Display of Amino Groups on Substrate Surfaces by Simple Dip-Coating of Methacrylate-Based Polymers and Its Application to DNA Immobilization

The implementation of a reactive functional group onto a material surface is of great importance. Reactive functional groups (e.g., an amino group and a hydroxyl group) are usually hydrophilic, which makes it difficult to display them on a dry polymer surface. We here propose a novel method for displaying amino groups on the surfaces of polymeric substrates through dip-coating of a methacrylate-based copolymer. We synthesized copolymers composed of methyl methacrylate and 2-aminoethyl methacrylate with different protecting groups or ion-complexes on their amino groups, then dip-coated the copolymers onto a poly­(methyl methacrylate) (PMMA) substrate. Evaluation using a cleavable fluorescent compound, which was synthesized in the present study to quantify a small amount (pmol/cm²) of amino groups on a solid surface, revealed that the protection of amino groups affected their surface segregation in the copolymer coating. <i>p</i>-Toluenesulfonate ion-complex and <i>tert</i>-butoxycarbonyl (Boc) protection of amino groups were found to effectively display amino groups on the surface (more than 70 pmol/cm²). The density of amino groups displayed on a surface can be easily controlled by mixing the copolymer and PMMA before dip-coating. Dip-coating of the copolymer with Boc protection on various polymeric substrates also successfully displayed amino groups on their surfaces. Finally, we demonstrated that the amino groups displayed can be utilized for the immobilization of a DNA oligonucleotide on a substrate surface

Controlling Surface Segregation of a Polymer To Display Carboxy Groups on an Outermost Surface Using Perfluoroacyl Groups

Controlling the surface properties of solid polymers is important for practical applications. We here succeeded in controlling the surface segregation of polymers to display carboxy groups on an outermost surface, which allowed the covalent immobilization of functional molecules via the carboxy groups on a substrate surface. Random methacrylate-based copolymers containing carboxy groups, which were protected with perfluoroacyl (R_f) groups, were dip-coated on acrylic substrate surfaces. X-ray photoelectron spectroscopy and contact-angle measurements revealed that the R_f groups were segregated to the outermost surface of the dip-coated substrates. The R_f groups were removed by hydrolysis of the R_f esters in the copolymers, resulting in the display of carboxy groups on the surface. The quantification of carboxy groups on a surface revealed that the carboxy groups were reactive to a water-soluble solute in an aqueous solution. The surface segregation was affected by the molecular structure of the copolymer used for dip-coating

Conductive Gold Thin Film Prepared by the Two-Dimensional Assembly of Gold Nanoparticles on a Plastic Surface

Gold thin films are useful as conductive materials for electrical devices and sensors, owing to their high conductivity and inertness. In the present study, we propose a novel alternative to conventional gold-coating techniques (i.e., gold-vapor deposition and gold plating) to prepare a gold thin film on a plastic surface using a gold colloidal solution. Gold nanoparticles (AuNPs) were immobilized on a plastic surface with a high density of amino groups (two-dimensional assembly of AuNPs) and subsequently grew to form a gold thin film. The growth of the AuNPs was induced using an amino acid as the reducing agent. The selection of the amino acid significantly influenced the growth of the AuNPs and the morphology of the gold thin film. Microscopic observations and absorbance measurements demonstrated the growth and connection of the AuNPs on the surface. The thickness of the gold thin film was limited to between 50 nm and 0.5 μm by varying the growth conditions. The formed film was lustrous and exhibited electrical conductivity comparable to that of a gold-vapor deposited surface. Moreover, we successfully micropatterned the gold thin film on the plastic substrate using the present method combined with a microcontact printing method. The results indicate that our approach has significant potential for use in the manufacture of electrical devices and biosensors

Short Oligopeptides for Biocompatible and Biodegradable Supramolecular Hydrogels

Short Phe-rich oligopeptides, consisting of only four and five amino acids, worked as effective supramolecular hydrogelators for buffer solutions at low gelator concentrations (0.5–1.5 wt %). Among 10 different oligopeptides synthesized, peptide P1 (Ac–Phe–Phe–Phe–Gly–Lys) showed high gelation ability. Transmission electron microscopy observations suggested that the peptide molecules self-assembled into nanofibrous networks, which turned into gels. The hydrogel of peptide P1 showed reversible thermal gel–sol transition and viscoelastic properties typical of a gel. Circular dichroism spectra revealed that peptide P1 formed a β-sheetlike structure, which decreased with increasing temperature. The self-assembly of peptide P1 occurred even in the presence of nutrients in culture media and common surfactants. Escherichia coli and yeast successfully grew on the hydrogel. The hydrogel exhibited low cytotoxicity to animal cells. Finally, we demonstrated that functional compounds can be released from the hydrogel in different manners based on the interaction between the compounds and the hydrogel

