Tip-enhanced Raman spectroscopic imaging shows segregation within binary self-assembled thiol monolayers at ambient conditions.

Phase segregation of coadsorbed thiol molecules on a gold surface was investigated with nanoscale chemical imaging using tip-enhanced Raman spectroscopy (TERS). Samples were prepared using mixed solutions containing thiophenol (PhS) and an oligomeric phenylene-ethynylene (OPE) thiol, with 10:1, 2:1, and 1:1 molar ratios. Phase segregation into domains with sizes from ≈30 to 240 nm is observed with these molar ratios. A comparison of TERS images with different pixel sizes indicates that a pixel size bigger than 15 nm is not reliable in defining nanodomains, because of undersampling. In this study, the formation of nanodomains was clearly evident based on the molecular fingerprints provided by TERS, while ambient scanning tunneling microscopy (STM) was not capable of discerning individual domains via their apparent height difference. TERS therefore allows to image nanodomains in binary self-assembled monolayers, which are invisible to methods solely relying on topographic or electron density characteristics of self-assembled monolayers. Moreover, TERS mapping provides statistical data to describe the distribution of molecules on the sample surface in a well-defined manner. Peak ratio histograms of selected TERS signals from samples prepared with different mixing ratios give a better understanding of the adsorption preference of the thiols studied, and the relationship of their mixing ratio in solution and adsorbed on the surface.

Systematic study of polymer gas sampling bags for offline analysis of exhaled breath.

Polymeric bags are a widely applied, simple, and cost-effective method for the storage and offline analysis of gaseous samples. Various materials have been used as sampling bags, all known to contain impurities and differing in their cost, durability, and storage capabilities. Herein, we present a comparative study of several well-known bag materials, Tedlar (PVF), Kynar (PVDF), Teflon (PTFE), and Nalophan (PET), as well as a new material, ethylene vinyl copolymer (EVOH), commonly used for storing food. We investigated the influences of storage conditions, humidity, bag cleaning, and light exposure on volatile organic compound concentration (acetone, acetic acid, isoprene, benzene, limonene, among others) in samples of exhaled human breath stored in bags for up to 48 h. Specifically, we show high losses of short-chain fatty acids (SCFAs) in bags of all materials (for most SCFAs, less than 50% after 8 h of storage). We found that samples in Tedlar, Nalophan, and EVOH bags undergo changes in composition when exposed to UV radiation over a period of 48 h. We report high initial impurity levels in all the bags and their doubling after a period of 48 h. We compare secondary electrospray ionization and proton transfer reaction mass spectrometry in the context of offline analysis after storage in sampling bags. We provide an analytical perspective on the temporal evolution of bag contents by presenting the intensity changes of all significantm/zfeatures. We also present a simple, automated, and cost-effective offline sample introduction system, which enables controlled delivery of collected gaseous samples from polymeric bags into the mass spectrometer. Overall, our findings suggest that sampling bags exhibit high levels of impurities, are sensitive to several environmental factors (e.g. light exposure), and provide low recoveries for some classes of compounds, e.g. SCFAs.

Use of polyetheretherketone as a material for solid phase extraction of hydroxylated metabolites of polycyclic aromatic hydrocarbons in human urine.

In this study, a novel application of polyetheretherketone (PEEK) tubing for solid phase extraction (SPE) of urinary hydroxylated metabolites of polycyclic aromatic hydrocarbons (OH-PAHs) is presented. The use of PEEK tubing for extracting nine OH-PAHs (2-5 rings) from different matrixes (e.g., urine, acid/enzymatic hydrolysis solution) was demonstrated; a facile method for fast (<2 min) quantification of urinary 1-hydroxypyrene (1-OHPyr) was also developed by the use of PEEK tubing extraction coupled to electrospray ionization tandem mass spectrometry (ESI-MS/MS). Although no optimization was performed for the extraction process, a limit of detection (LOD) as low as 0.01 µg L(-1) was obtained, and the ratio of signal intensity of 1-OHPyr to that of 1-OHPyr-d9 (internal standard) was linearly related with the 1-OHPyr concentration over the range of 0.05-5.00 µg L(-1) (R(2) = 0.9995). Satisfactory recoveries (87-91%) were achieved, and less than 2 min was required to carry out the whole analytical procedure including sample pretreatment and mass spectrometric detection. In a biomonitoring study, the PEEK tubing extraction based method was successfully applied to the quantification of 1-OHPyr in eight human urine samples, further confirming the potential of PEEK tubing for SPE of organic compounds.

Nanoscale chemical imaging of segregated lipid domains using tip-enhanced Raman spectroscopy.

Lipid domains in supported lipid layers serve as a popular model to gain insight into the processes associated with the compartmentalization of biological membranes into so-called lipid rafts. In this paper, we present reproducible tip-enhanced Raman spectra originating from a very small number of molecules in a lipid monolayer on a gold surface, probed by the apex of a nanometer-sized silver tip. For the first time, we show large (128 × 128 pixels), high-resolution (< 50 nm) tip-enhanced Raman images of binary lipid mixtures with full spectral information at each pixel.

Nanoscale probing of a polymer-blend thin film with tip-enhanced Raman spectroscopy.

