Minsub Chung

A Simple and Fast Aqueous-Phase Synthesis of Ultra-Highly Concentrated Silver Nanoparticles and Their Catalytic Properties

A simple and fast synthetic route to ultra-highly concentrated silver nanoparticles with long-term stability by reducing AgNO3 with ascorbic acid in the presence of polyethyleneimine (PEI) as a stabilizer in an aqueous phase is reported. The concentration of silver precursor was as high as 2000 mm (200 g of Ag nanoparticle per liter of water) and the reaction time was less than 10 min. The resulting silver nanoparticles show long-term stability after two months of storage at room temperature without any signs of particle aggregation or precipitation in an aqueous phase. The successful ligand exchange of PEI-stabilized silver nanoparticles to polyethylene glycol (PEG) and polyvinylpyrrolidone (PVP) without particle aggregation is also demonstrated. In addition, the catalytic activities of silver nanoparticles stabilized by various stabilizers prepared by the ligand exchange method was investigated. The PEI-stabilized silver nanoparticles exhibited a higher stability than those of PEG- and PVP-stabilized silver nanoparticles in the diffusion-controlled catalytic reduction of 4-nitrophenol to 4-aminophenol by NaBH4 .

Microchamber Western Blotting Using Poly-l-Lysine Conjugated Polyacrylamide Gel for Blotting of Sodium Dodecyl Sulfate Coated Proteins

We report a novel strategy to immobilize sodium dodecyl sulfate (SDS)-coated proteins for fully integrated microfluidic Western blotting. Polyacrylamide gel copolymerized with a cationic polymer, poly-L-lysine, effectively immobilizes all sized proteins after sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), and enables SDS-PAGE and subsequent immuno-probing in an automated microfluidic chip. Design of a poly-l-lysine conjugated polyacrylamide gel allows optimization of SDS-protein immobilization strength in the blotting gel region of the microchamber. The dependence of protein capture behavior on both the concentration of copolymerized charges and poly-lysine length is studied and gives important insight into an electrostatic immobilization mechanism. Based on analysis of protein conformation, the immobilized proteins bind with partner antibody after SDS dilution. We demonstrate each step of the microchamber Western blot, including injection, separation, transfer, immobilization, blocking, and immunoblot. The approach advances microfluidic protein immunoblotting, which is directly relevant to the widely-used SDS-PAGE based slab-gel Western blot, while saving sample volume, labor, and assay time.

Influence of Vitreoscilla hemoglobin gene expression on 2,3-butanediol production in Klebsiella oxytoca

A hemoglobin-like protein is a protein that aids in the delivery of oxygen in microbes in a similar fashion as hemoglobins in plants and animals. In this study, expression of Vitreoscilla hemoglobin (VHb) was used to improve the growth of Klebsiella oxytoca, and consequently, the 2,3-butanediol (2,3-BDO) production. The Vitreoscilla hemoglobin gene (vgb) was cloned into the expression vector pET-24a, and the recombination plasmid was then transformed in Klebsiella oxytoca ATCC43863. The efficiency of 2,3-BDO production and cell growth was analyzed by placing VHb expression under the control of the nar and luxS promoters instead of the T7 in Klebsiella oxytoca. Fermentation experiments were performed for comparison with the wild type under conditions of high/low aeration for the optimization of VHb-expressing cells in a 500 mL shaking flask and a 5 L fermenter. Moreover, cultivations were performed with addition of acetic acid to the culture media to study the effects of acetic acid on 2,3-BDO production, as acetic acid is known to induce 2,3-BDO production. The results indicated a 10% increase of cell growth in the presence of VHb, while 2,3-BDO production was further improved by the addition of acetic acid. In particular, the fed-batch fermentation of Klebsiella oxytoca LV with acetic acid added exhibited increase of the dry cell weight from 11.9 to 14.0 g/L, and improvement of the 2,3-BDO production from 34.9 to 49.4 g/L in 40 h.

