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Biomedical subjects

Kwan Kim

Publications and source records attributed to Kwan Kim.

At least 19 recordsLinked to original sources
PubMed2006

Synthesis and characterization of poly (amino ester) for slow biodegradable gene delivery vector.

Many therapeutic carrier materials were exploited for human gene therapy from viral to polymeric vectors. This research describes the evaluation of two biodegradable ester-bonded polymers synthesized by double-monomer polycondensation for a non-viral cationic polymer-based gene delivery system. The backbone was constructed to include inner tertiary amines and outer primary amines. Self-assembly with DNA resulted in the production of regularly nano-sized spherical polyplexes with good transfection efficiency, especially in the presence of serum. The polymers showed a relatively slow degradability for an amine-containing ester polymer, as they maintained DNA/polymer complex for 7 days in physiological buffer conditions. Finally, the low toxicity and slow degradation concluded these polymers reliable for long-term therapeutic applications.

Buffers↗
PubMed2006

Stabilization of hydroxyl-group-terminated SERS-marker molecules on microAg particles by silanization.

Micrometer-sized Ag (microAg) powders are very efficient substrates for both the infrared and Raman spectroscopic characterization of molecular adsorbates assembled on silver. In particular, the Raman spectrum of organic monolayers on microAg powders is a surface-enhanced Raman scattering (SERS) spectrum. To use microAg powders as a core material for constructing molecular sensing/recognition units operating via SERS, it is first necessary to stabilize the SERS-marker molecules that are directly in contact with the microAg powders. One promising strategy is the fabrication of silica shells onto SERS-marker molecules, and herein we demonstrate its feasibility by choosing 4-mercaptophenol (4-MPH) as a model SERS-marker molecule. Due to the presence of the hydroxyl group of 4-MPH, silica was readily deposited onto microAg particles by the base-catalyzed hydrolysis of tetraethyl orthosilicate, and its subsequent condensation, to form a cagelike structure. The formation of silica shells was confirmed with infrared, Raman, and X-ray photoelectron spectroscopy, coupled with field emission scanning electron microscopy. We were able to tune the thickness of silica shells simply by varying the silanization reaction time.

Journal Article↗
PubMed2006

Facile method to prepare surface-enhanced-Raman-scattering-active Ag nanostructures on silica spheres.

In this paper we describe a very simple electroless plating method used to prepare Ag-coated silica beads. Robust Ag nanostructures can be reproducibly fabricated by soaking silica beads in ethanolic solutions of AgNO(3) and butylamine. When the molar ratio of butylamine to AgNO(3) is far below 1.0, distinct nanosized Ag particles are formed on the silica beads, but by increasing the amount of butylamine, network-like Ag nanostructures are formed that possess very broad UV/vis absorption characteristics extending from near-UV to near-infrared regions. In conformity with the UV/vis absorption characteristics, the Ag-deposited silica beads were highly efficient surface-enhanced Raman scattering (SERS) substrates, with the enhancement factor estimated using benzenethiol as a model adsorbate to be larger than 10(6). Since another silica layer can be readily deposited onto the Ag surface, the Ag-coated silica beads should be invaluable in the development of SERS-based biosensors.

Journal Article↗
PubMed2006

microAg particle-based molecular sensing/recognition via surface-enhanced Raman spectroscopy.

In this study, we demonstrate that powders of commercially available 2-microm-sized Ag (microAg) can be used as a core material for constructing molecular sensing/recognition units operating via surface-enhanced Raman scattering (SERS). This is possible because microAg powders are very efficient substrates for both the infrared and Raman-spectroscopic characterization of molecular adsorbates prepared in a similar manner on silver surfaces. The Raman spectrum of organic monolayers on powdered silver is a SERS spectrum. The agglomeration of microAg particles in a highly concentrated buffer solution could be prevented by the deposition of polar molecules like 1,4-phenylenediisocyanide (1,4-PDI), and mixed self-assembled monolayers of 1,4-PDI and N-(+)-biotinyl-6-aminocaproic acid on microAg particles were then confirmed via the SERS of 1,4-PDI to selectively recognize the avidin arrays formed on a separate biotinylated substrate. According to a dose response curve, avidin at >10(-6)g/mL could be easily identified by the present method. In addition, the non-specific adsorption of microAg particles was found to be negligibly small, probably because the Ag particles were too heavy to be retained on organic substrates solely by non-specific interaction.

