Polymer-based photocoupling agent for the efficient immobilization of nanomaterials and small molecules

Advancements in Nanomaterial Dispersion and Stability and Thermophysical Properties of Nano-Enhanced Phase Change Materials for Biomedical Applications

Phase change materials (PCMs) are materials that exhibit thermal response characteristics, allowing them to be utilized in the biological field for precise and controllable temperature regulation. Due to considerations of biosafety and the spatial limitations within human tissue, the amount of PCMs used in medical applications is relatively small. Therefore, researchers often augment PCMs with various materials to enhance their performance and increase their practical value. The dispersion of nanoparticles to modify the thermophysical properties of PCMs has emerged as a mature concept. This paper aims to elucidate the role of nanomaterials in addressing deficiencies and enhancing the performance of PCMs. Specifically, it discusses the dispersion methods and stabilization mechanisms of nanoparticles within PCMs, as well as their effects on thermophysical properties such as thermal conductivity, latent heat, and specific heat capacity. Furthermore, it explores how various nano-additives contribute to improved thermal conductivity and the mechanisms underlying enhanced latent heat and specific heat. Additionally, the potential applications of PCMs in biomedical fields are proposed. Finally, this paper provides a comprehensive analysis and offers suggestions for future research to maximize the utilization of nanomaterials in enhancing the thermophysical properties of PCMs for biomedical applications.

Trehalose-Grafted Glycopolymer: Synthesis via the Staudinger Reaction and Capture of Mycobacteria

A new trehalose-grafted poly(2-hydroxyethyl methacrylate) (HEMA) glycopolymer was synthesized via the perfluorophenyl azide (PFPA)-mediated Staudinger reaction between poly(HEMA-co-HEMA-PFPA) and a diphenylphosphine-derivatized trehalose. The reaction occurred rapidly at room temperature without the use of any catalyst, giving the trehalose glycopolymers over 68% yield after 1 h. The grafting density of trehalose can be controlled by the copolymer composition in poly(HEMA-co-HEMA-PFPA), resulting in 6.1% (TP1) or 37% (TP2) at 10:1 and 1:1 HEMA/HEMA-PFPA feed ratio, respectively. The trehalose glycopolymer was covalently attached on glass slides or silicon wafers using a thin film of poly(HEMA-co-HEMA-PFPA) as the adhesion layer, achieved through the C-H insertion reaction of the photogenerated singlet perfluorophenyl nitrene. To demonstrate the ability of the trehalose glycopolymer to capture mycobacteria, arrays of the trehalose glycopolymer were fabricated and treated with Mycobacterium smegmatis. Results from the optical, fluorescence, and scanning electron microscopy showed that mycobacteria were indeed captured on the trehalose glycopolymer. The amount of mycobacteria captured increased with the percent trehalose in the trehalose glycopolymer and also with the concentration of the trehalose glycopolymer. In addition, the captured bacteria could be visualized by the naked eye under the illumination of a hand-held UV lamp.

Surface-Immobilized Photoinitiators for Light Induced Polymerization and Coupling Reactions

Straightforward and versatile surface modification, functionalization and coating have become a significant topic in material sciences. While physical modification suffers from severe drawbacks, such as insufficient stability, chemical induced grafting processes efficiently modify organic and inorganic materials and surfaces due to covalent linkage. These processes include the "grafting from" method, where polymer chains are directly grown from the surface in terms of a surface-initiated polymerization and the "grafting to" method where a preformed (macro)-molecule is introduced to a preliminary treated surface via a coupling reaction. Both methods require an initiating species that is immobilized at the surface and can be triggered either by heat or light, whereas light induced processes have recently received increasing interest. Therefore, a major challenge is the ongoing search for suitable anchor moieties that provide covalent linkage to the surface and include initiators for surface-initiated polymerization and coupling reactions, respectively. This review containing 205 references provides an overview on photoinitiators which are covalently coupled to different surfaces, and are utilized for subsequent photopolymerizations and photocoupling reactions. An emphasis is placed on the coupling strategies for different surfaces, including oxides, metals, and cellulosic materials, with a focus on surface coupled free radical photoinitiators (type I and type II). Furthermore, the concept of surface initiation mediated by photoiniferters (PIMP) is reviewed. Regarding controlled radical polymerization from surfaces, a large section of the paper reviews surface-tethered co-initiators, ATRP initiators, and RAFT agents. In combination with photoinitiators or photoredox catalysts, these compounds are employed for surface initiated photopolymerizations. Moreover, examples for coupled photoacids and photoacid generators are presented. Another large section of the article reviews photocoupling and photoclick techniques. Here, the focus is set on light sensitive groups, such as organic azides, tetrazoles and diazirines, which have proven useful in biochemistry, composite technology and many other fields.

