Joonseok Koh

Dye/Peroxalate Aggregated Nanoparticles with Enhanced and Tunable Chemiluminescence for Biomedical Imaging of Hydrogen Peroxide

Hydrogen peroxide (H(2)O(2)) is an endogenous molecule that plays diverse physiological and pathological roles in living systems. Here we report multimolecule integrated nanoprobes with the enhanced chemiluminescence (CL) response to H(2)O(2) that is produced in cells and in vivo. This approach is based on the nanoscopic coaggregation of a dye exhibiting aggregation-enhanced fluorescence (AEF) with a H(2)O(2)-responsive peroxalate that can convert chemical reaction energy into electronic excitation. The coaggregated CL nanoparticles (FPOA NPs) with an average size of ~20 nm were formulated by aqueous self-assembly of a ternary mixture of a surfactant (Pluronic F-127) and concentrated hydrophobic dye/peroxalte payloads. Spectroscopic studies manifest that FPOA NPs as a reagent-concentrated nanoreactor possess the signal enhancement effect by AEF, as well as the optimized efficiencies for H(2)O(2) peroxalate reaction and subsequent intraparticle energy transfer to the dye aggregates, to yield greatly enhanced CL generation with a prolonged lifetime. It is shown that the enhanced CL signal thereby is capable of detecting intracellular H(2)O(2) overproduced during immune response. We also demonstrate that the densely integrated nature of FPOA NPs facilitates further intraparticle CL energy transfer to a low-energy dopant to red shift the spectrum toward the biologically more transparent optical window, which enables the high-sensitivity in vivo visualization of H(2)O(2) associated with early stage inflammation.

Physiochemical, Optical and Biological Activity of Chitosan-Chromone Derivative for Biomedical Applications

This paper describes the physiochemical, optical and biological activity of chitosan-chromone derivative. The chitosan-chromone derivative gels were prepared by reacting chitosan with chromone-3-carbaldehyde, followed by solvent exchange, filtration and drying by evaporation. The identity of Schiff base was confirmed by UV-Vis absorption spectroscopy and Fourier-transform infrared (FTIR) spectroscopy. The chitosan-chromone derivative was evaluated by X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), photoluminescence (PL) and circular dichroism (CD). The CD spectrum showed the chitosan-chromone derivative had a secondary helical structure. Microbiological screening results demonstrated the chitosan-chromone derivative had antimicrobial activity against Escherichia coli bacteria. The chitosan-chromone derivative did not have any adverse effect on the cellular proliferation of mouse embryonic fibroblasts (MEF) and did not lead to cellular toxicity in MEFs. These results suggest that the chitosan-chromone derivative gels may open a new perspective in biomedical applications.

Physiochemical and optical properties of chitosan based graphene oxide bionanocomposite.

In the present investigation an ecofriendly approach and a simple homogeneous solution casting method led to the development of biodegradable chitosan/graphene oxide bionanocomposites. The formation of bionanocomposite was confirmed by UV-vis, FT-IR, Raman spectroscopy, XRD, and further evaluated by thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The circular dichroism (CD) study of chitosan/graphene oxide revealed that the intensity of the negative transition band at wavelength of 200-222 nm decreased with the different pH of chitosan/graphene oxide solutions. It was also found that the pH conditions affect the interaction between chitosan and graphene oxide. Optical properties of chitosan/graphene oxide are evaluated by photoluminescence (PL) spectroscopy which showed blue shift at excitation wavelength of 255 nm compared to graphene oxide. These results strongly suggest that the bionanocomposite materials may open new vistas in biotechnological, biosensor and biomedical applications.

A new chitosan-thymine conjugate: Synthesis, characterization and biological activity

Conjugation of chitosan with nucleobases is expected to expand its not only antimicrobial activity but also anti-cancer activity. Here, we report the synthesis of a novel chitosan-thymine conjugate by the reaction between chitosan and thymine-1-yl-acetic acid followed by acylation. The synthesized conjugate was characterized by FTIR, XRD, (1)H NMR, TGA and SEM. The microbiological screening results demonstrated the antimicrobial activity of the conjugate against bacteria viz., Escherichia coli, Staphylococcus aureus, and fungi viz., Aspergillus niger. The chitosan-thymine conjugate also inhibited (p<0.05) the proliferation of human liver cancer cells (HepG2) in a dose-dependent manner but had no cellular toxicity in non-cancerous mouse embryonal fibroblast cells (NIH 3T3). Thus, the chitosan-nucleobase conjugate may open a new perspective in biomedical applications.

Gadolinium-coordinated elastic nanogels for in vivo tumor targeting and imaging.