Influence of natural organic matter (NOM) coatings on nanoparticle adsorption onto supported lipid bilayers

As the worldwide usage of nanoparticles in commercial products continues to increase, there is growing concern about the environmental risks that nanoparticles pose to biological systems, including potential damage to cellular membranes. A detailed understanding of how different types of nanoparticles behave in environmentally relevant conditions is imperative for predicting and mitigating potential membrane-associated toxicities. Herein, we investigated the adsorption of two popular nanoparticles (silver and buckminsterfullerene) onto biomimetic supported lipid bilayers of varying membrane charge (positive and negative). The quartz crystal microbalance-dissipation (QCM-D) measurement technique was employed to track the adsorption kinetics. Particular attention was focused on understanding how natural organic matter (NOM) coatings affect nanoparticle-bilayer interactions. Both types of nanoparticles preferentially adsorbed onto the positively charged bilayers, although NOM coatings on the nanoparticle and lipid bilayer surfaces could either inhibit or promote adsorption in certain electrolyte conditions. While past findings showed that NOM coatings inhibit membrane adhesion, our findings demonstrate that the effects of NOM coatings are more nuanced depending on the type of nanoparticle and electrolyte condition. Taken together, the results demonstrate that NOM coatings can modulate the lipid membrane interactions of various nanoparticles, suggesting a possible way to improve the environmental safety of nanoparticles.

Synthesis and characterization of an ELP-conjugated liposome with thermo-sensitivity for controlled release of a drug

Liposome, one of various drug carriers, has been extensively studied as an inert carrier for the delivery of protein, DNA, and biologically active agents into cells. Recently, much effort has been directed to the development of stimuli-sensitive liposomes that are able to respond to certain internal or external stimuli, such as, pH, electricity, temperature, magnet, or light. Among them, to obtain liposomes which release the contents in response to ambient temperature, liposomes have been modified with chemically synthetic polymers having various lower critical solution temperatures (LCST). In this study, instead of chemically synthetic polymers, a biologically produced elastin-like polypeptide (ELP), which was composed of oligomeric repeats of the pentapeptide sequence (Val-Pro-Gly-Val- Gly), was used for endowing the liposome with thermosensitivity. A model drug was encapsulated in the ELPconjugated liposomes and the release behavior of the drug caused by the liposome disruption due to the aggregation of ELPs was investigated. In addition, conjugation of ELP to liposome was identified with Fourier Transformed Infrared (FT-IR) and Scanning Electron Microscope (SEM) analyses.

Single amino acid replacement transforms mCherry to a far-red fluorescent protein

Far-red fluorescent proteins are beneficial for imaging in mammals. Here, starting from mCherry, the most commonly used among the different types of red fluorescent proteins (RFP), not having a H-bond network in its original form, we sought to recover the hydrogen bond network in mCherry. By comparing the structure of wtGFP and mCherry, we focused on a few key residues involved in a proton wire, and discovered an I197T mutant that showed a more red-shifted fluorescence. The detailed optical and photo-switching properties of related engineered RFPs are described. This study will guide further development of monomeric far-red FPs.

Note: A microfluidic freezer based on evaporative cooling of atomized aqueous microdroplets

We report for the first time water-based evaporative cooling integrated into a microfluidic chip for temperature control and freezing of biological solution. We opt for water as a nontoxic, effective refrigerant. Aqueous solutions are atomized in our device and evaporation of microdroplets under vacuum removes heat effectively. We achieve rapid cooling (-5.1 °C/s) and a low freezing temperature (-14.1 °C). Using this approach, we demonstrate freezing of deionized water and protein solution. Our simple, yet effective cooling device may improve many microfluidic applications currently relying on external power-hungry instruments for cooling and freezing.

Effect of polymerization conditions on the size change of poly(ethylene glycol) hydrogel nanoparticles

Suspension polymerization was used to prepare PEG homopolymer particles with nanometer size. In order to achieve the optimized reaction conditions for producing the smallest nanosized particles, the effects of various reaction conditions such as sonication, monomer concentration, molecular weight of monomer, and stabilizer concentration on the size of PEG hydrogel nanoparticles were investigated. Among these reaction conditions, sonication and the molecular weight of the monomer affected significantly the size reduction of PEG hydrogel nanoparticles, that is, the particle size decreased as sonication was conducted and the molecular weight of the monomer decreased. PEG homopolymer hydrogel nanoparticles having an average size of 182.1 nm were finally obtained with optimized reaction conditions.