Search

Cerium dioxide nanoparticles (CeONPs) have been extensively applied in research for future energy development due to two common oxidation states on their surface. Considering that shape (aspect ratio) is a key determinant of NPs-induced toxicity, we compared the toxicity of hexagonal (H)- and rod-shaped (R)-CeONPs in mice. At 24h after pharyngeal aspiration, both types of CeONPs recruited surrounding immune cells (monocytes and neutrophils) into the lung, and R-CeONPs induced a more severe pulmonary inflammatory response compared with H-CeONPs. To identify an indicator to predict pulmonary inflammatory responses at the cellular level, we also investigated their responses in alveolar macrophage cells. At 24h after treatment, both types of CeONPs were mainly located within the vacuoles (partially, in the lysosome) in the cytoplasm. Mitochondrial damage, intracellular calcium accumulation, and increased NO production were observed in cells exposed to both types of CeONPs, ultimately resulting in a decrease in cell viability. More interestingly, both types of CeONPs formed multinucleated giant cells. Meanwhile, contrary to when suspended in deionized water, R-CeONPs were strongly aggregated with a negative charge in cell culture media, whereas H-CeONPs were relatively well-dispersed with a positive charge. R-CeONPs-induced lysosomal extension was also recovered by premix with negatively charged DNA, and even NPs suspended in cell culture media without cells were detected under the FACS system, suggesting interference by protein corona. Therefore, we suggest that shape (aspect ratio) is an important factor determining inhaled NPs-induced pathology and that the effect of the surface charge and protein corona should be carefully considered in interpreting results derived from in vitro tests. Furthermore, we propose that the relationship between the formation of multinucleated giant cells and the inflammatory response of inhaled CeONPs should be further studied.

Appropriate surface designs and precise characterizations of nanoparticles (NPs) are important but as of yet unrealized in biomedical applications of nanomaterials. We report a facile synthetic approach to the preparation of iron oxide (Fe3O4) NPs with different surface charges through exchange with polymeric ligands. An accurate analysis method for characterization of the surface-modified Fe3O4 NPs using a combination of the time-of-flight secondary ion mass spectrometry (ToF-SIMS) and Fourier transform infrared spectroscopy (FT-IR) techniques is demonstrated. A comparison of the spatial distribution of the ligand and core particles with ToF-SIMS and FT-IR verified the successful modification and purification. In addition, the surface was shown to play an important role in interactions with live cells in terms of cytotoxicity, cellular uptake, and even gene transfection. Interestingly, precise control over the surface chemistry of NP enabled efficient transfection of siRNA into suspension type cell, the Jurkat human leukemic T cell line, achieving successful down regulation of NOTCH1 whose signaling pathway is known to be involved in acute leukemia. Our report presents an in-depth study of the interactions between the NPs and cells, as well as their synthesis, characterization, and surface-dependent performance properties.

We report polyethylene glycol (PEG)-grafting antifouling surfaces using a plasma copolymerized (PcP) technique to monitor protease activity in complex media. By varying the mixing ratio of the PEG and ethylenediamine (EDA) precursors, the PcP-PEG-EDA (PcP-PE) film was able to easily control surface amine density with good preservation of the internal PEG structure. We found that nonspecific protein adsorption was dramatically reduced in serum-containing media on the PcP-PE films, as opposed to that on plasma polymerized-EDA (PP-E) films without PEG. When SPR sensor chips coated with PcP-PE film were employed to detect protease activity, biotinylated luciferase probes (luciferase-peptide-biotin) on streptavidin-conjugated SPR chips enabled real-time and label-free measurement of matrix metalloproteinase activity in cell culture media. Owing to its excellent antifouling ability, this newly developed method boasts minimal nonspecific binding and can serve as a biochip platform to promote a wide range of applications in the biological field.

In recent years, many methods have been investigated to improve imaging speed in photoacoustic microscopy (PAM). These methods mainly focused upon three critical factors contributing to fast PAM: laser pulse repetition rate, scanning speed, and computing power of the microprocessors. A high laser repetition rate is fundamentally the most crucial factor to increase the PAM speed. In this paper, we review methods adopted for fast PAM systems in detail, specifically with respect to light sources. To the best of our knowledge, ours is the first review article analyzing the fundamental requirements for developing high-speed PAM and their limitations from the perspective of light sources.

We have studied the origin of degradation in solution-processed organic light-emitting diodes (s-OLEDs) by using X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (TOF-SIMS) depth profiling. Successful mechanical exfoliation of top cathode layers from degraded s-OLEDs and Ar gas cluster ion beam sputtering of remaining organic layer stack enabled us to probe chemical and positional changes at the relevant buried interfaces in the degraded device. Our XPS depth profile data showed that device operation induced migration of PEDOT in PEDOT:PSS layer toward the interface between hole transport layer (HTL) and emissive layer (EML), which lowers the hole injection efficiency and shifts the carrier recombination zone toward the interface. TOF-SIMS depth profile data showed that molecular decomposition occurred only in the EML after the device operation. These results depict a scenario in which migration of PEDOT lowers the hole injection efficiency which in turn shifts the recombination zone toward the mixed interface between HTL and EML, where an accumulation of excitons and hole polarons induces strong exciton-polaron quenching that results in molecular break down and device degradation.