Quantification of Amino Groups on Solid Surfaces Using Cleavable Fluorescent Compounds

We quantified amino groups displayed on inorganic and organic surfaces in aqueous solution using different types of cleavable fluorescent compounds and an aldehyde dye. The cleavable fluorescent compounds were designed to bind covalently to amino groups and then liberated under specific conditions. Among the investigated materials, cleavable coumarin was most appropriate for the quantification of amino groups on silica and resin surfaces. The developed method can measure small amounts (∼pmol/cm²) of amino groups on a flat polymeric surface, detecting only amino groups that are exposed to aqueous solution and available for surface immobilization of ligands and biomolecules

Surfactant-Induced Polymer Segregation To Produce Antifouling Surfaces via Dip-Coating with an Amphiphilic Polymer

We propose a rational strategy to control the surface segregation of an amphiphilic copolymer in its dip-coating with a low-molecular-weight surfactant. We synthesized a water-insoluble methacrylate-based copolymer containing oligo­(ethylene glycol) (OEG) (copolymer <b>1</b>) and a perfluoroalkylated surfactant (surfactant <b>1</b>) containing OEG. The dip-coating of copolymer <b>1</b> with surfactant <b>1</b> resulted in the segregation of surfactant <b>1</b> on the top surface of the dip-coated layer due to the high hydrophobicity of its perfluoroalkyl group. OEG moieties of surfactant <b>1</b> were accompanied by those of copolymer <b>1</b> in its segregation, allowing the OEG moieties of copolymer <b>1</b> to be located just below the top surface of the dip-coated layer. The removal of surfactant <b>1</b> produced the surface covered by the OEG moieties of the copolymer that exhibited antifouling properties. Using this strategy, we also succeeded in the introduction of carboxy groups on the dip-coated surface and demonstrated that the carboxy groups were available for the immobilization of functional molecules on the surface

Cancer Cell Death Induced by the Intracellular Self-Assembly of an Enzyme-Responsive Supramolecular Gelator

We report cancer cell death initiated by the intracellular molecular self-assembly of a peptide lipid, which was derived from a gelator precursor. The gelator precursor was designed to form nanofibers via molecular self-assembly, after cleavage by a cancer-related enzyme (matrix metalloproteinase-7, MMP-7), leading to hydrogelation. The gelator precursor exhibited remarkable cytotoxicity to five different cancer cell lines, while the precursor exhibited low cytotoxicity to normal cells. Cancer cells secrete excessive amounts of MMP-7, which converted the precursor into a supramolecular gelator prior to its uptake by the cells. Once inside the cells, the supramolecular gelator formed a gel via molecular self-assembly, exerting vital stress on the cancer cells. The present study thus describes a new drug where molecular self-assembly acts as the mechanism of cytotoxicity

Improvement of Antifouling Properties of Polyvinylidene Fluoride Hollow Fiber Membranes by Simple Dip Coating of Phosphorylcholine Copolymer via Hydrophobic Interactions

We present a simple surface modification method for improving the antifouling properties of polyvinylidene fluoride (PVDF) hollow fiber membranes for water treatment. Membranes were dip coated in a block copolymer of 2-methacryloyloxyethyl phosphorylcholine (MPC) and butyl methacrylate (BMA) (poly­(MPC-co-BMA)) aqueous solution. Membranes coated with poly­(MPC-co-BMA) at various coating concentrations exhibited higher antifouling properties than bare and MPC homopolymer-coated membranes, while showing higher water permeabilities after fouling. Fluorescence observation revealed the effect of coating concentration on poly­(MPC-co-BMA) distribution within the hollow fiber membranes. The results of quartz crystal microbalance measurements showed that almost no bovine serum albumin was adsorbed onto the poly­(MPC-co-BMA) coating, whereas it was highly adsorbed onto bare and MPC homopolymer coatings. We quantified the amount of poly­(MPC-co-BMA) on the membrane before and after cleaning, using fluorescence microscopy. The poly­(MPC-co-BMA) coating layer used in the hydrophobic interaction between BMA moieties and the PVDF membrane surface was quite stable