Hyung-Mo Kim

Facile method for preparation of silica coated monodisperse superparamagnetic microspheres

This paper presents a facile method for preparation of silica coated monodisperse superparamagnetic microsphere. Herein, monodisperse porous polystyrene-divinylbenzene microbeads were prepared by seeded emulsion polymerization and subsequently sulfonated with acetic acid/H2SO4. The as-prepared sulfonated macroporous beads were magnetized in presence of Fe2+/Fe3+ under alkaline condition and were subjected to silica coating by sol-gel process, providing water compatibility, easily modifiable surface form, and chemical stability. FE-SEM, TEM, FT-IR, and TGA were employed to characterize the silica coated monodisperse magnetic beads (∼7.5 µm). The proposed monodisperse magnetic beads can be used as mobile solid phase particles candidate for protein and DNA separation.

Double-Layer Magnetic Nanoparticle-Embedded Silica Particles for Efficient Bio-Separation

Superparamagnetic Fe3O4 nanoparticles (NPs) based nanomaterials have been exploited in various biotechnology fields including biomolecule separation. However, slow accumulation of Fe3O4 NPs by magnets may limit broad applications of Fe3O4 NP-based nanomaterials. In this study, we report fabrication of Fe3O4 NPs double-layered silica nanoparticles (DL MNPs) with a silica core and highly packed Fe3O4 NPs layers. The DL MNPs had a superparamagnetic property and efficient accumulation kinetics under an external magnetic field. Moreover, the magnetic field-exposed DL MNPs show quantitative accumulation, whereas Fe3O4 NPs single-layered silica nanoparticles (SL MNPs) and silica-coated Fe3O4 NPs produced a saturated plateau under full recovery of the NPs. DL MNPs are promising nanomaterials with great potential to separate and analyze biomolecules.

Carbon-doped freestanding TiO2 nanotube arrays in dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) were fabricated with both closed- and open-ended freestanding TiO2 nanotube arrays that were doped with carbon via chemical vapor deposition to improve their electron transport properties. The energy conversion efficiencies of DSSCs increased from 5.07% to 6.21% after doping with a small amount of carbon, i.e., an enhancement of 22.4%. This suggests that the π–π conjugation introduced by carbon doping improved the efficiency of electron transport. However, energy conversion efficiencies of DSSCs with a large amount of carbon doping on the TiO2 nanotube arrays decreased from 5.07% to 2.87%, with a lower short-circuit current, open circuit voltage, and fill factor because of the reduced level of dye adsorption on the TiO2 nanotube arrays.

Glucose detection using 4-mercaptophenyl boronic acid-incorporated silver nanoparticles-embedded silica-coated graphene oxide as a SERS substrate

In this work, 4-mercaptophenyl boronic acid (4-MPBA) was self-assembled on the surface of silver nanoparticle-embedded silica-coated graphene oxide (GO@SiO2@Ag NPs@MPBA) to detect glucose by surface enhanced Raman scattering (SERS). The SERS intensity of 4-MPBA on the GO@SiO2@Ag NPs was 2.2-fold greater than that of GO@Ag NPs. Moreover, silica-coated GO exhibited lower background signals compared to GO. The SERS intensity of GO@SiO2@Ag NPs@MPBA peaked at 1 mM 4-MPBA. pH-dependent behavior of 4-MPBA on the GO@SiO2 @Ag NPs was investigated; the highest SERS signal intensity was detected at pH 3. The binding of glucose to 4-MPBA-incorporated GO@SiO2@Ag NPs increased the SERS signals at both 1,072 and 1,588 cm-1. The linear range was estimated from 2 to 20 mM glucose. These results provide insight into detection of glucose and the development of SERS-based biosensors using graphene oxide.

β-CD Dimer-immobilized Ag Assembly Embedded Silica Nanoparticles for Sensitive Detection of Polycyclic Aromatic Hydrocarbons.

We designed a β-CD dimer on silver nanoparticles embedded with silica nanoparticles (Ag@SiO2 NPs) structure to detect polycyclic aromatic hydrocarbons (PAHs). Silica NPs were utilized as a template for embedding silver NPs to create hot spot structures and enhance the surface-enhanced Raman scattering (SERS) signal, and a thioether-bridged dimeric β-CD was immobilized on Ag NPs to capture PAHs. The assembled Ag NPs on silica NPs were confirmed by TEM and the presence of β-CD dimer on Ag@SiO2 was confirmed by UV-vis and attenuated total reflection-Fourier transform infrared spectroscopy. The β-CD dimer@Ag@SiO2 NPs were used as SERS substrate for detecting perylene, a PAH, directly and in a wide linearity range of 10−7 M to 10−2 M with a low detection limit of 10−8 M. Also, the β-CD dimer@Ag@SiO2 NPs exhibited 1000-fold greater sensitivity than Ag@SiO2 NPs in terms of their perylene detection limit. Furthermore, we demonstrated the possibility of detecting various PAH compounds using the β-CD dimer@Ag@SiO2 NPs as a multiplex detection tool. Various PAH compounds with the NPs exhibited their distinct SERS bands by the ratio of each PAHs. This approach of utilizing the assembled structure and the ligands to recognize target has potential for use in sensitive analytical sensors.