Machine vision techniques for monitoring heart rates in aquatic bioassays have been applied to cardiotoxicity assessment. However, the requisite large data sizes and long calculation times make long-term observations of heart rates difficult. In this study, we developed a real-time heart rate monitoring system for individual Daphnia magna in a water chamber mounter that immobilizes their movement in 100 mL media. Heart rates are calculated from real-time, time-resolved relative phase information from digital holograms acquired with a 200 fps camera and parallel computation using a graphics processing unit. With this system, we monitored the real-time changes in the heart rates of individual D. magna specimens exposed to H2O2 as a positive control for reactive oxygen species (ROS) levels in an aquatic environment for 10 h, a period long enough to observe dynamic heart rate responses to the mounting process and exposure and to establish heart rate trends. An additional group analysis was conducted to compare to conventional cardiotoxicity assessment, with results of both assessments showing that the heart rates reduced according to ROS level by H2O2 exposure concentration. Notably, the results of our real-time dynamic heart rate monitoring in aquatic conditions indicated that establishing a relaxation heart rate before measurements could improve the accuracy of toxicity assessment. It is believed that the system developed in this study, achieving the simultaneous measurement, analysis, and display of reconstructed results, will find wide application in other aquatic bioassays.

MicroRNAs (miRNAs) are important post-transcriptional gene regulators and can serve as potential biomarkers for many diseases. Most of the current miRNA detection techniques require purification from biological samples, amplification, labeling, or tagging, which makes quantitative analysis of clinically relevant samples challenging. Here we present a new strategy for the detection of miRNAs with uniformity over a large area based on signal amplification using enzymatic reactions and measurements using time-of-flight secondary ion mass spectrometry (ToF-SIMS), a sensitive surface analysis tool. This technique has high sequence specificity through hybridization with a hairpin DNA probe and allows the identification of single-base mismatches that are difficult to distinguish by conventional mass spectrometry. We successfully detected target miRNAs in biological samples without purification, amplification, or labeling of target molecules. In addition, by adopting a well-known chromogenic enzymatic reaction from the field of biotechnology, we extended the use of enzyme-amplified signal enhancement ToF (EASE-ToF) to protein detection. Our strategy has advantages with respect to scope, quantification, and throughput over the currently available methods, and is amenable to multiplexing based on the outstanding molecular specificity of mass spectrometry (MS). Therefore, our technique not only has the potential for use in clinical diagnosis, but also provides evidence that MS can serve as a useful readout for biosensing to perform multiplexed analysis extending beyond the limitations of existing technology.

The direct in situ synthesis of cadmium sulfide (CdS) nanowires (NWs) was presented by direct synthesis of CdS NWs on the gold surface of an interdigitated electrode (IDE). In this work, we investigated the effect of a strong oxidant on the surfaces of the CdS NWs using X-ray photoelectron spectroscopy, transmission electron microscopy, and time-of-flight secondary ion mass spectrometry. We also fabricated a parylene-C film as a surface passivation layer for in situ-synthesized CdS NW photosensors and investigated the influence of the parylene-C passivation layer on the photoresponse during the coating of parylene-C under vacuum using a quartz crystal microbalance and a photoanalyzer. Finally, we used the in situ-synthesized CdS NW photosensor with the parylene-C passivation layer to detect the chemiluminescence of horseradish peroxidase and luminol and applied it to medical detection of carcinoembryonic antigen.

Nanoparticles adsorb biomolecules to form corona upon entering the biological environment. In this study, tissue-specific corona formation is provided as a way of controlling protein interaction with nanoparticles in vivo. In the vitreous, the composition of the corona was determined by the electrostatic and hydrophobic properties of the associated proteins, regardless of the material (gold and silica) or size (20- and 100-nm diameter) of the nanoparticles. To control protein adsorption, we pre-incubate 20-nm gold nanoparticles with 5 selectively enriched proteins from the corona, formed in the vitreous, to produce nanoparticle-protein complexes. Compared to bare nanoparticles, nanoparticle-protein complexes demonstrate improved binding to vascular endothelial growth factor (VEGF) in the vitreous. Furthermore, nanoparticle-protein complexes retain in vitro anti-angiogenic properties of bare nanoparticles. In particular, priming the nanoparticles (gold and silica) with tissue-specific corona proteins allows nanoparticle-protein complexes to exert better in vivo therapeutic effects by higher binding to VEGF than bare nanoparticles. These results suggest that controlled corona formation that mimics in vivo processes may be useful in the therapeutic use of nanomaterials in local environment.

