubility studies and thermal expansion measurements, provide further evidence for this chemical reaction pathway and the subsequent creation of inorganic cross-links that network these TiOx–PMMA hybrid materials

Informatics-Driven Design of Superhard B–C–O Compounds

Materials containing B, C, and O, due to the advantages of forming strong covalent bonds, may lead to materials that are superhard, i.e., those with a Vicker’s hardness larger than 40 GPa. However, the exploration of this vast chemical, compositional, and configurational space is nontrivial. Here, we leverage a combination of machine learning (ML) and first-principles calculations to enable and accelerate such a targeted search. The ML models first screen for potentially superhard B–C–O compositions from a large hypothetical B–C–O candidate space. Atomic-level structure search using density functional theory (DFT) within those identified compositions, followed by further detailed analyses, unravels on four potentially superhard B–C–O phases exhibiting thermodynamic, mechanical, and dynamic stability

Stabilizing Small Molecules on Metal Oxide Surfaces Using Atomic Layer Deposition

Device lifetimes and commercial viability of dye-sensitized solar cells (DSSCs) and dye-sensitized photoelectrosynthesis cells (DSPECs) are dependent on the stability of the surface bound molecular chromophores and catalysts. Maintaining the integrity of the solution-metal oxide interface is especially challenging in DSPECs for water oxidation where it is necessary to perform high numbers of turnovers, under irradiation in an aqueous environment. In this study, we describe the atomic layer deposition (ALD) of TiO₂ on nanocrystalline TiO₂ prefunctionalized with the dye molecule [Ru­(bpy)₂(4,4′-(PO₃H₂)­bpy)]²⁺ (RuP) as a strategy to stabilize surface bound molecules. The resulting films are over an order of magnitude more photostable than untreated films and the desorption rate constant exponentially decreases with increased thickness of ALD TiO₂ overlayers. However, the injection yield for TiO₂-RuP with ALD TiO₂ also decreases with increasing overlayer thickness. The combination of decreased injection yield and 95% quenched emission suggests that the ALD TiO₂ overlayer acts as a competitive electron acceptor from RuP*, effectively nonproductively quenching the excited state. The ALD TiO₂ also increases back electron transfer rates, relative to the untreated film, but is independent of overlayer thickness. The results for TiO₂-RuP with an ALD TiO₂ overlayer are compared with similar films having ALD Al₂O₃ overlayers

Highly Conductive and Conformal Poly(3,4-ethylenedioxythiophene) (PEDOT) Thin Films via Oxidative Molecular Layer Deposition

This work introduces oxidative molecular layer deposition (oMLD) as a chemical route to synthesize highly conductive and conformal poly­(3,4-ethylenedioxythiophene) (PEDOT) thin films via sequential vapor exposures of molybdenum­(V) chloride (MoCl₅, oxidant) and ethylene dioxythiophene (EDOT, monomer) precursors. The growth temperature strongly affects PEDOT’s crystalline structure and electronic conductivity. Films deposited at ∼150 °C exhibit a highly textured crystalline structure, with {010} planes aligned parallel with the substrate. Electrical conductivity of these textured films is routinely above 1000 S cm^–1, with the most conductive films exceeding 3000 S cm^–1. At lower temperatures (∼100 °C) the films exhibit a random polycrystalline structure and display smaller conductivities. Compared with typical electrochemical, solution-based, and chemical vapor deposition techniques, oMLD PEDOT films achieve high conductivity without the need for additives or postdeposition treatments. Moreover, the sequential-reaction synthesis method produces highly conformal coatings over high aspect ratio structures, making it attractive for many device applications

Atomic Layer Deposition of TiO₂ on Mesoporous nanoITO: Conductive Core–Shell Photoanodes for Dye-Sensitized Solar Cells

Core–shell structures consisting of thin shells of conformal TiO₂ deposited on high surface area, conductive Sn-doped In₂O₃ nanoparticle. Mesoscopic films were synthesized by atomic layer deposition and studied for application in dye-sensitized solar cells. Results obtained with the N719 dye show that short-circuit current densities, open-circuit voltages, and back electron transfer lifetimes all increased with increasing TiO₂ shell thickness up to 1.8–2.4 nm and then decline as the thickness was increased further. At higher shell thicknesses, back electron transfer to −Ru^III is increasingly competitive with transport to the nanoITO core resulting in decreased device efficiencies

