34 research outputs found
Highly efficient non-biofouling coating of zwitterionic polymers: Poly((3-(methacryloylamino)propyl)-dimethyl(3-sulfopropyl)ammonium hydroxide)
No full textThis work describes the formation of highly efficient non-biofouling polymeric thin films of poly((3-(methacryloylamino)propyl)-dimethyl(3-sulfopropyl)ammonium hydroxide), (poly(MPDSAH)). The poly(MPDSAH) films were generated from the self-assembled monolayers terminating in an initiator of atom transfer radical polymerization (ATRP) by the surface-initiated ATRP of MPDSAH. The poly(MPDSAH) films on a gold surface were characterized by ellipsometry, FT-IR spectroscopy, contact angle goniometery, and X-ray photoelectron spectroscopy. The copper complexes and unpolymerized monomers trapped inside the polymer brushes were completely washed out by soaking the poly(MPDSAH)-coated substrate in water at 40 degrees C for 4 days. The amount of proteins nonspecifically adsorbed onto the poly(MPDSAH) films was evaluated by surface plasmon resonance spectroscopy: the adsorption of proteins was < 0.6 ng/cm(2) on the surfaces for all the model proteins. The ability of the poly(MPDSAH) films to resist the nonspecific adsorption of proteins was comparable to that of the best known systems
Surface-initiated, ring-opening metathesis polymerization: Formation of diblock copolymer brushes and solvent-dependent morphological changes
No full textIn this article, we report the formation of diblock copolymer brushes on a gold surface by surface-initiated, ring-opening metathesis polymerization (SI-ROMP) with the newly developed ruthenium catalyst [(H(2)IMes)(3-Br-py)(2)(Cl)(2)RuCHPh]. Taking advantage of the highly improved activity of the ruthenium catalyst and the rapid initiation step of ROMP, we successfully formed thin films of well-defined block copolymers with 5-norbornene-2-endo,3-endo-dimethanol and norbornene carboxylic acid methyl esters (44:56 endo/exo). The catalyst was found to be active enough to polymerize endo isomers of norbonene derivatives from the surface as well as to form diblock copolymer brushes. SI-ROMP of diblock copolymers from the surface was confirmed by ellipsometry, infrared spectroscopy, and X-ray photoelectron spectroscopy. After the formation, the polymer-grafted substrates were immersed in various solvents, and the selective swelling characteristics of polymer brushes were investigated by atomic force microscopy
Formation of thermoresponsive gold nanoparticle/PNIPAAm hybrids by surface-initiated, atom transfer radical polymerization in aqueous media
No full textWe investigated the formation of thermoresponsive gold nanoparticle/poly(N-isopropylacrylamide) (AuNP/ PNIPAAm) core/shell hybrid structures by surface-initiated, atom transfer radical polymerization (SI-ATRP) in aqueous media and the effect of cross-linking on the thermoresponsiveness of the AuNP/PNIPAAm hybrids. The disulfide containing an ATRP initiator was attached onto AuNPs and the monomer, NIPAAm, was polymerized from the surface of AuNPs in the absence or presence of a cross-linker, ethylene diacrylate, in aqueous media at room temperature. The resulting brush-type and cross-linked AuNP/PNIPAAm hybrids were characterized by Fourier-transform infrared spectroscopy, transmission electron microscopy, and variable temperature dynamic light scattering
The control of cell adhesion and detachment on thin films of thermoresponsive poly[(N-isopropylacrylamide)-r-((3-(methacryloylamino)propyl)-dimethyl(3-sulfopropyl)ammonium hydroxide)]
No full textThis paper describes the formation of poly(N-isopropylacrylamide) (PNIPAAm) and poly[(N-isopropylacrylamide)-r-((3-(methacryloylamino)propyl)-dimethyl(3-sulfopropyl)ammonium hydroxide)] (P(NIPAAm-r-MPDSAH)) films on a glass surface via surface-initiated, atom transfer radical polymerization as a cell-culture platform. The films of PNIPAAm with various thicknesses and of P(NIPAAm-r-MPDSAH) with various ratios of NIPAAm and MPDSAH are formed to investigate the behaviors of cell adhesion and detachment. In the case of the PNIPAAm-grafted glass surfaces, the optimal film thickness, achieving the effective control of both cell adhesion and detachment, is estimated to be 11-13 nm for NIH 3T3 fibroblast cells. The adhesion and detachment behaviors of NIH 3T3 fibroblast cells are further tuned by incorporating the hydrophilic and non-biofouling MPDSAH moiety into the PNIPAAm system. The cell adhesion and detachment are controlled best, when the ratio of NIPAAm and MPDSAH is 75:1 (NIPAAm:MPDSAH). (C) 2009 Elsevier Ltd. All rights reserved
Formation of thermoresponsive surfaces by surface-initiated, aqueous atom-transfer radical polymerization of N-isopropylacrylamide: Application to cell culture
No full textPolymeric Rulers: Distance‐Dependent Emission Behaviors of Fluorophores on Flat Gold Surfaces and Bioassay Platforms Using Plasmonic Fluorescence Enhancement
No full textIn this paper, we introduce the concept of a "polymeric ruler" for investigating distance-dependent emission behaviors of fluorophores, namely the quenching or enhancement of fluorescence, on flat Au surfaces in the range of 5 to similar to 100 nm, which has not previously been easily accessible. The polymeric ruler is constructed by a highly controllable surface-initiated atom transfer radical polymerization of oligo(ethylene glycol)methacrylate (OEGMA), and the obtained thicknesses of the poly(OEGMA) (pOEGMA) layers range from similar to 5 to similar to 80 nm. The quenching or enhancement of fluorescence is found to be dependent upon the distance between fluorophores and the Au surface. In brief, fluorescence quenching occurs at distances within about 15 nm from the Au surface, and surface-enhanced fluorescence is observed at tens of nanometers beyond the range of quenching with the maximum enhancement at about 40-50 nm. The obtained information on the distance-dependent surface-enhanced fluorescence is applied to the construction of highly sensitive bioassay platforms: the use of the 50 nm thick pOEGMA layer lowers the detection limit up to 1 pM.