Reduced graphene oxide (rGO) is a graphene-like material that exhibits high productivity for a wide range of industrial applications. To promote the application of rGO, it is important to not only produce high-quality rGO but also precisely evaluate the output. The intensity ratio of the D to G band in the Raman scattering is commonly used to assess the defect density of the carbon materials; however, this ratio is limited to evaluate the reduction degree of rGO because of the ambiguity arising from the superposition of the bands. In this study, we investigate the relationship between the intensity ratio of D* to G band and the reduction of graphene oxide (GO) to evaluate the degree of reduction of rGO. The spectral analysis of GO and rGO, along with systematic research of the thermally reduced GO synthesized via thermal treatment (100–900 °C) revealed a strong linkage between the D*/G intensity ratio and the C/O atomic ratio. The atomic vibrational relationships were elucidated by the assignment of the D* band, based on the density functional perturbation theory calculations. These findings explain the atomic vibrational properties of rGO and provide an indicator of the quality of rGO to optimize its performance for applications.

Fabrication methods to produce an amine-functionalized surface have been widely investigated as it is a promising substrate for biological studies, owing to its ability to stably immobilize various biomolecules. In this study, a biocompatible amine-functionalized polyethylene glycol (aPEG) thin film was fabricated by using plasma-enhanced chemical vapor deposition (PECVD) to overcome the disadvantages of the conventional wet process. A functionalized PEG diamine was used as a single precursor to simplify the fabrication process, and the relationship between the surface functional group density and the plasma power was investigated. Also, the surfaces of the functionalized thin films were quantitatively analyzed to determine the optimal fabrication condition that yields the most excellent surface amine density. The non-fouling resistance of the aPEG thin film and its applicability for biological applications was demonstrated by successfully immobilizing the matrix metalloproteinase-7 (MMP-7) enzyme, which is a well-known biomarker for cancers, with minimal non-specific adsorption (NSA). Our fabrication method was further applied to the modification of rather challenging substrates, including carbon paper, polyethylene terephthalate (PET) film, silicon wafer, polyvinylidene fluoride (PVDF), and successful modification was confirmed by the results of time-of-flight secondary ion mass spectrometry (ToF-SIMS) analysis. It is expected that our fabrication method can enable applications of the functionalized thin film in bioscience by presenting a versatile surface modification technique for deposition of biocompatible material onto various substrates, which can be potentially used in disease diagnosis, medical implants, and bioengineering.

In this work, an extracellular matrix permeability/efficacy assay tip (E-PAT), which can be used in a conventional pipette to simultaneously test drug permeability and efficacy, was developed by growing cells in the extracellular matrix (ECM) layer in a hole at the outlet (bottom) of E-PAT. In the existing permeability/efficacy assay technique conducted using the transwell assays, the Cell/ECM layers were formed on permeable polymer membranes; however, the production of small membranes to realize transwell miniaturization is expensive and difficult. To resolve this issue, in the proposed approach using E-PAT, small Cell/ECM layers were formed in the hole at the outlet (bottom) of the tip without membranes. A pipette was connected to the E-PAT to easily aspirate the Cell/ECM mixture into the hole of the tip, allowing the formation of miniature Cell/ECM layers at the bottom of the tip. Subsequently, the E-PAT was detached from the pipette and dipped into a well filled with media. The cells in the ECM grew three-dimensionally and made Cell/ECM layer in the E-PAT. The permeability/efficacy assays were performed using the Cell/ECM layer in E-PAT. The compounds or nanoparticles supplied through the inlet (hole) at the top of the E-PAT penetrated the Cell/ECM layers and were diluted by the media in the well. By measuring the concentration of the compounds or nanoparticles in the well and the cell viability in the Cell/ECM layer, the permeability and efficacy/cytotoxicity of the compounds in the proposed E-PAT could be concurrently estimated with a high throughput. In particular, E-PAT measured the IC50 (half maximal inhibitory concentration) for 3.383 μM doxorubicin (DOX) and indicated that 73 % 4 μM DOX penetrated the Cell/ECM layers, inducing the death of 57.2 % HepG2 cells. Moreover, the device demonstrated that FITC-SiO2 nanoparticles with a diameter of 25 nm permeated higher into the ECM and killed more HepG2 cells under the serum (fetal bovine serum, FBS) free media conditions than under the serum containing media conditions. The E-PAT could thus measure the compound efficacy as well as the compound permeability. The proposed tip can be a valuable tool to determine whether the efficacy/cytotoxicity of a compound is because of its low permeability.

Nanoparticles can be valuable therapeutic options to overcome physical barriers to reach central nervous system. Systemically administered nanoparticles can pass through blood-neural barriers; whereas, locally injected nanoparticles directly reach neuronal and perineuronal cells. In this review, we highlight the importance of size, surface charge, and shape of nanoparticles in determining therapeutic effects on brain and retinal diseases. These features affect overall processes of delivery of nanoparticles: in vivo stability in blood and other body fluids, clearance via mononuclear phagocyte system, attachment with target cells, and penetration into target cells. Furthermore, they are also determinants of nano-bio interfaces: they determine corona formation with proteins in body fluids. Taken together, we emphasize the importance of considerations on characteristics of nanoparticles more suitable for the treatment of brain and retinal diseases in the development of nanoparticle-based therapeutics. From the Clinical Editor The central nervous system (CNS) remains an area where drug access and delivery are difficult clinically due to the blood brain barrier. With advances in nanotechnology, many researchers have designed and produced nanoparticle-based systems in an attempt to solve this problem. In this concise review, the authors described the current status of drug delivery to the CNS, based on particle size and shape. This article should stimulate more research to be done on future drug design.

