Hyun Kyong Shon

One-step modification of superhydrophobic surfaces by a mussel-inspired polymer coating.

A bio-inspired approach for superhydrophobic surface modification was investigated. Hydrophilic conversion of the superhydrophobic surface was easily achieved through this method, and the superhydrophobic-hydrophilic alternating surface was generated by the method combined with soft-lithography. The resulting patterned surface showed high water adhesion property in addition to superhydrophobic property.

Microscale mechanisms of agarose-induced disruption of collagen remodeling

Cells are strongly influenced by the local structure and mechanics of the extracellular matrix (ECM). We recently showed that adding agarose to soft collagen ECMs can mechanically stiffen these hydrogels by two orders of magnitude while limiting 3D cell motility, which we speculated might derive from agarose-mediated inhibition of collagen fiber deformation and remodeling. Here, we directly address this hypothesis by investigating the effects of agarose on cell-collagen interactions at the microscale. Addition of agarose progressively restricts cell spreading, reduces stress fiber and focal adhesion assembly, and inhibits macroscopic gel compaction. While time-of-flight secondary ion mass spectrometry and scanning electron microscopy fail to reveal agarose-induced alterations in collagen ligand presentation, the latter modality shows that agarose strongly impairs cell-directed assembly of large collagen bundles. Agarose-mediated inhibition of cell spreading and cytoarchitecture can be rescued by β-agarase digestion or by covalently crosslinking the matrix with glutaraldehyde. Based on these results, we argue that cell spreading and motility on collagen requires local matrix stiffening, which can be achieved via cell-mediated fiber remodeling or by chemically crosslinking the fibers. These findings provide new mechanistic insights into the regulatory function of agarose and bear general implications for cell adhesion and motility in fibrous ECMs.

Bioinspired, Cytocompatible Mineralization of Silica–Titania Composites: Thermoprotective Nanoshell Formation for Individual Chlorella Cells†

Hard-shell case: Using a (RKK)4 D8 peptide allows mineralization to occur under cytocompatible conditions. Thus individual Chlorella cells could be encapsulated within a SiO2 -TiO2 nanoshell with high cell viability (87 %). The encapsulated Chlorella showed an almost threefold increase in their thermo-tolerance after 2 h at 45 °C.

Probing nanoparticles and nanoparticle-conjugated biomolecules using time-of-flight secondary ion mass spectrometry

Bio-conjugated nanoparticles have emerged as novel molecular probes in nano-biotechnology and nanomedicine and chemical analyses of their surfaces have become challenges. The time-of-flight (TOF) secondary ion mass spectrometry (SIMS) has been one of the most powerful surface characterization techniques for both nanoparticles and biomolecules. When combined with various nanoparticle-based signal enhancing strategies, TOF-SIMS can probe the functionalization of nanoparticles as well as their locations and interactions in biological systems. Especially, nanoparticle-based SIMS is an attractive approach for label-free drug screening because signal-enhancing nanoparticles can be designed to directly measure the enzyme activity. The chemical-specific imaging analysis using SIMS is also well suited to screen nanoparticles and nanoparticle-biomolecule conjugates in complex environments. This review presents some recent applications of nanoparticle-based TOF-SIMS to the chemical analysis of complex biological systems.

Surface characterization of plasma-polymerized cyclohexane thin film

A plasma-polymerized cyclohexane (PPCHex) thin film was characterized by using Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry along with a principal component analysis (PCA). The PPCHex thin film was deposited onto a silicon substrate by using an inductively coupled plasma chemical vapor deposition method and cyclohexane as a precursor. The chemical composition of the PPCHex surface was controlled in a reproducible manner as a function of substrate bias plasma power. A PCA of the TOF-SIMS data also gave systematic insight into the surface chemical compositions and molecular cross-linking on plasma-polymerized thin films as a function of substrate bias plasma power. PPCHex thin film made at 100W plasma power had the least amount of oxygen functional groups such as the C–O–H form on the surface than the one made at 10W plasma power.

Time-of-flight secondary ion mass spectrometry chemical imaging analysis of micropatterns of streptavidin and cells without labeling

A bismuth cluster ion-beam-based time-of-flight secondary ion mass spectrometry (TOF-SIMS) has been successfully used to image micropatterns of streptavidin and Chinese hamster ovary (CHO-k1) cells, as received and without any labeling. Three different analysis ion beams (Bi+, Bi3+, and Bi32+) were compared to obtain label-free TOF-SIMS chemical images of micropatterns of streptavidin, which were subsequently used for generating biotinylated cell patterns. Unlike using a Bi+ ion beam, using a Bi3+ or Bi32+ primary analysis ion beam yielded well-contrasted-TOF-SIMS images of streptavidin characteristic secondary ions. A principal component analysis of TOF-SIMS data was performed to generate a chemical image of the streptavidin itself. A chemical specific TOF-SIMS image analysis gave us a better understanding of the localization of cells at the outer boundaries of the streptavidin-patterned circles. Our work suggests that using cluster-ion analysis beams together with multivariate data analysis for TOF-SIMS...