On the Reactivity Enhancement of Graphene by Metallic Substrates towards Aryl Nitrene Cycloadditions

Pristine graphene is fairly inert chemically, and as such, most application-driven studies use graphene oxide, or reduced graphene oxide. Using substrates to modulate the reactivity of graphene represents a unique strategy in the covalent functionalization of this otherwise fairly inert material. It was found that the reactivity of pristine graphene towards perfluorophenyl azide (PFPA) can be enhanced by a metal substrate on which graphene is supported. Results on the extent of functionalization, defect density, and reaction kinetics all show that graphene supported on Ni (G/Ni) has the highest reactivity toward PFPA, followed by G/Cu and then G/silicon wafer. DFT calculations suggest that the metal substrate stabilizes the physisorbed nitrene through enhanced electron transfer to the singlet nitrene from the graphene surface assisted by the electron rich metal substrate. The G/Ni substantially stabilizes the singlet nitrene relative to G/Cu and the free-standing graphene. The product structure is also predicted to be substrate dependent. These findings open up opportunities to enhance the reactivity of pristine graphene simply through the selection of the substrate. This also represents a new and powerful approach to increasing the reactivity of singlet nitrenes through direct electronic communication with graphene.

Reducing Friction in the Eye: A Comparative Study of Lubrication by Surface-Anchored Synthetic and Natural Ocular Mucin Analogues

Biomaterials used in the ocular environment should exhibit specific tribological behavior to avoid discomfort and stress-induced epithelial damage during blinking. In this study, two macromolecules that are commonly employed as ocular biomaterials, namely, poly(vinylpyrrolidone) (PVP) and hyaluronan (HA), are compared with two known model glycoproteins, namely bovine submaxillary mucin (BSM) and α₁-acid glycoprotein (AGP), with regard to their nonfouling efficiency, wettability, and tribological properties when freely present in the lubricant, enabling spontaneous adsorption, and when chemisorbed under low contact pressures. Chemisorbed coatings were prepared by means of photochemically triggered nitrene insertion reactions. BSM and AGP provided boundary lubrication when spontaneously adsorbed in a hydrophobic contact with a coefficient of friction (CoF) of ∼0.03-0.04. PVP and HA were found to be excellent boundary lubricants when chemisorbed (CoF ≤ 0.01). Notably, high-molecular-weight PVP generated thick adlayers, typically around 14 nm, and was able to reduce the CoF below 0.005 when slid against a BSM-coated poly(dimethylsiloxane) pin in a tearlike fluid.

Poly(HEMA-co-HEMA-PFPA): Synthesis and preparation of stable micelles encapsulating imaging nanoparticles

We report the preparation of stable micelles from random copolymers of 2-hydroxyethyl methacrylate (HEMA) and perfluorophenyl azide (PFPA)-derivatized HEMA (HEMA-PFPA). The copolymers were synthesized by RAFT polymerization at room temperature under mild conditions without affecting the azide functionality. Upon addition of water to the copolymer solution in DMSO, the random copolymers self-assembled into micelles even at the percentage of HEMA-PFPA as low as 4.5%. The size of the micelles can be controlled by the molecular weight and the concentration of the copolymer, and the percentage of HEMA-PFPA in the copolymer. In addition, iron oxide nanoparticles and quantum dots were successfully encapsulated into the micelles with high encapsulation efficiency (∼80%). These nanoparticles, which were hydrophobic and formed agglomerates in water, became fully dispersed after encapsulating into the micelles. The micelles were stable and the size remained unchanged for at least 6months.

Three-Dimensional Graphene-TiO2 Nanocomposite Photocatalyst Synthesized by Covalent Attachment

We report the synthesis of a three-dimensional graphene (3DG)-TiO2 nanocomposite by covalently attaching P25 TiO2 nanoparticles onto pristine 3DG through a perfluorophenyl azide-mediated coupling reaction. The TiO2 nanoparticles were robustly attached on the 3DG surface, with minimal particle agglomeration. In photocatalytic CO2 reduction, the 3DG-TiO2 nanocomposite demonstrated excellent activity, about 11 times higher than that of the P25 TiO2 nanoparticles. The enhanced activity can be partially attributed to the highly dispersed state of the P25 TiO2 nanoparticles on the 3DG substrate. This 3DG-based system offers a new platform for fabricating photocatalytic materials with enhanced activities.

Fabrication of carbohydrate microarrays on a poly(2-hydroxyethyl methacrylate)-based photoactive substrate

A carbohydrate microarray was fabricated on a PHEMA-based photoactive polymer. The arrays showed strong signals, and were used to probe carbohydrate-mediated interactions with lectin and bacteria.