Avidin↗
PubMed2006

Silver-particle-based surface-enhanced Raman scattering spectroscopy for biomolecular sensing and recognition.

In this study, we demonstrate that 2-microm-sized Ag (microAg) powders can be used as a core material for constructing molecular sensing/recognition units operating via surface-enhanced Raman scattering (SERS). This is possible because microAg powders are very efficient substrates for both the infrared and Raman-spectroscopic characterization of molecular adsorbates prepared in a similar manner on silver surfaces; we can obtain an infrared spectrum of organic molecules adsorbed on microAg particles with a very high signal-to-noise ratio by diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), and the Raman spectrum of organic monolayers on powdered silver is an SERS spectrum. The agglomeration of microAg particles in a highly concentrated buffer solution could be prevented by the layer-by-layer deposition of cationic and anionic polyelectrolytes such as poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA). In fact, prior to depositing PAA and PAH, 4-aminobenzenethiol (4-ABT) was assembled on the surfaces of the microAg particles as SERS markers. Because of the presence of amine groups of 4-ABT, PAA could be readily deposited on the microAg particles. On the other hand, the outermost PAA layer could also be derivatized with biotin-derivatized poly(L-lysine). The nonspecific interaction of poly(L-lysine) with proteins could be suppressed by grafting poly(ethylene glycol) into the biotin-derivatized poly(L-lysine) molecules. On the basis of the nature of the SERS peaks of 4-ABT, it was confirmed that these biotinylated microAg powders were effective in selectively recognizing the streptavidin arrays. Because a number of different molecules can be used as SERS-marker molecules, such as probable 4-ABT, commercially available microAg powders must be a prospective material in molecular sensing/recognition, particularly via SERS.

Acrylic Resins↗
PubMed2006

Assembly of metal nanoparticle-carbon nanotube composite materials at the liquid/liquid interface.

Carbon nanotubes (CNTs)-mediated self-assembly of metal (Au and Ag) nanoparticles at the liquid/liquid interface in the form of a stable nanocomposite film is reported. The metallic luster results from the electronic coupling of nanoparticles, suggesting the formation of closely packed nanoparticle thin films. The interfacial film could be transferred to mica substrates and carbon-coated transmission electron microscopy (TEM) grids. The transferred films were very stable for a prolonged time. The samples were characterized by UV-vis spectroscopy, scanning electron microscopy (SEM), TEM, and X-ray photoelectron spectroscopy (XPS). SEM and TEM results show that the films formed at the liquid/liquid interface are indeed composite materials consisting of CNTs and nanoparticles. XPS measurements further indicate the presence of the interaction between nanoparticles and CNTs.

Journal Article↗
PubMed2006

Novel fabrication of Ag thin film on glass for efficient surface-enhanced Raman scattering.

This paper describes a very simple electroless-plating method used to prepare optically tunable nanostructured Ag films. Very stable Ag films can be reproducibly fabricated simply by soaking glass substrates in ethanolic solutions of AgNO3 and butylamine. The grain size of silver can be readily controlled to range from 20 to 150 nm, and these nanostructural features correlated well with their UV/vis absorption characteristics, as well as with their surface-enhanced Raman scattering (SERS) activities. It is also very advantageous that the Ag films prepared exhibit very even SERS activity over an area up to hundreds thousand square-micrometers, and the enhancement factor estimated using benzenethiol as a prototype adsorbate reaches approximately 2 x 10(5). Since the proposed method is cost-effective and is suitable for the mass production of diverse Ag films irrespective of the shapes of the underlying substrates, it is expected to play a significant role in the development of surface plasmon-based analytical devices.

Journal Article↗
PubMed2006

Adsorption characteristics of arylisocyanide on Au and Pt electrode surfaces: surface-enhanced Raman scattering study.