Effect of Meso- and Micro-Porosity in Carbon Electrodes on Atomic Layer Deposition of Pseudocapacitive V₂O₅ for High Performance Supercapacitors

Atomic layer deposition (ALD) of vanadium oxide is a viable means to add pseudocapacitive layers to porous carbon electrodes. Two commercial activated carbon materials with different surface areas and pore structures were acid treated and coated by V₂O₅ ALD using vanadium triisopropoxide and water at 150 °C. The V₂O₅ ALD process was characterized at various temperatures to confirm saturated ALD growth conditions. Capacitance and electrochemical impedance analysis of subsequently constructed electrochemical capacitors (ECs) showed improved charge storage for the ALD coated electrodes, but the extent of improvement depended on initial pore structure. The ALD of V₂O₅ onto mesoporous carbon increased the capacitance by up to 46% after 75 ALD cycles and obtained a maximum pseudocapacitance of 540 F/g­(V₂O₅) after 25 ALD cycles, while maintaining low electrical resistance, high columbic efficiency, and a high cycle life. However, adding V₂O₅ ALD to microporous carbons with pore diameters of <11 Å showed far less improvement, likely due to “blocking off” of the micropores and reducing the accessible surface area. Results show that ALD is a viable means to construct high-performance supercapacitors from activated carbon which is the basis for commercial products, and a clear understanding of carbon electrode pore structure, layer conformality, and layer thickness are necessary to fully optimize performance

Facile Conversion of Hydroxy Double Salts to Metal–Organic Frameworks Using Metal Oxide Particles and Atomic Layer Deposition Thin-Film Templates

Rapid room-temperature synthesis of metal–organic frameworks (MOFs) is highly desired for industrial implementation and commercialization. Here we find that a (Zn,Cu) hydroxy double salt (HDS) intermediate formed <i>in situ</i> from ZnO particles or thin films enables rapid growth (<1 min) of HKUST-1 (Cu₃(BTC)₂) at room temperature. The space-time-yield reaches >3 × 10⁴ kg·m^–3·d^–1, at least 1 order of magnitude greater than any prior report. The high anion exchange rate of (Zn,Cu) hydroxy nitrate HDS drives the ultrafast MOF formation. Similarly, we obtained Cu-BDC, ZIF-8, and IRMOF-3 structures from HDSs, demonstrating synthetic generality. Using ZnO thin films deposited via atomic layer deposition, MOF patterns are obtained on pre-patterned surfaces, and dense HKUST-1 coatings are grown onto various form factors, including polymer spheres, silicon wafers, and fibers. Breakthrough tests show that the MOF-functionalized fibers have high adsorption capacity for toxic gases. This rapid synthesis route is also promising for new MOF-based composite materials and applications

Stabilization of Polyoxometalate Water Oxidation Catalysts on Hematite by Atomic Layer Deposition

Fast and earth-abundant-element polyoxometalates (POMs) have been heavily studied recently as water oxidation catalysts (WOCs) in homogeneous solution. However, POM WOCs can be quite unstable when supported on electrode or photoelectrode surfaces under applied potential. This article reports for the first time that a nanoscale oxide coating (Al₂O₃) applied by the atomic layer deposition (ALD) aids immobilization and greatly stabilizes this now large family of molecular WOCs when on electrode surfaces. In this study, [{Ru^IV₄(OH)₂(H₂O)₄}­(γ-SiW₁₀O₃₄)₂]^10– (<b>Ru</b>_<b>4</b><b>Si</b>_<b>2</b>) is supported on hematite photoelectrodes and then protected by ALD Al₂O₃; this ternary system was characterized before and after photoelectrocatalytic water oxidation by Fourier transform infrared, X-ray photoelectron spectroscopy, energy-dispersive X-ray, and voltammetry. All these studies indicate that <b>Ru</b>_<b>4</b><b>Si</b>_<b>2</b> remains intact with Al₂O₃ ALD protection, but not without. The thickness of the Al₂O₃ layer significantly affects the catalytic performance of the system: a 4 nm thick Al₂O₃ layer provides optimal performance with nearly 100% faradaic efficiency for oxygen generation under visible-light illumination. Al₂O₃ layers thicker than 6.5 nm appear to completely bury the <b>Ru</b>_<b>4</b><b>Si</b>_<b>2</b> catalyst, removing all of the catalytic activity, whereas thinner layers are insufficient to maintain a long-term attachment of the catalytic POM