Homan Kang

Multifunctional Silver‐Embedded Magnetic Nanoparticles as SERS Nanoprobes and Their Applications

In this study, surface-enhanced Raman spectroscopy (SERS)-encoded magnetic nanoparticles (NPs) are prepared and utilized as a multifunctional tagging material for cancer-cell targeting and separation. First, silver-embedded magnetic NPs are prepared, composed of an 18-nm magnetic core and a 16-nm-thick silica shell with silver NPs formed on the surface. After simple aromatic compounds are adsorbed on the silver-embedded magnetic NPs, they are coated with silica to provide them with chemical and physical stability. The resulting silica-encapsulated magnetic NPs (M-SERS dots) produce strong SERS signals and have magnetic properties. In a model application as a tagging material, the M-SERS dots are successfully utilized for targeting breast-cancer cells (SKBR3) and floating leukemia cells (SP2/O). The targeted cancer cells can be easily separated from the untargeted cells using an external magnetic field. The separated targeted cancer cells exhibit a Raman signal originating from the M-SERS dots. This system proves to be an efficient tool for separating targeted cells. Additionally, the magnetic-field-induced hot spots, which can provide a 1000-times-stronger SERS intensity due to aggregation of the NPs, are studied.

Macroporous Polystyrene-Supported Palladium Catalyst Containing a Bulky N-Heterocyclic Carbene Ligand for Suzuki Reaction of Aryl Chlorides

Macroporous polystyrene (MPS)-supported 1-mesitylimidazolium chloride resin was prepared by reacting macroporous chloromethyl polystyrene with 1-mesitylimidazole as a supported N-heterocyclic carbene (NHC) precursor for the immobilization of a palladium catalyst. This MPS-supported NHC precursor readily formed a stable complex with Pd(OAc)2, which effectively catalyzed the Suzuki reaction of aryl iodide and bromides at room temperature and even aryl chlorides at elevated temperatures (100 degrees C). This catalyst showed reusability in the Suzuki reaction of aryl bromide.

Surface-enhanced Raman scattering-active nanostructures and strategies for bioassays

Surface-enhanced Raman scattering (SERS) techniques offer a number of advantages in molecular detection and analysis, particularly in terms of the multiplex detection of biomolecules. So far, many new SERS-based substrates and analytical techniques have been reported. For easy understanding, various SERS techniques are classified into the following four categories: adsorption-mediated direct detection; antibody- or ligand-mediated direct detection; binding catalyzed indirect detection; and tag-based indirect detection. Among these, recent successes of SERS tagging/encoding (nano/micro) materials and detection methods are highlighted, including our recent works. Some novel SERS-based strategies for the detection of several biological molecules are also introduced.

Single-step and rapid growth of silver nanoshells as SERS-active nanostructures for label-free detection of pesticides.

We explored a single-step approach for the rapid growth of Ag nanoshells (Ag NSs) under mild conditions. Without predeposition of seed metals, a uniform and complete layer of Ag shells was rapidly formed on silica core particles within 2 min at 25 °C via single electron transfer from octylamine to Ag(+) ions. The size and thickness of the Ag NSs were effectively tuned by adjusting the concentration of silica nanoparticles (silica NPs) with optimal concentrations of AgNO3 and octylamine. This unusually rapid growth of Ag NSs was attributed to a significant increase in the reduction potential of the Ag(+) ions in ethylene glycol (EG) through the formation of an Ag/EG complex, which in turn led to their facile reduction by octylamine, even at room temperature. A substantial enhancement in the surface-enhanced Raman scattering (SERS) of the prepared Ag NSs was demonstrated. The Ag NSs were also utilized as SERS-active nanostructures for label-free detection of the pesticide thiram. The Ag NS-based SERS approach successfully detected thiram on apple peel down to the level of 38 ng/cm(2) in a label-free manner, which is very promising with respect to its potential use for the on-site detection of residual pesticides.

Protein separation and identification using magnetic beads encoded with surface-enhanced Raman spectroscopy

This article presents a prototype of a surface-enhanced Raman spectroscopy (SERS)-encoded magnetic bead of 8mum diameter. The core part of the bead is composed of a magnetic nanoparticle (NP)-embedded sulfonated polystyrene bead. The outer part of the bead is embedded with Ag NPs on which labeling molecules generating specific SERS bands are adsorbed. A silica shell is fabricated for further bioconjugation and protection of SERS signaling. Benzenethiol, 4-mercaptotoluene, 2-naphthalenethiol, and 4-aminothiophenol are used as labeling molecules. The magnetic SERS beads are used as substrates for protein sensing and screening with easy handling. As a model application, streptavidin-bound magnetic SERS beads are used to illustrate selective separation in a flow cytometry system, and the screened beads are spectrally recognized by Raman spectroscopy. The proposed magnetic SERS beads are likely to be used as a versatile solid support for protein sensing and screening in multiple assay technology.

