Kyusik Yun

Biosynthesis of silver nanoparticles by Streptomyces hygroscopicus and antimicrobial activity against medically important pathogenic microorganisms.

Biological reduction of aqueous silver ions by extracellular components of Streptomyces hygroscopicus has facilitated the development of industrially viable greener methods for the synthesis of technologically important silver nanoparticles (AgNPs). The synthesized aqueous products showed the characteristic absorption spectra at 420 nm, which confirmed the presence of AgNPs. X-ray diffraction patterns displayed typical peaks of crystalline silver at approximately 38 degrees , approximately 45 degrees and approximately 65 degrees . The AgNPs were determined to be spherical (20-30 nm) with a purity of 70% as determined by FE-SEM, TEM, bio-AFM, XRD, and energy dispersive X-ray analysis. Furthermore, the biosynthesized AgNPs significantly inhibited the growth of medically important pathogenic gram-positive bacteria (Bacillus subtilis and Enterococcus faecalis), gram-negative bacteria (Escherichia coli and Salmonella typhimurium) and yeast (Candida albicans). Thus, bioconversion of silver nanoparticles by S. hygroscopicus could be employed as a potential nanomedicine to eliminate pathogenic microorganisms.

Fluorescent Gold Nanoclusters for Selective Detection of Dopamine in Cerebrospinal fluid

Since the last two decades, protein conjugated fluorescent gold nanoclusters (NCs) owe much attention in the field of medical and nanobiotechnology due to their excellent photo stability characteristics. In this paper, we reported stable, nontoxic and red fluorescent emission BSA-Au NCs for selective detection of L-dopamine (DA) in cerebrospinal fluid (CSF). The evolution was probed by various instrumental techniques such as UV-vis spectroscopy, High resolution transmission electron microscopy (HTEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), photoluminescence spectroscopy (PL). The synthesised BSA-Au NCs were showing 4–6 nm with high fluorescent ~8% Quantum yield (QY). The fluorescence intensity of BSA-Au NCs was quenched upon the addition of various concentrations of DA via an electron transfer mechanism. The decrease in BSA-Au NCs fluorescence intensity made it possible to determine DA in PBS buffer and the spiked DA in CSF in the linear range from 0 to 10 nM with the limit of detection (LOD) 0.622 and 0.830 nM respectively. Best of our knowledge, as-prepared BSA-Au NCs will gain possible strategy and good platform for biosensor, drug discovery, and rapid disease diagnosis such as Parkinson’s and Alzheimer diseases.

Graphene oxide functionalized with silver@silica-polyethylene glycol hybrid nanoparticles for direct electrochemical detection of quercetin.

A direct electrochemical detection of quercetin based on functionalized graphene oxide modified on gold-printed circuit board chip was demonstrated in this study. Functionalized graphene oxide materials are prepared by the covalent reaction of graphene oxide with silver@silica-polyethylene glycol nanoparticles (~12.35nm). Functionalized graphene oxide electrode shows a well-defined voltammetric response in phosphate buffered saline and catalyzes the oxidation of quercetin to quinone without the need of an enzyme. Significantly, the functionalized graphene oxide modified electrode exhibited a higher sensitivity than pristine gold-printed circuit board and graphene oxide electrodes, a wide concentration range of 7.5 to 1040nM and detection limit of 3.57nM. Developed biosensor platform is selective toward quercetin in the presence of an interferent molecule.

Surface activation of graphene oxide nanosheets by ultraviolet irradiation for highly efficient anti-bacterials

A comprehensive investigation of anti-bacterial properties of graphene oxide (GO) and ultraviolet (UV) irradiated GO nanosheets was carried out. Microscopic characterization revealed that the GO nanosheet-like structures had wavy features and wrinkles or thin grooves. Fundamental surface chemical states of GO nanosheets (before and after UV irradiation) were investigated using x-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. Minimum inhibitory concentration (MIC) results revealed that UV irradiated GO nanosheets have more pronounced anti-bacterial behavior than GO nanosheets and standard antibiotic, kanamycin. The MIC of UV irradiated GO nanosheets was 0.125 μg ml⁻¹ for Escherichia coli and Salmonella typhimurium, 0.25 μg ml⁻¹ for Bacillus subtilis and 0.5 μg ml⁻¹ for Enterococcus faecalis, ensuring its potential as an anti-infective agent for controlling the growth of pathogenic bacteria. The minimum bactericidal concentration of normal GO nanosheets was determined to be two-fold higher than its corresponding MIC value, indicating promising bactericidal activity. The mechanism of anti-bacterial action was evaluated by measuring the enzymatic activity of β-D-galactosidase for the hydrolysis of o-nitrophenol-β-D-galactopyranoside.