It is very important to understand metal-molecule interface characteristics for the development of efficient molecular wires in molecular electronics. Because isocyanide is potentially a good alligator clip, we have investigated in this work the adsorption characteristics of 2,6-dimethylphenylisocyanide (DMPI) on Au and Pt electrodes by recording the potential-dependent surface-enhanced Raman scattering (SERS) spectra. First of all, we confirmed that Pt nanoaggregate films were efficient SERS-active substrates, not only in ambient conditions, but also in electrochemical environments. Second, we confirmed that aryl isocyanide should adsorb on Au and Pt by forming exclusively metal-CN bonds, via a pure sigma type interaction in the case of gold compared with a sigma/pi synergistic interaction on Pt. This implies that DMPI should adsorb on Au only via the on-top site, whereas not only the on-top site, but also the 2-fold bridge and 3-fold hollow sites, could be used in the surface adsorption of DMPI on Pt. Despite these differences, DMPI was assumed to possess a vertical orientation with respect to the Au and Pt substrates, irrespective of the potential variation between +0.2 and -0.6 V relative to the Ag/AgCl reference electrode. The latter characteristics of the Au-CN and Pt-CN combinations are presumed to be useful in designing molecular-scale wires.

Journal Article↗
PubMed2006

Light stamping lithography: microcontact printing without inks.

We report a new patterning method, called light-stamping lithography (LSL), that uses UV-induced adhesion of poly(dimethylsiloxane) (PDMS). LSL is based on the direct transfer of the contact surface of the PDMS stamp to a substrate via a UV (254 nm)-induced surface bonding between the stamp and the substrate. This procedure can be adopted in automated printing machines that generate patterns with a wide range of feature sizes on diverse substrates. To demonstrate its usefulness, the LSL method was applied to prepare several PDMS patterns on a variety of substrates. The PDMS patterns were then used as templates for selective deposition of TiO2 thin film using atomic layer deposition as well as resists for selective wet etching.

Journal Article↗
PubMed2005

Highly effective and slow-biodegradable network-type cationic gene delivery polymer: small library-like approach synthesis and characterization.

Over the past years, macromolecular biodegradable polymers have been attracting considerable attention as gene delivery vehicles due to their safety and many potential applications. In the process of developing such biopolymers, we synthesized a biodegradable, network-type poly(amino ester) polymer (nt-PAE), which showed desirable chemical properties and a mechanical durability with high transfection efficiency. A small library-like approach to polymer synthesis using melt polycondensation followed by surface modification with aminohexanoic acid resulted in the final polymer, nt-PAE. The network-type structure of nt-PAE consists of biodegradable ester linkages and tertiary amines embedded in the backbone, and primary amines positioned at the surface. Unlike other rapidly degrading ester polymers, the nt-PAE exhibited fairly slow degradation, as the polymer sustained its DNA complexing ability for 10 days under physiological buffer conditions. In addition, the transfection efficiency of the nt-PAE could be increased to the same level comparable with that of PEI even in the presence of serum. Low toxicity and high transfection efficiency with a slow degradation profile implies that the nt-PAE can be used as a valuable nonviral gene delivery system.

Biocompatible Materials↗
PubMed2005

Raman scattering of 4-aminobenzenethiol sandwiched between Ag/Au nanoparticle and macroscopically smooth Au substrate.

Raman scattering measurements were conducted for a 4-aminobenzenethiol (4-ABT) monolayer assembled on a macroscopically smooth Au substrate. Although no peak was detected at the beginning, Raman peaks were distinctly observed by attaching Ag or Au nanoparticles onto the 4-ABT monolayer (Ag(Au)@4-ABT/Au(flat)). Considering the fact that no Raman signal is observed when Ag (Au) nanoparticles are adsorbed on a (4-aminophenyl)silane monolayer assembled on a silicon wafer, the Raman spectrum observed for Ag(Au)@4-ABT/Au(flat) must be a surface-enhanced Raman scattering (SERS) spectrum, derived from the electromagnetic coupling of the localized surface plasmon of Ag (Au) nanoparticles with the surface plasmon polariton of the underneath Au metal. The electromagnetic coupling responsible for SERS appeared to be governed more by the bulk Au substrate than the sparsely distributed Ag or Au nanoparticles. The chemical enhancement appeared on the other hand to be derived more from the formation of Au-S bonds than any charge-transfer interaction between the protonated amine group and the Au or Ag nanoparticles. The enhancement factors derived from the attachment of a single Ag or Au nanoparticle onto 4-ABT on Au were estimated to be as large as 8.3 x 10(5) and 5.0 x 10(5), respectively, (for the ring 3 band (b(2)) near 1390 cm(-1)) in which a factor of approximately 10(2) was presumed to be due to the chemical effect, with the remaining contributed by the electromagnetic effect.