Ionization of covalent immobilized poly(4-vinylphenol) monolayers measured by ellipsometry, QCM and SPR

Covalently immobilized poly(4-vinylphenol) (PVP) monolayer films were fabricated by spin coating PVP on perfluorophenyl azide (PFPA)-functionalized surface followed by UV irradiation. The pH-responsive behavior of these PVP ultrathin films was evaluated by ellipsometry, quartz crystal microbalance (QCM) and surface plasmon resonance (SPR). By monitoring the responses of these films to pH in situ, the ionization constant of the monolayer thin films was obtained. The apparent pKa value of these covalently immobilized PVP monolayers, 13.4 by SPR, was 3 units higher than that of the free polymer in aqueous solution.

Anilide formation from thioacids and perfluoroaryl azides

A metal-free method for fast and clean anilide formation from perfluoroaryl azide and thioacid is presented. The reaction proved highly efficient, displaying fast kinetics, high yield, and good chemoselectivity. The transformation was compatible with various solvents and tolerant to a wide variety of functional groups, and it showed high performance in polar protic/aprotic media, including aqueous buffer systems.

Photoconjugation of molecularly imprinted polymer with magnetic nanoparticles

Because of their synthetic accessibility, molecularly imprinted polymer (MIP) nanoparticles are ideal building blocks for preparing multifunctional composites. In this work, we developed a general photocoupling chemistry to enable simple conjugation of MIP nanoparticles with inorganic magnetic nanoparticles. We first synthesized MIP nanoparticles using propranolol as a model template and perfluorophenyl azide-modified silica-coated magnetic nanoparticles. Using a simple photoactivation followed by facile purification with a magnet, we obtained magnetic composite particles that showed selective uptake of propranolol. We characterized the nanoparticles and composite materials using FT-IR, TEM, fluorescence spectroscopy, and radioligand binding analysis. Through the high molecular selectivity of the magnetic composite, we demonstrated the nondestructive feature and the high efficiency of the photocoupling chemistry. The versatile photoconjugation method developed in this work should also be very useful for combining organic MIPs with other inorganic nanoparticles to enable new chemical sensors and high efficiency photocatalysts.

Sensitive detection of food-borne pathogen Salmonella by modified PAN fibers-immunoassay

Sensitive and rapid detection of Salmonella is a key to the prevention and identification of problems associated with human health and safety. Enzyme Linked Immunosorbent Assays (ELISAs) are popular and widely implemented technique to detect pathogenic bacteria in routine analysis but a typical ELISA yields a sensitivity of 10(6)-10(7)cfu/mL. The present study consecrates on the applicability of surface modified polyacrylonitrile (PAN) fibers as a novel matrix of immunoassay for the detection of Salmonella typhimurium in a sandwich ELISA format. Affinity purified antibody against Salmonella common structural antigen (CSA-1-Ab) was immobilized on modified PAN (mPAN) fibers using covalent immobilization via amine-glutaraldehyde chemistry and inactivated S. typhimurium were captured from various samples and detected colorimetrically using peroxidase-labelled common structural antibody (CSA-1-Ab-HRP) against Salmonella. The performance of the developed immunoassay was compared with commercially available immunomagnetic microbeads (Dynabeads(®) anti-Salmonella), polystyrene (PS) microtitre plate and glutaraldehyde activated PS plate. Limit of detection (LOD) was found to be 10, 10(5), 10(6) and 10(7)cells/mL of bacteria for mPAN, Dynabeads(®), glu-plate and PS plate respectively without any pre-enrichment step. The assay was specific for the targeted bacteria when investigated with other cross-reactant food and water-borne pathogens. The developed immunoassay offered undisputed advantages of being simple, sensitive and specific for the detection of S. typhimurium.

Covalent functionalization of graphene with reactive intermediates

Graphene, a material made exclusively of sp(2) carbon atoms with its π electrons delocalized over the entire 2D network, is somewhat chemically inert. Covalent functionalization can enhance graphene's properties including opening its band gap, tuning conductivity, and improving solubility and stability. Covalent functionalization of pristine graphene typically requires reactive species that can form covalent adducts with the sp(2) carbon structures in graphene. In this Account, we describe graphene functionalization reactions using reactive intermediates of radicals, nitrenes, carbenes, and arynes. These reactive species covalently modify graphene through free radical addition, CH insertion, or cycloaddition reactions. Free radical additions are among the most common reaction, and these radicals can be generated from diazonium salts and benzoyl peroxide. Electron transfer from graphene to aryl diazonium ion or photoactivation of benzoyl peroxide yields aryl radicals that subsequently add to graphene to form covalent adducts. Nitrenes, electron-deficient species generated by thermal or photochemical activation of organic azides, can functionalize graphene very efficiently. Because perfluorophenyl nitrenes show enhanced bimolecular reactions compared with alkyl or phenyl nitrenes, perfluorophenyl azides are especially effective. Carbenes are used less frequently than nitrenes, but they undergo CH insertion and C═C cycloaddition reactions with graphene. In addition, arynes can serve as a dienophile in a Diels-Alder type reaction with graphene. Further study is needed to understand and exploit the chemistry of graphene. The generation of highly reactive intermediates in these reactions leads to side products that complicate the product composition and analysis. Fundamental questions remain about the reactivity and regioselectivity of graphene. The differences in the basal plane and the undercoordinated edges of graphene and the zigzag versus arm-chair configurations warrant comprehensive studies. The availability of well-defined pristine graphene starting materials in large quantities remains a key obstacle to the advancement of synthetic graphene chemistry.