Local application requires fewer nanoparticles than systemic delivery to achieve effective concentration. In this study, we investigated the potential toxicity and efficacy of bare titanium dioxide (TiO 2 ) nanoparticles by local administration into the eye. Mono-disperse, 20 nm-size TiO 2 nanoparticles did not affect the viability of retinal constituent cells within certain range of concentrations (~ 1.30 μg/mL). Furthermore, local delivery of TiO 2 nanoparticles did not induce any significant toxicity at the level of gene expression and histologic integrity in the retina of C57BL/6 mice. Interestingly, at the low concentration (130 ng/mL) without definite toxicity, these nanoparticles suppressed in vitro angiogenesis processes and in vivo retinal neovascularization in oxygen-induced retinopathy mice when they are administered intravitreally. Taken together, our results demonstrate that even TiO 2 nanoparticles can be safely utilized for the treatment of retinal diseases at the adequate concentration levels, especially through local administration. From the Clinical Editor In this paper the local application of titanium dioxide is described as a local treatment for retinal diseases associated with neovascularization. While these nanoparticles have known systemic toxicity, this work demonstrates that when applied locally in a mouse model, they can be used without observable toxicity even in their native forms.

We report a gold substrate manipulation from very-flat to highly-curved surfaces with a thermal treatment as a function of annealing temperature, which greatly affects the quality of SAM with respect to density and ordering. Annealing of gold film greatly removes nanometer-scale protrusions, leading to a very-flat surface with a large grain size as comparable with gold coating on mica. The quality of alkanethiol SAM are evaluated using Fourier transform infrared and time of flight secondary ion mass spectroscopy. Our proposed method delivers good ordering between molecules in the SAMs to promote a high density on extremely small areas for a cost-effective and miniaturized biochip.

Objective Changes in cholesterol ester (CE) content regulate the progression of atherosclerosis. However, the spatial dynamics of CE subsets and their quantitative changes during lesion progression are not well understood due to a lack of appropriate imaging techniques. In this study, we developed an imaging–based analysis method to map the distribution of CE subsets using time-of-flight secondary ion mass spectrometry (ToF-SIMS). Methods Serial sections of atherosclerotic aortic sinuses from apolipoprotein E knock-out mice ( n = 15) fed a 0.15% high-fat diet for 12–20 weeks were examined by ToF-SIMS. Results and conclusion We found that the ratio of cholesteryl palmitate (Ch-PA) to cholesteryl oleate (Ch-OA) increased by approximately 99% ( p = 0.02) as atherosclerosis progressed, whereas the ratios of cholesteryl linoleate ( p = 0.09) and cholesteryl stearate ( p = 0.22) to Ch-OA did not change significantly. In advanced atherosclerotic plaques, in situ and in-vitro cell death assays showed that local Ch-PA densities were highly correlated with an increase in the number of apoptotic cells. These results suggest that increased Ch-PA may contribute to the formation of a necrotic core by increasing cell death. Our results indicate that the regional ratio of CEs as measured by ToF-SIMS might be a valuable new marker of atherosclerotic progression.

Long tungsten oxide nanorods are vertically grown on Al/W/Ti coated silicon substrates using a two-step anodization process. The first anodization of the Al film forms a mesh-like mask of anodic aluminum oxide, and the second anodization of the W film results in the formation of a buffer layer, a bottom nanorod, and a top nanorod of amorphous tungsten oxide. A pore-widening process prior to the second anodization leads to the enhancement of nanorod length above approximately 500 nm. After a heat-treatment, the tungsten oxide nanorods are crystallized to form a single crystalline structure while the buffer layer forms a polycrystalline structure. The crystalline tungsten oxide nanorods show a cyclic voltammogram retaining the quasi-rectangular shape of an electrochemically reversible faradaic redox reaction, i.e., a typical pseudocapacitive behavior. The maximum electrochemical capacitance per apparent surface area reaches approximately 2.8 mF cm −2 at the voltage scan rate of 20 mV s −1 , and the excellent cyclability of charge–discharge process is maintained up to 1000 cycles.

Angiogenesis-related blindness indicates the spectrum of retinal diseases that are caused by pathological angiogenesis, resulting in catastrophic vision loss. We aimed to demonstrate the antiangiogenic effect of silicate nanoparticles (SiNPs) on the retinal neovascularization. No direct toxicity of SiNPs was observed on retinal neuronal or endothelial cells, nor on the retinal tissue. Furthermore, intravitreal injection of SiNPs effectively reduced anomalous retinal angiogenesis in oxygen-induced retinopathy mice. SiNPs also effectively inhibited in vitro vascular endothelial growth factor (VEGF)-induced angiogenesis. Via suppression of VEGF receptor-2 phosphorylation induced by VEGF, SiNPs blocked ERK 1/2 activation. SiNPs could be an inhibitor of the potency and safety of retinal neovascularization that is mediated by VEGF and utilized in the treatment of angiogenesis-related blindness. From the Clinical Editor In this important preclinical study, silicate NP-s are studied to address retinal neovascularization, an important pathomechanism of different retinal diseases that could lead to catastrophic vision loss. The authors conclude that SiNP-s could be utilized as inhibitors of retinal neovascularization mediated by VEGF and propose future applications in the treatment of angiogenesis-related blindness.