New function of molybdenum trioxide nanoplates: Toxicity towards pathogenic bacteria through membrane stress

Inorganic nanostructures are highly recognized for their potential use in the development of new functional materials for biomedical applications. In this study, we investigated the antibacterial efficiency of molybdenum trioxide (MoO3) nanoplates against four types of pathogenic bacteria. MoO3 nanoplates are synthesized by a simple wet chemical approach. X-ray diffraction and FT-IR analysis showed the presence of an orthorhombic phase of MoO3 nanoplates. Field emission scanning electron microscope studies confirmed the formation of plate-like structures of MoO3. The minimum inhibitory concentration (MIC) of MoO3 nanoplates against pathogenic bacteria was evaluated using a microdilution method. MICs such as 8μg/mL (against Escherichia coli and Salmonella typhimurium), 16μg/mL (against Enterococcus faecalis), and 8μg/mL (against Bacillus subtilis) show that MoO3 nanoplates have predominant antibacterial activity compared to the standard antibiotic, kanamycin. Evaluation of bacterial enzymatic (β-d-galactosidase) activity in the hydrolysis of o-nitrophenol and β-d-galactopyranoside suggested the disruption of the bacterial cell wall mechanism responsible for bacterial toxicity.

Osteogenic/Angiogenic Dual Growth Factor Delivery Microcapsules for Regeneration of Vascularized Bone Tissue

Growth factors (GFs) are major biochemical cues for tissue regeneration. Herein, a novel dual GF delivery system is designed composed of poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) and alginate microcapsules (MCs) via an electrodropping method. While bone morphogenetic protein (BMP)-2 is encapsulated in the PLGA NPs, vascular endothelial growth factor (VEGF) is included in the alginate MCs, where BMP-2-loaded PLGA NPs are entrapped together in the fabrication process. The initial loading efficiencies of BMP-2 and VEGF are 78% ± 3.6% and 43% ± 1.7%, respectively. When our dual GF-loaded MCs are assessed for in vitro osteogenesis of umbilical cord blood-derived mesenchymal stem cells (UCB-MSCs) on 2D and 3D environment, MCs contribute to much better UCB-MSCs osteogenesis as confirmed by von Kossa staining, immunofluorescence (osteocalcin, collagen 1), calcium content measurement, and osteogenic markers expression. In addition, when dual GF-encapsulated MCs are combined with collagen and then applied to 8 mm diameter rat calvarial defect model, the positive effects on vascularized bone regeneration are much more pronounced; micro computed tomography (CT) and histology analyses exhibit 82.3% bone healing coupled with 12.6% vessel occupied area. Put together, current study indicates a synergistic effect of BMP-2/VEGF and highlights the great potential of dual GF delivery modality (PLGA NPs-in-MC) for regeneration of vascularized bone.

Evaluation of cytotoxicity, biophysics and biomechanics of cells treated with functionalized hybrid nanomaterials

Hybrids consisting of carboxylated, single-walled carbon nanotube (c-SWNT)–silver nanoparticles (AgNPs)-DNA–poly vinyl alcohol (PVA) are synthesized via sequential functionalization to mimic the theragnostic (therapy and diagnosis) system. Carboxylation of SWNT has minimized the metal impurities with plenty of –COOH groups to produce hybrid (c-SWNT-AgNPs). The hybrid is further wrapped with DNA (hybrid-DNA) and encapsulated with PVA as hybrid composite (HC). Materials were tested against human alveolar epithelial cells (A549), mouse fibroblasts cells (NIH3T3) and human bone marrow stromal cells (HS-5). The composition-sensitive physico-chemical interactions, biophysics and biomechanics of materials-treated cells are evaluated. The cell viability was improved for HC, hybrid-PVA and c-SWNT when compared with SWNT and hybrid. SWNT and hybrid showed cell viability less than 60% at high dose (40 µg ml−1) and hybrid-PVA and HC retained 80% or more cell viability. The treatment of hybrid nanomaterials considerably changed cell morphology and intercellular interaction with respect to the composition of materials. Peculiarly, PVA-coated hybrid was found to minimize the growth of invadopodia of A549 cells, which is responsible for the proliferation of cancer cells. Surface roughness of cells increased after treatment with hybrid, where cytoplasmic regions specifically showed higher roughness. Nanoindentation results suggest that changes in biomechanics occurred owing to possible internalization of the hybrid. The changes in force spectra of treated cells indicated a possible greater interaction between the cells and hybrid with distinct stiffness and demonstrated the surface adherence and internalization of hybrid on or inside the cells.