Coordination polymer gels have been recognized as promising hybrid nanoplatforms for imaging and therapeutic applications. Here we report functional metal-organic coordinated nanogels (GdNGs) for in vivo tumor imaging, whose non-crystalline and elastic nature allows for long blood circulation, as opposed to the rapid systemic clearance of common nanohybrids with rigid/crystalline frameworks. The deformable structure of GdNGs was constructed by random crosslinking of highly flexible polyethyleneimines (PEI) with gadolinium (Gd(3+)) coordination. The in vitro characterization revealed that GdNGs have elasticity with an apparent Youngs modulus of 3.0 MPa as well as minimal cytotoxicity owing to the tight chelation of Gd(3+) ions. In contrast to common T1-enhancing gadolinium complexes, GdNGs showed the capability of enhancing negative T2 contrast (r2 = 82.6 mm(-1)s(-1)) due to the Gd(3+)-concentrated nanostructure. Systemic administration of fluorescently labeled GdNGs with core and overall hydrodynamic sizes of ~65 and ~160 nm manifested efficient targeting and dual-modality (magnetic resonance/fluorescence) imaging of tumor in a mouse model. The minimal filtration by the reticuloendothelial system (RES) suggests that the structural deformability helps the large colloids circulate in the blood stream for tumor accumulation. The unusual performance of a large Gd(3+)-complexed colloid (minimal RES sequestration and high T2 contrast enhancement) represents the versatile nature of nanoscopic organic-inorganic hybridization for biomedical applications.

Tuning Solid-State Fluorescence to the Near-Infrared: A Combinatorial Approach to Discovering Molecular Nanoprobes for Biomedical Imaging

Dyes showing solid-state fluorescence (SSF) are intriguing molecules that can emit bright fluorescence in the condensed phase. Because they do not suffer from self-quenching of fluorescence, nanoscopic dense integration of those molecules produces particulate nanoprobes whose emission intensity can be boosted by raising the intraparticle dye density. In spite of the potential promise for imaging applications demanding intense emission signals, their excitation and emission spectra are generally limited to the visible region where biological tissues have less transparency. Therefore, the SSF-based nanoprobes have rarely been applied to noninvasive in vivo imaging. Here we report a combinatorial chemistry approach to attain a high level of tissue transparency of SSF by tuning its excitation and emission wavelengths to the truly near-infrared (NIR) region. We built a dipolar arylvinyl (ArV) scaffold-based chemical library where the optical bandgap could be narrowed to the NIR above 700 nm by combinatorial modulation of the π-electron push-pull strengths. The ArV-aggregated nanoparticles (FArV NPs) with a colloidal size less than 20 nm were formulated using a polymeric surfactant (Pluronic F-127) and applied to bioimaging in cells and in vivo. We demonstrate that some of FArV NPs have truly NIR excitation and emission of SSF, capable of noninvasive in vivo imaging (efficient lymph node mapping and early diagnosis of tumor) in mouse models by virtue of bright solid-state NIR fluorescence and high signal-to-background contrast (S/B ≈ 8) as well as facile circulation in the living body.

Chitosan Biopolymer Schiff Base: Preparation, Characterization, Optical, and Antibacterial Activity

Natural biopolymer used for hydrogels has attracted increasing attention in the multifaceted areas of biomedical science and engineering. The authors prepared chitosan biopolymer Schiff base by solvent exchange method using a simple aliphatic crosslinker, crotanaldehyde. The identity of Schiff base was confirmed by UV-vis and Fourier-transform infrared spectroscopy. The chitosan Schiff base was evaluated by XRD, TGA, DSC, and SEM. The microbiological screening results demonstrated the antibacterial activity of Schiff base against Escherichia coli and Staphylococcus aureus bacteria. These results suggest that the newly prepared Schiff base may open a new perspective in biomedical applications.

Physiochemical and optical study of chitosan–terephthaldehyde derivative for biomedical applications

The chitosan-terephthaldehyde derivative was prepared by conversion of the chitosan gels through the extraction of the solvent, filtration and drying, a greener technique used for processing the materials. The identity of Schiff base was confirmed by UV-vis and Fourier-transform infrared (FTIR) spectroscopy. The chitosan-terephthaldehyde derivative was evaluated by X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), photoluminescence (PL) and rheological study. Photoluminescence (PL) spectrum had shown red shifted at excitation wavelength 254 nm. The rheological study revealed satisfactory behaviour which demonstrates better fluidity as well as moderate viscoelastic strength of the prepared gel. These results suggest that the chitosan-terephthaldehyde derivative material may open a new perspective in biomedical applications.

Dyeing and fastness properties of a reactive disperse dye on PET, nylon, silk and N/P fabrics

Dyeing and color fastness properties of a reactive disperse dye containing an acetoxyethylsulphone group on PET, Nylon, silk and N/P fabrics were examined. The reactive disperse dye exhibited almost the same dyeing properties on PET fabric as a conventional disperse dye except the level of dye uptake. The most appropriate pH and dyeing temperature for the dyeing of Nylon fabric were 7 and 100°C respectively. The build-up on Nylon fabric was good and various color fastnesses were good to excellent due to the formation of the covalent bond. Application of the reactive disperse dye on silk fabric at pH 9 and 80°C yielded optimum color strength. The rate of dyeing on Nylon fabric was faster than that on PET fabric when both fabrics were dyed simultaneously in a dye bath, accordingly color strength of the dyed Nylon was higher. The reactive disperse dye can be applied for one-step and one-bath dyeing of N/P mixture fabric with good color fastness.

Effect of pineapple protease on the characteristics of protein fibers

A pineapple protease, bromelain, was used to improve the dyeing properties of protein fibers such as wool and silk. The optimal condition for the activity of the pineapple protease was about 60 °C at pH 7. The wool and silk were treated with the protease extracted from a pineapple and the K/S values of the dyed wool and silk were measured using a spectrophotometer in order to compare the dye uptake. The protease treatment enhanced the dyeing properties of protein fibers without severe changes in mechanical properties. The surface appearances of protease-treated fibers were observed by microscopy.