Journal Article↗
PubMed2005

Effect of Ag and Au nanoparticles on the SERS of 4-aminobenzenethiol assembled on powdered copper.

Raman scattering measurements were conducted for 4-aminobenzenethiol (4-ABT) assembled on powdered copper substrates. Initially, very weak Raman peaks were detected, but upon attaching Ag nanoparticles probably via NH2 groups onto 4-ABT/Cu, distinct Raman spectra were observed. Considering the fact that no Raman peak was identified when Ag nanoparticles were adsorbed on 4-aminophenyl-derivatized silane monolayers assembled on silica powders, the Raman spectra observed for Ag@4-ABT/Cu should be surface-enhanced Raman scattering (SERS) spectra, occurring by an electromagnetic coupling of the localized surface plasmon of Ag nanoparticles with the surface plasmon polariton of Cu powders. The extra enhancement factor attainable by the attachment of a single Ag nanoparticle is estimated to be as large as 1.4 x 10(5) in the case when 632.8-nm radiation is used as the excitation source. When Au nanoparticles were attached onto 4-ABT/Cu, at least an order of magnitude weaker Raman spectra were obtained at all excitation wavelengths, however, indicating that the Au-to-Cu coupling should be far less effective than the Ag-to-Cu coupling for the induction of SERS.

Copper↗
PubMed2004

Characterization of DNA immobilization and subsequent hybridization using in situ quartz crystal microbalance, fluorescence spectroscopy, and surface plasmon resonance.

We have characterized the immobilization of thiol-modified oligomers on Au surfaces and subsequent hybridization with a perfectly matched or single-base mismatched target using a quartz crystal microbalance (QCM) and fluorescence spectroscopy. The surface density of immobilized probe molecules and the hybridization efficiency depending on the type of buffer and salt concentration were investigated. We observed some ambiguities in surface coverage deduced from QCM measurement and adopted a complementary fluorescence displacement method. Direct comparison of surface coverage deduced from frequency change in QCM measurement and determined by the fluorescence exchange reaction revealed that QCM results are highly overestimated and the amount of overestimation strongly depends on the type of buffer and the structure of the film. Discrimination capability of the surface attached 15-mer probe was also examined using a single-base mismatched target at various hybridization temperatures. Hybridization efficiency depending on the type of single base mismatch was investigated using surface plasmon resonance (SPR).

DNA↗
PubMed2004

Influence of liquid medium and surface morphology on the response of QCM during immobilization and hybridization of short oligonucleotides.

With the goal of developing a quartz crystal microbalance (QCM)-based DNA sensor, we have conducted an in situ QCM study along with fluorescence measurements using oligonucleotides (15-mer) as a model single-stranded DNA (ss-DNA) in two different aqueous buffer solutions; the sequence of 15-mer is a part of iduronate-2-sulphate exon whose mutation is known to cause Hunter syndrome, and the 15-mer is thiolated to be immobilized on the Au-coated quartz substrate. The fluorescence data indicate that the initial immobilization as well as the subsequent hybridization with a complementary strand is hardly dependent on the kind of buffer solution. In contrast, the mass increases deducible from the decrease of QCM frequency via the Sauerbrey equation are 2.7-6.2 and 3.0-4.4 times larger than the actual mass increases, as reflected in the fluorescence measurements, for the immobilization and the subsequent hybridization processes, respectively. Such an overestimation is attributed to the trapping of solvent as well as the formation of quite a rigid hydration layer associated with the higher viscosities and/or densities of the buffer solutions. Another noteworthy observation is the excessively large frequency change that occurs when the gold electrode is deposited in advance with Au nanoparticles. This clearly illustrates that the QCM detection of DNA hybridization is also affected greatly by the surface morphology of the electrode. These enlarged signals are altogether presumed to be advantageous when using a QCM system as an in situ probing device in DNA sensors.