Simultaneous measurement of growth morphology and electronic energy level alignment for pentacene layers on silicon oxide before and after the octadecyltrichlorosilane (OTS) self-assembled monolayer treatment has been carried out by photoemission electron microscopy (PEEM) and ultraviolet photoelectron spectroscopy (UPS). On the bare silicon oxide, the change of the highest occupied molecular orbital (HOMO) position with the pentacene thickness is marginal because of relatively strong interaction between the substrate and pentacene from the beginning. On the OTS-covered surface, due to the weak interaction between the substrate and pentacene, the diffusion of pentacene is enhanced and domain size gradually grows, leading to more or less standing-up orientation of the pentacene molecules. This comparison explains well the substrate-dependent growth morphology and interfacial dipole change of pentacene thin films.

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.

The pathological angiogenesis in the retina is the major cause of vision loss at all ages. In particular, retinopathy of prematurity (ROP) is a leading cause of blindness in children. This study investigated whether gold nanoparticle (GNP) could inhibit retinal neovascularization in the animal model of ROP. Intravitreal injection of GNP significantly inhibited retinal neovascularization in the mouse model of ROP. In addition, GNP effectively suppressed VEGF-induced in vitro angiogenesis of retinal microvascular endothelial cells including proliferation, migration and capillary-like networks formation. GNP blocked VEGF-induced auto-phosphorylation of VEGFR-2 to inhibit consequently ERK 1/2 activation. GNP never affected on the cellular viability of retinal microvascular endothelial cells and induced no retinal toxicity. Our data suggest that GNP could be a potent inhibitor to retinal neovascularization without retinal toxicity. Furthermore, GNP could be extensively applied to variable vaso-proliferative retinopathies mediated by VEGF.

With the development of optimal surface cleaning techniques by cluster ion beam sputtering, certain applications of SIMS for analyzing cells and tissues have been actively investigated. For this report, we collaborated with bio-medical scientists to study bio-SIMS analyses of skin and cancer tissues for biomedical diagnostics. We pay close attention to the setting up of a routine procedure for preparing tissue specimens and treating the surface before obtaining the bio-SIMS data. Bio-SIMS was used to study two biosystems, skin tissues for understanding the effects of photoaging and colon cancer tissues for insight into the development of new cancer diagnostics for cancer. Time-of-flight SIMS imaging measurements were taken after surface cleaning with cluster ion bombardment by Bin or C60 under varying conditions. The imaging capability of bio-SIMS with a spatial resolution of a few microns combined with principal component analysis reveal biologically meaningful information, but the lack of high molecular weight peaks even with cluster ion bombardment was a problem. This, among other problems, shows that discourse with biologists and medical doctors are critical to glean any meaningful information from SIMS mass spectrometric and imaging data. For SIMS to be accepted as a routine, daily analysis tool in biomedical laboratories, various practical sample handling methodology such as surface matrix treatment, including nano-metal particles and metal coating, in addition to cluster sputtering, should be studied.

Enhancement of signals in time-of-flight secondary ion mass spectrometry (ToF-SIMS) studies is necessary to many biological applications. We have developed an efficient method of enhancing the signals of secondary ions from peptides using gold nanoparticles (AuNPs) attached to a well-controlled surface such as self-assembled monolayers (SAMs). AuNPs function as both signal enhancers and effective binding sites for peptides, which allow the high signal intensity from the peptides to produce well-contrasted ToF-SIMS images of peptides that are micropatterned on the surface of the AuNPs. For application, this AuNP-enhanced SIMS (NE-SIMS) provided the basis for the spectrum and images to assay protein kinases and their inhibitors. Phosphorylation efficiency and inhibitor effect were quantified by detecting mass change of the peptide substrates by kinase reaction. Maximum efficiency of phosphorylation was achieved from cysteine-tethered peptides with a spacer linker, indicating that accessibility of kinase was dependent on the surface orientation and length of the peptide substrate on the three-dimensional AuNPs. The activities of other enzymes such as phosphatase and protease could also be assayed using NE-SIMS. Our study shows that NE-SIMS can be applied as a useful tool for enzyme assay in biochip surfaces.

The production of reproducible self-assembled monolayers (SAMs) is essential to many nano(bio)technology applications. To check the effects of different cleaning methods on a reproducible SAMs formation, the cleaning methods were varied and then used for preparing each SAM. The reproducibility of each SAM was examined by ToF-SIMS analysis along with principal component analysis (PCA). Using what we found to be a superior method of cleaning gold surfaces, alkanethiol SAMs with different terminal groups such as 1-dodecanethiol (DDT), 11-mercaptoundecanoic acid (MUA), 11-mercapto-1-undecanol (MUD) were reproduced. Our statistical results show that reproducible alkanethiol SAMs on a well-cleaned gold surface can be produced within only a few standard deviation percentages obtained from point-to-point and sample-to-sample spectra.