Growth and restoration of a T-tile-based 1D DNA nanotrack

We designed an artificial one-dimensional DNA nanotrack that contains two T-motifs. It can be fabricated in a free solution and with a mica-assisted growth process. Also, we introduced a dry and wet method for the restoration of DNA nanostructures in order for them to be used in multiple applications.

Ultrasonochemically Conjugated Metalloid/Triblock Copolymer Nanocomposite and Subsequent Thin Solid Laminate Growth for Surface and Interface Studies

Polymer and metalloid nanoparticles can be conjugated in a symphonized manner using ultrasonochemical force to obtain hybrid nanocomposites. The process is demonstrated using polymer poly(ethylene glycol) (PEG), metalloid SiO(2)@Ag, and triblock copolymer ABA. The acoustic microstreaming and cavitation force from the ultrasonics are crucial parameters that determine the harmonized PEG stabilization and ABA blending of the metalloid nanocomposites that are obtained. Surface plasmon resonance in the resulting hybrid systems are examined by UV-vis absorbance spectroscopy. The resulting PEG-stabilized SiO(2)-Ag conjugated with a triblock copolymer poly(p-dioxanone-co-caprolactone)-block-poly(ethylene oxide)-block-poly(p-dioxanone-co-caprolactone) (PPDO-co-PCL-b-PEG-b-PPDO-co-PCL/ABA) (PEG-SiO(2)@Ag/ABA) shows a red shift of 20 nm (410 nm) from its initial resonance at 390 nm (PEG-SiO(2)@Ag). Nanocomposite particles were then spin-coated on a glass substrate to obtain the growth of thin solid laminates (thickness 27 microm). Structural functionality was studied by FT-IR, (1)H NMR, and FT-Raman spectroscopy. Morphological properties were ensured from FE-SEM, HRTEM, AFM, and FIB-SEM. Identity and crystallinity of the prepared nanocomposite were confirmed by XRD analysis. A very low weight percentile loss of the fabricated nanocomposites ensures its high thermal stability. Fabricated nanocomposite laminate might have a role in coating, reinforcement, and resistance and as substrate additives for a variety of surface and interface studies. Further, the ultrasonochemical approach utilized here could also be a smart system to fabricate other heteronanostructures in a single platform.

Synthesis of Silver Nanoclusters and Functionalization with Glucosamine for Glyconanoparticles

Functionalized nanoparticles are promising candidates for the construction of new nanomaterials. In this paper, glucosamine was covalently functionalized on the surface of silver nanoparticles to fabricate glyconanoparticles. Silver nanoclusters obtained by liquid-solid-solution (LSS) strategy under hydrothermal condition were first functionalized by carboxyl-terminated alkanethiol and the terminal carboxyl group was subsequently bonded with side-chain amino group of glucosamine surface through EDC/NHS coupling reaction. UV-vis spectrometer and EDXA measurements ensure the formation of silver nanoparticles. The surface functionalization of glucosamine on silver nanoparticles was confirmed from the carbonyl group of secondary amide linkage obtained by the conjugation of NHS terminated silver nanoparticles and amino group of glucosamine. This is evinced from the FT-IR characteristic stretching at 1637cm− 1 and 1H-NMR chemical shift from 8.4 to 7.6 ppm, respectively. Morphological images (FE-SEM and AFM) reveal the size and shape of the silver nano-assembly and silver-glucosamine nanoparticles. The fabricated glyconanoparticles with 15 ± 5 nm size can be easily suspended in water, stable over a broader range of pH and would be useful for variety of glyconanotechnology.