Antifouling surfaces for proteins labeled with dye-doped silica nanoparticles

We report that proteins labeled with fluorescein-doped silica nanoparticles (FSNPs) showed drastically different fouling behavior than those labeled with the fluorescein dye. Arrays of polymer films were covalently immobilized on silicon wafers and were treated with protein conjugated on FSNPs. Fluorescence imaging showed that the protein-FSNP conjugate adsorbed strongly on hydrophilic polymers such as poly(ethylene oxide) (PEO) and weakly on hydrophobic polymers such as polystyrene (PS), and the extent of adsorption decreased with increasing hydrophobicity of the polymer film. Thus, carbohydrate microarrays probed with FSNP-labeled lectin showed significantly enhanced signals when PS was used as the antifouling coating than when PEO was used, or when using bovine serum albumin as the blocking agent.

Photoreactive azido-containing silica nanoparticle/polycation multilayers: durable superhydrophobic coating on cotton fabrics

In this study, we report the functionalization of silica nanoparticles with highly photoreactive phenyl azido groups and their utility as a negatively charged building block for layer-by-layer (LbL) electrostatic assembly to produce a stable silica nanoparticle coating. Azido-terminated silica nanoparticles were prepared by the functionalization of bare silica nanoparticles with 3-aminopropyltrimethoxysilane followed by the reaction with 4-azidobenzoic acid. The azido functionalization was confirmed by FTIR and XPS. Poly(allylamine hydrochloride) was also grafted with phenyl azido groups and used as photoreactive polycations for LbL assembly. For the photoreactive silica nanoparticle/polycation multilayers, UV irradiation can induce the covalent cross-linking within the multilayers as well as the anchoring of the multilayer film onto the organic substrate, through azido photochemical reactions including C-H insertion/abstraction reactions with surrounding molecules and dimerization of azido groups. Our results show that the stability of the silica nanoparticle/polycation multilayer film was greatly improved after UV irradiation. Combined with a fluoroalkylsilane post-treatment, the photoreactive LbL multilayers were used as a coating for superhydrophobic modification of cotton fabrics. Herein the LbL assembly method enables us to tailor the number of the coated silica nanoparticles through the assembly cycles. The superhydrophobicity of cotton fabrics was durable against acids, bases, and organic solvents, as well as repeated machine wash. Because of the unique azido photochemistry, the approach used here to anchor silica nanoparticles is applicable to almost any organic substrate.

Fabrication of glyconanoparticle microarrays

We report a new type of microarray, based on glyconanoparticles (GNPs), to study glycan-lectin interactions. GNPs, synthesized by conjugating carbohydrate ligands on silica nanoparticles, were printed on a photoactive surface followed by covalent immobilization by light activation. The GNP microarrays could be probed by lectins labeled with fluorescein as well as fluorescein-doped silica nanoparticles (FSNPs). Results showed that FSNP as the label enhanced the signals for the higher affinity ligands than the lower ones.

Evaluation of photochemically immobilized poly(2-ethyl-2-oxazoline) thin films as protein-resistant surfaces

Poly(2-ethyl-2-oxazoline) (PEOX) of various molecular weights were covalently immobilized on silicon wafers and gold slides to form protein-resistant surfaces via a fast and general photocoupling chemistry based on the CH insertion reaction of light-activated perfluorophenyl azide (PFPA). The thicknesses of the immobilized PEOX films ranged from 23 to 80 Å for molecular weight of 5000 to 500,000, and the grafting density reached 3.2 × 10(-3) Å(-2) for PEOX 5000. The protein-resistant property of the films was studied using bovine serum albumin (BSA) by fluorescence imaging, ellipsometry, and surface plasmon resonance imaging (SPRi). The fluorescence imaging and ellipsometry studies showed the largest amount of BSA adsorbed on PEOX 5000 and the smallest on PEOX 500,000. This was consistent with the kinetic analysis of BSA adsorption by SPRi showing that PEOX 5000 exhibited the fastest association rate and the slowest dissociation rate whereas PEOX 500,000 had the slowest association rate and the fastest dissociation rate. The PEOX film was then applied in the fabrication of carbohydrate microarrays to reduce the nonspecific adsorption of lectins and thus the background noises. Results showed that the microarray signals were significantly enhanced when the PEOX film was used.