Human normal colon mucosa and colon cancer tissue were studied using the time-of-flight secondary ion mass spectroscopy (ToF-SIMS) and principal component analysis (PCA) techniques. The surfaces of the tissues were successfully cleaned by C602+ cluster-ion beams before the ToF-SIMS images were obtained. A PCA on the spectra and images were performed to compare differences in the peaks and images of normal and cancer tissues. Significant differences in principal component 1 (PC 1) score values for normal and cancer tissues were observed, and each PC 1 loadings had a specific peak profile of proteins. In addition, the PC images obtained from the ToF-SIMS images for normal and cancer tissues were clearly distinguishable, and the amino acid fragments associated with normal and cancer tissues were found to have originated from the lamina propria region and the epithelium cells, respectively. Based on the PCA results, structural distortion of the crypts in the cancer colon tissue could be attributed to the proliferation of the cancerous epithelium cells. This work shows that the application of the ToF-SIMS imaging technique with PCA could be a useful method of obtaining valuable information for cancer analysis.

A quantitative analysis of the surface density of amine groups on a plasma-polymerized ethylenediamine thin film deposited on a platinum surface using inductively coupled plasma chemical vapor deposition method is described. UV–visible spectroscopy together with a chemical derivatization technique using Fourier transform infrared (FT-IR) spectroscopy was used to obtain the quantitative information. Chemical tags of pentafluorobenzaldehyde were hybridized with the surface amine groups and were easily detected due to the characteristic absorption bands of C–F stretching, aromatic ring and C N stretching vibrations in the reflection–absorption FT-IR spectra. The surface amine density was reproducibly controlled as a function of deposition plasma power and quantified using UV–visible spectroscopy. A good linear correlation was observed between the FT-IR intensities of the characteristic absorption bands and the surface amine densities, suggesting the possibility of using this chemical derivatization technique to quantify the surface densities of specific functional groups on an organic surface. Chemical derivatization was also used with X-ray photoelectron spectroscopy on the same samples, and the results were compared with those obtained from FT-IR and time-of-flight secondary ion mass spectrometry. Although each analysis technique has different probing depths from the surface, the three different data sets obtained from the chemical tags correlated well with each other since each analysis technique measured the chemical tags on the sample surface.

The mechanical properties of epitaxial ZnO thin films grown on (0 0 0 1) sapphire substrate were investigated by nanoindentation with a Berkovich tip and compared with that of bulk ZnO single crystal. In all indents on ZnO film a single discontinuity (‘pop-in’) in the load versus indentation depthdatawasobservedataspecificdepthofbetween13and 16 nm.InbulkZnO,howeveronly65%ofindents showedpop-ineventat a specific depth of between 12 and 20 nm. The mechanism responsible for the ‘pop-in’ event in the epitaxial ZnO thin films as well as in bulk ZnO was attributed to the sudden propagation of dislocations, which had been pinned down by pre-existing defects, along the pyramidal 10 ¯ fg and basal {0 0 0 1} planes (cross slip). The elastic modulus and hardness of the epitaxial ZnO thin films were determined to be 154 � 5 and 8.7 � 0.2 GPa, respectively, at an indentation depth of 30 nm. # 2005 Elsevier B.V. All rights reserved.

Nanoindentation studies have been carried out on undoped and doped epitaxial GaN thin films with different thickness (1–4m) were grown epitaxially on c-plane sapphire substrate by metalorganic chemical vapor deposition (MOCVD). Multiple discontinuities (so-called ‘pop-in’ events) were observed in the load–indentation depth curve irrespective of the thickness as well as the doping condition. Atomic force microscopy (AFM) studies on the residual indentation impression revealed no micro-cracks even after the indentation beyond the critical depth. The physical mechanism responsible for the ‘pop-in’ was explained by the interaction of the deformed region, produced by the indenter tip, with the pre-existing threading dislocation in the epitaxial GaN thin films. © 2005 Elsevier B.V. All rights reserved.

A chemical derivatization technique in ToF-SIMS along with principal component analysis (PCA) were used to perform a quantitative study of the surface amine density of the plasma-polymerized ethylenediamine (PPEDA) thin film. We used the scores on principal component (PC) 1 from a PCA of ToF-SIMS data for the PPEDA films and their chemical-derivatized surfaces for comparison with the surface amine densities. These surface amine densities were independently determined by UV–visible spectroscopy. Our work found a good linear relationship between the surface amine densities and the scores on PC 1 from a PCA of the ToF-SIMS data for the chemical-derivatized PPEDA surfaces, but not for the PPEDA thin films themselves. In addition to quantification, our PCA results provided insights into the surface chemical composition of each surface.

ToF-SIMS analysis with principal component analysis (PCA) has been used for quantitatively studying the interaction between streptavidin and biotin on a dendrimer surface. A poly(amidoamine) dendrimer surface was used as a model amine surface for biotinylation. The surface streptavidin density was systematically varied and independently quantified using the surface plasmon resonance (SPR) technique. A good linear correlation of streptavidin density was observed between the ToF-SIMS and SPR results.