Preparation of plasmonic magnetic nanoparticles and their light scattering properties

Fe3O4@SiO2@Au nanoparticles (NPs) that have plasmonic and magnetic properties were prepared by simple immobilization method of Au NPs to silica coated magnetic NPs. The Fe3O4@SiO2@Au exhibit 5 times higher light scattering compared to the same sized gold NPs. The experimental results were supported by the simulations.

Highly sensitive and reliable SERS probes based on nanogap control of a Au–Ag alloy on silica nanoparticles

We developed highly sensitive surface-enhanced Raman scattering (SERS) probes based on SiO2@Au@Ag nanoparticles (NPs) using the Ag growth onto Au NP seeds method. The SiO2@Au@Ag NPs were synthesized by reducing Ag ions under mild conditions (ascorbic acid) and using the structure-directing agent polyvinylpyrrolidone (PVP). SERS activities of the NPs were tuned by adjusting AgNO3 concentration, resulting in the growth of the Ag shell on the surface of the Au NP seeds and the formation of narrow gaps between two Ag NPs on the surface of the probes. The NPs exhibited strong Raman signals originating from a highly enhanced E-field at the gaps. The SiO2@Au@Ag NPs exhibited a low limit of detection (LOD) value of 2.4 nM for ATP, which proves that they are highly sensitive probes. Moreover, reproducible Raman signals of the SiO2@Au@Ag NPs toward ATP were obtained in batch-to-batch experiments which is very promising for potential use in on-site detection.

Polyethylene Glycol-Engrafted Graphene Oxide as Biocompatible Materials for Peptide Nucleic Acid Delivery into Cells

Graphene oxide (GO) is known to strongly bind single-stranded nucleic acids with fluorescence quenching near the GO surface. However, GO exhibits weak biocompatibility characteristics, such as low dispersibility in cell culture media and significant cytotoxicity. To improve dispersibility in cell culture media and cell viability of GO, we prepared nanosized GO (nGO) constructs and modified the nGO surface using polyethylene glycol (PEG-nGO). Single-stranded peptide nucleic acid (PNA) was adsorbed onto the PEG-nGO and was readily desorbed by adding complementary RNA or under low pH conditions. PNA adsorbed on the PEG-nGO was efficiently delivered into lung cancer cells via endocytosis without affecting cell viability. Furthermore, antisense PNA delivered using PEG-nGO effectively downregulated the expression of the target gene in cancer cells. Our results suggest that PEG-nGO is a biocompatible carrier useful for PNA delivery into cells and serves as a promising gene delivery tool.

Silver Nanoparticle-Embedded Thin Silica-Coated Graphene Oxide as an SERS Substrate

A hybrid of Ag nanoparticle (NP)-embedded thin silica-coated graphene oxide (GO@SiO2@Ag NPs) was prepared as a surface-enhanced Raman scattering (SERS) substrate. A 6 nm layer of silica was successfully coated on the surface of GO by the physical adsorption of sodium silicate, followed by the hydrolysis of 3-mercaptopropyl trimethoxysilane. Ag NPs were introduced onto the thin silica-coated graphene oxide by the reduction of Ag+ to prepare GO@SiO2@Ag NPs. The GO@SiO2@Ag NPs exhibited a 1.8-fold enhanced Raman signal compared to GO without a silica coating. The GO@SiO2@Ag NPs showed a detection limit of 4-mercaptobenzoic acid (4-MBA) at 0.74 μM.

Effects of soy sauce on physicochemical and textural properties of tumbled chicken breast

The objective of this study was to evaluate the effects of soy sauce on the physicochemical and textural properties of tumbled chicken breasts. Chicken breasts marinated with distilled water (Con), 4% NaCl solution, 4% NaCl and lactic acid solution (pH 4.9), and soy sauce solution (4% salt concentration and pH 4.9) were vacuum tumbled at 3°C for 60 min. The chicken breast marinated with soy sauce solution showed lower lightness and higher redness and yellowness due to the color of the soy sauce. The acidic marinades led to a decrease in pH value of tumbled chicken breast. The acidic marinades increased collagen solubility of sample compared with 4% NaCl solution, resulting in decreased shear force. Water-holding capacity, marination and cooking yields, and solubility of myofibrillar proteins were mainly affected by the presence of salt in the marinade, rather than by pH alternation. Our results suggested that soy sauce marination can improve the tenderness of tumbled chicken breast.