Magnetic surface-enhanced Raman spectroscopic (M-SERS) dots for the identification of bronchioalveolar stem cells in normal and lung cancer mice

Bronchioalveolar stem cells (BASCs) play an important role in the development of cancer. To study the characterization of BASCs, their isolation and purification are important. However, the cells are very rare in tissues and the available methods of isolating them are limited. The current study was performed to isolate BASCs in the murine lung using magnetic nanoparticle-based surface-enhanced Raman spectroscopic dots (M-SERS Dots). We used K-ras(LA1) mice, a laboratory animal model of non-small cell lung cancer of human, and C57BL/6 mice having the same age as a control. We compared the BASCs between 2 species by FACS analysis with 4 markers of BASCs, CCSP, SP-C, CD34, and Sca-1. We found that BASCs were more abundant in the K-ras(LA1) mice than in the C57BL/6 mice. Also, the M-SERS Dot-mediated positive selection of the CD34(pos) cells enabled the BASCs to be enriched to an approximately 4- to 5-fold higher level than that in the case without pre-separation. In summary, our study demonstrates the potential of using M-SERS Dots as a sorting system with very effective isolation of BASCs and multiplex targeting probe, showing that they may play an effective role in the study of BASCs in the future.

Fluorescence-Based Multiplex Protein Detection Using Optically Encoded Microbeads

Potential utilization of proteins for early detection and diagnosis of various diseases has drawn considerable interest in the development of protein-based multiplex detection techniques. Among the various techniques for high-throughput protein screening, optically-encoded beads combined with fluorescence-based target monitoring have great advantages over the planar array-based multiplexing assays. This review discusses recent developments of analytical methods of screening protein molecules on microbead-based platforms. These include various strategies such as barcoded microbeads, molecular beacon-based techniques, and surface-enhanced Raman scattering-based techniques. Their applications for label-free protein detection are also addressed. Especially, the optically-encoded beads such as multilayer fluorescence beads and SERS-encoded beads are successful for generating a large number of coding.

Target-specific near-IR induced drug release and photothermal therapy with accumulated Au/Ag hollow nanoshells on pulmonary cancer cell membranes.

Au/Ag hollow nanoshells (AuHNSs) were developed as multifunctional therapeutic agents for effective, targeted, photothermally induced drug delivery under near-infrared (NIR) light. AuHNSs were synthesized by galvanic replacement reaction. We further conjugated antibodies against the epidermal growth factor receptor (EGFR) to the PEGylated AuHNS, followed by loading with the antitumor drug doxorubicin (AuHNS-EGFR-DOX) for lung cancer treatment. AuHNSs showed similar photothermal efficiency to gold nanorods under optimized NIR laser power. The targeting of AuHNS-EGFR-DOX was confirmed by light-scattering images of A549 cells, and doxorubicin release from the AuHNSs was evaluated under low pH and NIR-irradiated conditions. Multifunctional AuHNS-EGFR-DOX induced photothermal ablation of the targeted lung cancer cells and rapid doxorubicin release following irradiation with NIR laser. Furthermore, we evaluated the effectiveness of AuHNS-EGFR-DOX drug delivery by comparing two drug delivery methods: receptor-mediated endocytosis and cell-surface targeting. Accumulation of the AuHNS-EGFR-DOX on the cell surfaces by targeting EGFR turned out to be more effective for lung cancer treatments than uptake of AuHNS-EGFR-DOX. Taken together, our data suggest a new and optimal method of NIR-induced drug release via the accumulation of targeted AuHNS-EGFR-DOX on cancer cell membranes.

Fluorescence-Raman Dual Modal Endoscopic System for Multiplexed Molecular Diagnostics

Optical endoscopic imaging, which was recently equipped with bioluminescence, fluorescence, and Raman scattering, allows minimally invasive real-time detection of pathologies on the surface of hollow organs. To characterize pathologic lesions in a multiplexed way, we developed a dual modal fluorescence-Raman endomicroscopic system (FRES), which used fluorescence and surface-enhanced Raman scattering nanoprobes (F-SERS dots). Real-time, in vivo, and multiple target detection of a specific cancer was successful, based on the fast imaging capability of fluorescence signals and the multiplex capability of simultaneously detected SERS signals using an optical fiber bundle for intraoperative endoscopic system. Human epidermal growth factor receptor 2 (HER2) and epidermal growth factor receptor (EGFR) on the breast cancer xenografts in a mouse orthotopic model were successfully detected in a multiplexed way, illustrating the potential of FRES as a molecular diagnostic instrument that enables real-time tumor characterization of receptors during routine endoscopic procedures.

Ag Shell−Au Satellite Hetero-Nanostructure for Ultra-Sensitive, Reproducible, and Homogeneous NIR SERS Activity

It is critical to create isotropic hot spots in developing a reproducible, homogeneous, and ultrasensitive SERS probe. Here, an Ag shell-Au satellite (Ag-Au SS) nanostructure composed of an Ag shell and surrounding Au nanoparticles was developed as a near-IR active SERS probe. The heterometallic shell-satellite structure based SERS probe produced intense and uniform SERS signals (SERS enhancement factor ∼1.4 × 10(6) with 11% relative standard deviation) with high detectability (100% under current measurement condition) by 785 nm photoexcitation. This signal enhancement was independent of the laser polarizations, which reflects the isotropic feature of the SERS activity of Ag-Au SS from the three-dimensional (3D) distribution of SERS hot spots between the shell and the surrounding satellite particles. The Ag-Au SS nanostructure shows a great potential as a reproducible and quantifiable NIR SERS probe for in vivo targets.