The photochemistry of CH 3 Br adsorbed on CaF 2 has been studied using CaF 2 (111) modified by (a) low-energy electron impact and (b) dosing with hydrogen atoms. In each case the temperature-programmed desorption (TPD) behaviour and the photodynamics, i.e. the energy and angular distributions of the photoformed methyl radicals were compared with the same diagnostics applied to unmodified CaF 2 (111). Electron irradiation of the CaF 2 (111) surface resulted in an increased desorption temperature of the adsorbate, and the emergence of a broadened translational energy photodissociation channel, P ( E T ′), for CH 3 (g), associated in earlier work with photoinduced charge-transfer dissociation of the adsorbate. This suggested the formation of Ca metal clusters by process (a). By contrast, the hydrogen-atom-modified surface exhibited a decreased desorption temperature of the adsorbate and no broadening of P ( E T ′). The thermal hydrogen atoms may modify the surface by abstracting surface F, forming HF(g). Electron impact and hydrogen atom modification of the CaF 2 changed the angular distributions for the ‘directly formed’ (fast) CH 3 (g) photofragments in a markedly different fashion, indicative of differing structure in the adlayer for CaF 2 (111) when modified by processes (a) or (b).

Methyl photofragments from the 193 nm photodissociation of CH3Br adsorbed on CaF2(111) were studied by angularly resolved time-of-flight mass spectrometry. The translational energy distributions, P(ET′), of the CH3 photofragments showed evidence of four pathways, depending on the coverage. The pathways were termed ‘direct’ (DIR), ‘indirect(1′)’ [IND(1′)], ‘indirect(1)’ [IND(1)] and ‘indirect(2)’ [IND(2)] in order of decreasing peak ET′. The DIR methyl P(ET′) peaked at 2.4 eV, with a full-width at half-maximum (FWHM) of 0.6 eV, corresponding closely to that reported for gas-phase CH3 (peak=2.5 eV, FWHM=0.5 eV). The P(ET′) of this DIR pathway was consistent with CH3 escaping directly without collisions. For these DIR methyls the angular distribution, P(θ′), reflected the prior BrC bond direction at the various coverages. The DIR P(θ′) indicated a change in the alignment of BrCH3 with increasing coverage, from one in which the Br–C axis was initially roughly parallel to the surface plane (0.25 ML), to one with the Br–C axis along the surface normal (0.5 and 2 ML), and finally to one with the Br–C axis 23° from the surface normal (7 ML). The IND(1′) and IND(1) methyls, despite an energy loss of 0.7 and 1.3 eV, respectively, in a strong inelastic encounter, both exhibited similar energy and angular distributions to the DIR component. We propose that the IND(1) pathway is due to the occurrence of an ‘intralayer’ exchange reaction ( C H 3 +BrCH 3 ′→CH 3 Br+C H 3 ′ ) in one layer, and in the case of the IND(1′) pathway the same process occurring in ‘interlayer’ collisions, since IND(1′) methyls were only observed at ∼2 ML coverage. This methyl-exchange reaction has been invoked previously to explain a similar inelastic pathway observed for photorecoiling CH3 coming from CH3Br on LiF(001), NaCl(001) and MgO(001). The IND(2) pathway was characterized by a broader P(ET′) than the other three pathways, and a broad P(θ′) (cosn θ′, n=1.7–3.8), peaking at the surface normal. These attributes of P(θ′) for IND(2) are characteristic of strongly inelastic encounters in which memory of the initial BrC bond direction is lost.

The effects of C60 cluster ion beam bombardment in sputter depth profiling of inorganic–organic hybrid multiple nm thin films were studied. The dependence of SIMS depth profiles on sputter ion species such as 500 eV Cs+, 10 keV C60+, 20 keV C602+ and 30 keV C603+ was investigated to study the effect of cluster ion bombardment on depth resolution, sputtering yield, damage accumulation, and sampling depth.

Interaction between streptavidin and biotin on poly(amidoamine) (PAMAM) dendrimer-activated surfaces and on self-assembled monolayers (SAMs) was quantitatively studied by using time-of-flight secondary ion mass spectrometry (ToF-SIMS). The surface protein density was systematically varied as a function of protein concentration and independently quantified using the ellipsometry technique. Principal component analysis (PCA) and principal component regression (PCR) were used to identify a correlation between the intensities of the secondary ion peaks and the surface protein densities. From the ToF-SIMS and ellipsometry results, a good linear correlation of protein density was found. Our study shows that surface protein densities are higher on dendrimer-activated surfaces than on SAMs surfaces due to the spherical property of the dendrimer, and that these surface protein densities can be easily quantified with high sensitivity in a label-free manner by ToF-SIMS.

