Surface-enhanced Raman scattering of 4-aminobenzenethiol in Ag sol: relative intensity of a1- and b2-type bands invariant against aggregation of Ag nanoparticles.

4-Aminobenzenthiol (4-ABT) is an unusual molecule, showing variable surface-enhanced Raman scattering (SERS) spectra depending upon measurement conditions. In an effort to reduce ambiguity and add clarity, we have thus conducted an ultraviolet-visible (UV-vis) extinction measurement, along with Raman scattering measurement, after adding 4-ABT into aqueous Ag sol. Upon the addition of 4-ABT, the surface plasmon absorption band of Ag at 410 nm gradually diminished and, concomitantly, a weak and broad band developed at longer wavelengths, obviously because of the aggregation of Ag nanoparticles. At the same time, the Raman scattering peaks of 4-ABT varied in intensity as the Ag particles proceeded to form aggregates. A close examination revealed that the peak intensity of the ring 7a band of 4-ABT, a typical a(1) vibrational mode, could be correlated with the UV-vis extinction of the Ag sol measured at the excitation laser wavelength. In a separate Raman measurement conducted using sedimented Ag colloidal particles, 4-ABT was found not to be subjected to any surface-induced photoreaction, implying that all of the observable Raman peaks were, in fact, solely due to 4-ABT on Ag. The intensities of the b(2)-type bands, such as the ring 3, 9b, and 19b modes of 4-ABT, were then analyzed and found to be invariant with respect to the 7a band, irrespective of the extent of Ag aggregation as far as at a fixed excitation wavelength. The intensity ratio of the b(2)-type/7a bands would then reflect the extent of the chemical enhancement that was involved in the SERS of 4-ABT in aggregated Ag sol.

Synthesis and characterization of a novel arginine-grafted dendritic block copolymer for gene delivery and study of its cellular uptake pathway leading to transfection.

We synthesized a novel arginine-grafted dendritic block copolymer, R-PAMAM-PEG-PAMAM-R G5 (PPP5-R) for gene delivery systems. Its Mw was measured as 2.74 x 104 Da by MALDI-TOF, and approximately 36 arginine residues are found to be grafted to the polymer by 1H NMR. PPP5-R was able to form polyplexes with plasmid DNA, the average size of which was about 200 nm. Positive zeta-potential values (+22 to +28 mV) of PPP5-R polyplex indicate the formation of positively charged stable polyplex particles and suggest that large dendritic blocks with high positive charge may not be fully shielded by PEG chains even after PEG-coated complex formation. PPP5-R polyplex shows enhanced water solubility due to the polymer's PEG core and also shows low cytotoxicity, representing the potential for in vivo application. We identified the greatly enhanced transfection efficiency of PPP5-R in comparison with that of native PPP5 on various cell lines. Moreover, in view of the result of various cellular uptake inhibitor treatments during a transfection step, the cellular uptake of PPP5-R polyplex leading to effective transfection is thought to be not dependent on one exclusive pathway and to have the possibility of multiple pathways (caveolae-, clathrin-, and macropinocytosis-mediated pathways), contrary to the caveolae-dependent uptake of the PPP5 polyplex lacking arginine residues.

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.

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.

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.

Synthesis of biodegradable cross-linked poly(beta-amino ester) for gene delivery and its modification, inducing enhanced transfection efficiency and stepwise degradation.

Biodegradable cross-linked poly(beta-amino ester) (CLPAE) was synthesized by Michael addition of pentaerythritol triacrylate and N,N-dimethylethylenediamine and modified with aminohexanoic acid and lysine to CLPAE-Ahx and CLPAE-Lys, respectively, for a gene delivery system. They could self-assemble with plasmid DNA, forming nanosized polyplexes, and CLPAE-Ahx polyplex released plasmid DNA slowly during a week through stepwise degradation. The polymers showed minimal cytotoxicity on 293 cells due to their biodegradability and biocompatibility. Transfection efficiencies of CLPAE-Ahx and CLPAE-Lys were comparable to that of PEI in 293 cells and C2C12 cells. Additionally, high transfection of CLPAE-Ahx on primary rat aorta vascular smooth muscle cells (SMC) and primary mouse embryonic fibroblast cells (MEF) shows a potential for a gene delivery system on primary cells, restenosis treatment of human SMC, and MEF cell function research. In conclusion, CLPAE-Ahx could be used as a nontoxic and highly efficient gene delivery system.

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.

Polyplexes assembled with internally quaternized PAMAM-OH dendrimer and plasmid DNA have a neutral surface and gene delivery potency.

Interior tertiary amine groups of PAMAM-OH dendrimers (hydroxyl-terminated polyamidoamine, PAMAM) were modified by methylation to make these polymers have a more cationic character, which enabled electrostatic interaction between PAMAM-OH and plasmid DNA. A methylation reaction was dose-dependent, producing internally quaternized PAMAM-OH (QPAMAM-OH), thereby making tertiary amine/quaternary amine ratio adjustment possible. More highly condensed particles of plasmid DNA were formed as the degree of quaternization increased, whereas unmodified polymer (PAMAM-OH) could not. The location of positive charges in the internal position of QPAMAM-OH resulted in the formation of neutral polyplexes in which zeta potential leveled off near the zero value even at high charge ratios (+/-) of 10. A light scattering experiment showed that the polyplex formed by QPAMAM-OH was very small with the size of 53.3 nm at the optimum condition. QPAMAM-OH/DNA polyplexes were round-shaped with the more compact and small particles formed as the charge ratio increased. QPAMAM-OH showed much reduced cytotoxicity compared with starburst PAMAM and branched polyethyleneimine (PEI) in which shielding of interior positive charges by surface hydroxyls might be the reason for this favorable result. These results suggest that QPAMAM-OH could be a promising tool as a nonviral vector both by itself and in conjugated form with targeting ligands.