금 표면에 형성된 자기조립막의 pH에 따른 안정성 연구.
No full text학위논문(박사) - 한국과학기술원 : 화학과, 2010.2, [ x, 123 p. ]Part I reports the effect of pH on the stability of self-assembled monolayers (SAMs) of various alkanethiols with different terminal groups on gold. The SAMs of 1-hexadecanethiol , 16-mercaptohexadecanol , 16-mercaptohexadecanoic acid and 16-amino-1-hexadecanethiol were prepared, and their stability was investigated at pH values from 1 to 14 for one week. The ellipsometric measurements showed that these SAMs were unstable under highly basic conditions. For example, the thickness of all the four SAMs decreased rapidly within one day at pH 14. At the pH values of 13 and 13.5, the SAMs of were found to be stable, while the thickness of the three other SAMs decreased gradually. The SAMs remained stable at pH 12 and below, and no thickness decrease was observed even at pH 1 and 2.
Part II describes the studies of polymer-grafted surfaces and their chemical and biological applications. To generate the surfaces with special functionality, stimuli-responsive polymers and highly protein/cell resistent polymers were used to form surface-tethered polymer brushes. Various polymerization methods such as ring-opening metatheis polymerization and atom transfer radical polymeriation were adopted to form the polymer brushes on numerous substrates, including gold, silicon oxide, and glass. Polymer-grafted surfaces with the special functionality were then applied for selective morphological switching of the surface, effective cell culture surface, and powerful protein/cell-resistent surface maintaining the original form of cell micropatterns.
In Chapter 1, we reported the formation of diblock copolymer brushes on a gold surface by surface-initiated, ring-opening metathesis polymerization (SI-ROMP) with the newly developed ruthenium catalyst, . Taking advantage of the highly improved activity of the ruthenium catalyst and the...한국과학기술원 : 화학과
Posterior concentrations of fully-connected Bayesian neural networks with general priors on the weights
No full textBayesian approaches for training deep neural networks (BNNs) have received
significant interest and have been effectively utilized in a wide range of
applications. There have been several studies on the properties of posterior
concentrations of BNNs. However, most of these studies only demonstrate results
in BNN models with sparse or heavy-tailed priors. Surprisingly, no theoretical
results currently exist for BNNs using Gaussian priors, which are the most
commonly used one. The lack of theory arises from the absence of approximation
results of Deep Neural Networks (DNNs) that are non-sparse and have bounded
parameters. In this paper, we present a new approximation theory for non-sparse
DNNs with bounded parameters. Additionally, based on the approximation theory,
we show that BNNs with non-sparse general priors can achieve near-minimax
optimal posterior concentration rates to the true model
Design and fabrication of integrated passive valves and pumps for flexible polymer 3-dimensional microfluidic systems
No full textThis paper describes the fabrication of flexible, polymeric 3-dimensional microfluidic systems with integrated check valves (flap and diaphragm valves) and a pump by stacking patterned poly(dimethylsiloxane) (PDMS) layers containing microchannels and vias. We describe this procedure for fabricating, manipulating, and bonding of PDMS membranes and bas-relief plates into multilayer microfluidic devices. The fabrication and demonstration of integrated check valves and a pump in a prototype polymer 3-dimensional microfluidic system is a step toward practical realization of all-polymer, flexible, low-cost, disposable microfluidic devices for biochemical applications.</p