Improved mass resolution and mass accuracy in TOF-SIMS spectra and images using argon gas cluster ion beams

The popularity of argon gas cluster ion beams (Ar-GCIB) as primary ion beams in time-of-flight secondary ion mass spectrometry (TOF-SIMS) has increased because the molecular ions of large organic- and biomolecules can be detected with less damage to the sample surfaces. However, Ar-GCIB is limited by poor mass resolution as well as poor mass accuracy. The inferior quality of the mass resolution in a TOF-SIMS spectrum obtained by using Ar-GCIB compared to the one obtained by a bismuth liquid metal cluster ion beam and others makes it difficult to identify unknown peaks because of the mass interference from the neighboring peaks. However, in this study, the authors demonstrate improved mass resolution in TOF-SIMS using Ar-GCIB through the delayed extraction of secondary ions, a method typically used in TOF mass spectrometry to increase mass resolution. As for poor mass accuracy, although mass calibration using internal peaks with low mass such as hydrogen and carbon is a common approach in TOF-SIMS, it is unsuited to the present study because of the disappearance of the low-mass peaks in the delayed extraction mode. To resolve this issue, external mass calibration, another regularly used method in TOF-MS, was adapted to enhance mass accuracy in the spectrum and image generated by TOF-SIMS using Ar-GCIB in the delayed extraction mode. By producing spectra analyses of a peptide mixture and bovine serum albumin protein digested with trypsin, along with image analyses of rat brain samples, the authors demonstrate for the first time the enhancement of mass resolution and mass accuracy for the purpose of analyzing large biomolecules in TOF-SIMS using Ar-GCIB through the use of delayed extraction and external mass calibration.

Electrochemical Release of Amine Molecules from Carbamate-Based, Electroactive Self-Assembled Monolayers

In this paper, carbamate-based self-assembled monolayers (SAMs) of alkanethiolates on gold were suggested as a versatile platform for release of amine-bearing molecules in response to the electrical signal. The designed SAMs underwent the electrochemical oxidation on the gold surface with simultaneous release of the amine molecules. The synthesis of the thiol compounds was achieved by coupling isocyanate-containing compounds with hydroquinone. The electroactive thiol was mixed with 11-mercaptoundecanol [HS(CH(2))(11)OH] to form a mixed monolayer, and cyclic votammetry was used for the characterization of the release behaviors. The mixed SAMs showed a first oxidation peak at +540 mV (versus Ag/AgCl reference electrode), indicating the irreversible conversion from carbamate to hydroquinone groups with simultaneous release of the amine molecules. The analysis of ToF-SIMS further indicated that the electrochemical reaction on the gold surface successfully released amine molecules.

TOF-SIMS analysis of an isocitrate dehydrogenase 1 mutation-associated oncometabolite in cancer cells

The development of analytical tools for accurate and sensitive detection of intracellular metabolites associated with mutated metabolic enzymes is important in cancer diagnosis and staging. The gene encoding the metabolic enzyme isocitrate dehydrogenase 1 (IDH1) is mutated in various cancers, and mutant IDH1 could represent a good biomarker and potent target for cancer therapy. Owing to a mutation in an important arginine residue in the catalytic pocket, mutant IDH1 catalyzes the production of 2-hydroxyglutarate (2-HG) instead of its wild type product α-ketoglutarate (α-KG), which is involved in multiple cellular pathways involving the hydroxylation of proteins, ribonucleic acid, and deoxyribose nucleic acid (DNA). Since 2-HG is an α-KG antagonist, inhibiting normal α-KG-dependent metabolism, high intracellular levels of 2-HG result in abnormal histone and DNA methylation. Therefore, accurate and sensitive analytical tools for the direct detection of 2-HG in cancer cells expressing mutant IDH1 would benefit this field, as it would minimize the need both for complicated experimental procedures and for large amounts of biological samples. Here, the authors describe a useful analytical method for the direct detection of 2-HG in lysates from a mutant IDH1-expressing cell line by time-of-flight secondary ion mass spectrometry (TOF-SIMS) analysis, a powerful surface analysis tool. In addition, the authors verified the efficacy of the specific mutant IDH1 inhibitor AGI-5198 by tracking the intracellular 2-HG concentration, which decreased in a dose-dependent manner. Our results demonstrate the large potential of TOF-SIMS as an analytical tool for the simple, direct detection of oncometabolites during cancer diagnosis, and for verifying the efficiency of the targeted cancer drugs.

Molecular depth profiling on rat brain tissue sections prepared using different sampling methods

Brain imaging using time-of-flight secondary ion mass spectrometry (ToF-SIMS) has been reported to produce the distorted biomolecular distributions due to the cholesterol-induced matrix effect when cholesterol migrates to the surface, particularly in white matter, which contains a high level of cholesterol. Frozen-hydrated analysis has been used to inhibit the movement of cholesterol in the brain. In this paper, the authors propose new sample preparation and drying methods that can be used to obtain accurate biomolecular images at room temperature, instead of frozen-hydrated analysis using liquid-nitrogen, which must be continuously supplied to maintain the sample at -160 °C during the experiment. The rat brain prepared by the tape-supporting method on a precooled (-20 °C) stainless steel plate was freeze-dried in a load-lock chamber of ToF-SIMS for about an hour and moved directly to the main chamber. Using this preparation method, the authors found that cholesterol did not migrate to the surface in the corpus callosum (white matter) of the rat brain and sulfatide-related signals obtained from the cerebellum were not reduced in white matter. Our tape-supporting and freeze-drying sampling method for brain tissues could be a useful tool to study important metabolites of neurodegenerative diseases.