The spacing of chemical functional groups on self-assembled monolayers (SAMs) plays an important role in controlling the density of biomolecules in biochips and biosensors. In this sense, a mixed SAM made of two different terminal groups is a useful organic surface since spacing can be easily controlled by changing a relative mole fraction in a mixture solution. In this study, an acetylene–OCH2O(EG)3(CH2)11S–S(CH2)11(EG)3OCH2O–propene (Eneyne) SAM and mixed SAMs made by a mixture of (S(CH2)11(EG)3OCH2O–acetylene)2 (Diyne) and (S(CH2)11(EG)3OCH2O–propene)2 (Diene) were produced on gold substrates and measured by using ToF-SIMS. The secondary ion yield ratio of [Au·S(CH2)11(EG)3OCH2O–acetylene]− to [Au·S(CH2)11(EG)3OCH2O–propene]− was measured for each mixed SAM and plotted as a function of the mole fraction of Diyne to Diene in a SAM solution. The ion yield ratio of a mixed SAM produced from a solution with a mole fraction of 0.5 (i.e., 1:1 mixture) was 0.3, which corresponded well to the ion yield ratio measured from an Eneyne SAM. A time-dependent experiment of Eneyne SAM formation and immersion experiment of Eneyne SAM into Diyne solution or into Diene solution were performed. The relative ion yield ratio of 0.3 was due to a different secondary ion formation and not due to the difference in the amount of adsorbates on the surface, nor to the different binding strengths onto the gold surface. Our study shows that a mixed SAM with well-controlled spacing can be produced and quantified by using the ToF-SIMS technique.

Nanoindentation studies were carried out on epitaxial ZnO thin films on (0001) sapphire substrates grown by radio frequency magnetron sputtering. A single discontinuity (‘pop-in’) in the load–displacement curve was observed at a specific depth (13−16 nm) irrespective of the film thickness. The physical mechanism responsible for the ‘pop-in’ event in these epitaxial films may be due to the nucleation, propagation and interaction behavior of the glissile threading dislocations during mechanical deformation. Indentation well below the critical depth was found to be plastic deformation behavior (residual impression of 4 nm).

A ToF-SIMS imaging technique has been used to obtain dye label-free chemical images of gradient polyethylene (PE) and its amine-functionalized surfaces. The gradient PE surface was prepared by a corona treatment with a power increase along the PE length and confirmed by ToF-SIMS. Amine reagents with varying molecular weights (MW 158, 600, 1200, 10,000 and 60,000) were successively reacted with a gradient PE surface and examined using ToF-SIMS. Our work found that the lower the molecular weight of amine reagent, the more gradient surface of amine surface density was generated. The amine-functionalized gradient surface can be used as a template surface for evaluating bioactive molecules on the gradient surface in just one experiment.

The exit channel dynamics of the four-centered elimination CH 2 OH + →CHO + +H 2 is investigated by a classical trajectory calculation on the analytic potential energy surface reported previously (J. Chem. Phys. 104 (1996) 4517). The rotational and relative translational energies of the two separating moieties and the total vibrational energy are calculated as a function of the distance between their centers of mass. Rotational and vibrational energies are found to be determined shortly after the sustem leaves the transition state. Thereafter, the remainder of the reverse barrier is mostly converted to the relative translational energy. Hence, a shift technique may be used to estimate the kinetic energy release distribution for the products from the translational energy distribution obtained from the middle of the exit channel motion.

The lipid crystals are one of the important hallmarks of advanced atherosclerotic plaques. However, the detailed assessment of lipid crystals including their chemical compositions and morphological information at the tissue level are little known due to the lack of appropriate imaging techniques. Here, we developed a combinational method to characterize the morphology of lipid crystals precisely and concomitantly to identify their chemical compositions based on coherent anti-stokes raman scattering (CARS) spectroscopy and time-of-flight secondary-ion-mass-spectroscopy (ToF-SIMS). To accelerate the progression of atherosclerosis, partial ligation surgery of left carotid artery (LCA) in apolipoprotein E knock-out mice (n=26) was performed. The change of lipid crystals during the progression of atherosclerosis was studied by feeding high-fat diet for 1-8 weeks. We found the transition of chemical composition from oleate to the palmitate of atherosclerotic lipids at intermediate stage. Lipid crystals at advanced stage were dominantly observed at the inner side of internal elastic lamina and their distribution was clearly distinguished from other types of lipids. We also found that the lipid crystals showed distinct physical spectrum comparing to intra/extracellular lipid droplets by spectral CARS analysis. The same region of lipid crystals was subjected to investigation of chemical compositions using ToF-SIMS. We found that palmitate (m/z 255.2), a saturated fatty acid, was dominated in lipid crystal regions in advanced atherosclerotic stage. The developed technology based on the combination of CARS and ToF-SIMS could simultaneously provide the detailed lipid morphology with high resolution and chemical information correlating to their morphology. We expect that the results of lipid crystals with developed imaging platform could be further extended to better understanding for the mechanisms of plaque rupture.

A pellet of silver benzenethiolate shows strong surface-enhanced Raman scattering (SERS) after prolonged laser illumination. X-ray photoelectron spectroscopic and scanning electron microscopic studies show that the SERS activity arises via the photoformation of Ag islands on the pellet surface.