Adsorption↗
PubMed2004

Chemical lithography by Ag-nanoparticle-mediated photoreduction of aromatic nitro monolayers on Au.

Patterned, amine-terminated monolayers can be fabricated from 4-nitrobenzenethiol (4-NBT) monolayers simply by irradiating under ambient conditions with visible laser after spreading Ag nanoparticles onto selected regions of the 4-NBT monolayers on Au. Au nanoparticles were adsorbed selectively onto the amine groups produced by photoreaction, and polyaniline was found to grow exclusively at the amine groups when electrochemical polymerization was conducted using the patterned substrate as the working electrode. These observations clearly support our previous contention that Ag nanoparticles can act as moderate photoelectron emitters.

Letter↗
PubMed2004

Gelation of octadecyltrimethoxysilane at the air/water interface: effect of perfluorotetradecanoic acid and divalent cadmium ions.

The effect of an acidic surfactant, perfluorotetradecanoic acid (PFTDA), on the gelation of octadecyltrimethoxysilane (ODTMS) monolayers at the air/water interface was investigated using a Langmuir film balance, attenuated total reflection (ATR) infrared spectroscopy, and atomic force microscopy (AFM). The gelation of ODTMS was greatly accelerated by adding only 2 mol % PFTDA into the monolayer; in this case, the hydrolysis of ODTMS was completed within a few minutes, whereas otherwise it took 18 h. ATR-IR spectroscopy clearly demonstrated that the gelation of a 49:1 ODTMS/PFTDA monolayer proceeded on a pure water subphase mainly via hydrolysis followed by condensation. In the presence of PFTDA, the local acidity at specific sites is presumed to be very high, catalyzing the hydrolysis of ODTMS. The extremely fast rate is attributed not only to the lateral diffusion of PFTDA in the mixed monolayer but also to proton propagation where the proton(s) involved in the initial hydrolysis are transposed rapidly to the nearby methoxy groups for subsequent hydrolysis. The catalytic activity of PFTDA can be neutralized, however, simply by the addition of multivalent metallic ions such as Cd2+ to form saltlike complexes with PFTDA; the rate of 2-D sol-gel processes can thus be easily regulated by a minute amount of PFTDA and/or Cd2+ added into the reaction system.

Journal Article↗
PubMed2004

Size-dependent adsorption of 1,4-phenylenediisocyanide onto gold nanoparticle surfaces.

Adsorption of 1,4-phenylenediisocyanide (PDI) has been studied for different-sized gold nanoparticles with mean diameters of 6, 14, 23, 40, 57, and 97 nm using UV-vis absorption spectroscopy and surface-enhanced Raman scattering (SERS). The SERS enhancement was found to be relatively weak for 6-nm particles due to less aggregation between PDI and gold particles. Concentration-dependent SERS spectra show that PDI was assumed to bridge two different gold particles at low concentrations of PDI, but as the concentration was increased, the bridge appeared to be broken, and PDI bonded to the gold particle only via one of its two isocyanide groups. For the 57- and 97-nm particles, however, the nu(NC)(free) stretching band in the SERS spectrum almost disappeared, even at a high bulk concentration of PDI, differently from the case of the smaller sizes (14, 23, and 40 nm). The 57- and 97-nm particles appeared to cross-link through the pendent isocyanide group even at a high bulk concentration. UV-vis absorption spectra indicated that PDI appeared to aggregate more extensively with increasing size in agreement with Raman data. Our result shows an example that the adsorption scheme of an aromatic diisocyanide may be varied depending on particle size as well as the bulk concentration.

Journal Article↗