Fundamental advances have been made in the spatially resolved chemical analysis of polymer thin films. Tip-enhanced Raman spectroscopy (TERS) is used to investigate the surface composition of a mixed polyisoprene (PI) and polystyrene (PS) thin film. High-quality TER spectra are collected from these nonresonant Raman-active polymers. A wealth of structural information is obtained, some of which cannot be acquired with conventional analytical techniques. PI and PS are identified at the surface and subsurface, respectively. Differences in the band intensities suggest strongly that the polymer layers are not uniformly thick, and that nanopores are present under the film surface. The continuous PS subsurface layer and subsurface nanopores have hitherto not been identified. These data are obtained with nanometer spatial resolution. Confocal far-field Raman spectroscopy and X-ray photoelectron spectroscopy are employed to corroborate some of the results. With routine production of highly enhancing TERS tips expected in the near future, it is predicted that TERS will be of great use for the rigorous chemical analysis of polymer and other composite systems with nanometer spatial resolution.

Fast polymer fingerprinting using flowing afterglow atmospheric pressure glow discharge mass spectrometry.

Flowing afterglow atmospheric pressure glow discharge mass spectrometry (FA-APGD-MS) was used to interrogate different polymer species such as biopolymers, synthetic homo- and co-polymers. The main advantages of FA-APGD-MS for polymer samples include speed (<30 s per sample) and analysis at atmospheric pressures. Moreover, there are essentially no restrictions as to the kind of polymer sample that can be analyzed because FA-APGD-MS can deal with liquid and solid (soluble or insoluble) bulk polymers and granulates, irrespective of their conductivity, without requiring any sample preparation prior to analysis. We will discuss the mechanism of ion formation as well as the limitation of the accessible mass range (m/z < 500) in view of what type of information can be gained from the mass spectra obtained. Monomer units and some fragments were detected for homopolymers, e.g.cis-polyisoprene (IR), poly(ethylene glycol) (PEG), poly(ethylene terephthalate) (PET), which allowed identification of the polymer composition. The mass spectra obtained were further processed using principal component analysis (PCA) for a better visualization and assessing of mass-spectral reproducibility. Combination with PCA even allowed differentiation of pectin, amylopectin, and cellulose, chemically very similar polysaccharides whose characteristic differences lie in the nature of the glycosidic linkage. Finally, we were able to detect and identify phthalate plasticizers, bis(2-ethylhexyl) phthalate (BEHP) and dibutyl phthalate (DBP), present in poly(vinyl chloride)-based food wraps.

Polystyrene beads as an alternative support material for epitope identification of a prion-antibody interaction using proteolytic excision-mass spectrometry.

The binding epitope structure of a protein specifically recognized by an antibody provides key information to prevent and treat diseases with therapeutic antibodies and to develop antibody-based diagnostics. Epitope structures of antigens can be effectively identified by the proteolytic epitope excision-mass spectrometry (MS) method, which involves (1) immobilization of monoclonal or polyclonal antibodies, e.g., on N-hydroxysuccinimide-activated sepharose, (2) affinity binding of the antigen followed by limited proteolytic digestion of the immobilized immune complex, and (3) elution and mass spectrometric analysis of the remaining affinity-bound peptide(s). In the epitope analysis of recombinant cellular bovine prion protein (bPrP(C)) to a monoclonal antibody (mAb3E7), we found that epitope excision experiments resulted in extensive nonspecific binding of bPrP to a standard sepharose matrix employed. Here, we show that the use of amino-modified polystyrene beads with aldehyde functionality is an efficient alternative support for antibody immobilization, suitable for epitope excision-MS, with complete suppression of nonspecific bPrP binding.

Metabolic changes during periodontitis therapy assessed by real-time ambient mass spectrometry.

It has been shown that bacteria in periodontally diseased patients can be recognized by the detection of volatile metabolites in the headspace of saliva by real-time ambient mass spectrometry. The aim of this study was to use this detection method to analyze the oral metabolome in diseased periodontitis patients before and after therapy to monitor disease evolution and healing events. Twelve patients with advanced chronic periodontal disease and 12 periodontally healthy controls served as test and control groups, respectively. Clinical data, subgingival plaque samples and saliva samples were collected at baseline (BL) and 3 months after treatment. The test group received non-surgical scaling and root planing using systemic antibiotics and the control group received one session of supragingival cleaning. Saliva samples from all subjects were analyzed with ambient mass spectrometry. Significant metabolic alterations were found in the headspace of saliva of periodontitis patients 3 months after the non-surgical periodontal treatment. Furthermore, the diseased group showed metabolic features after the treatment that were similar to the healthy control group. In addition, 29 metabolic features correlated with A. actinomycetemcomitans, 17 features correlated with P. gingivalis and one feature correlated with T. denticola. It was shown that headspace secondary electrospray ionization - mass spectrometry allows the detection of different volatile metabolites in healthy and diseased patients. It can be concluded that this rapid and minimally invasive method could have the potential to routinely diagnose and monitor periodontal diseases in the headspace of saliva samples and, eventually, in exhaled breath.

Manipulation of charge states of biopolymer ions by atmospheric pressure ion/molecule reactions implemented in an extractive electrospray ionization source.

A home-made extractive electrospray ionization source is coupled to an linear quadrupole ion trap mass spectrometer to investigate ion/molecule reactions of biopolymers at ambient pressure. Multiply charged biopolymers such as peptides and proteins generated in an electrospray are easily reduced to a low charge state by the atmospheric pressure ion/molecule reactions occurring between the multiply charged ions and a strong basic reagent sprayed in neutral form into the electrospray plume. The charge state of the biopolymer ions can be manipulated by controlling the amount of the basic reagent. The production of biopolymer ions with low charge states results in a substantial improvement of sensitivity and reduced spectral congestion in ESI-MS. This is of importance for biopolymer mixture analysis and could have promising applications in proteomics.

Differentiation of oral bacteria in in vitro cultures and human saliva by secondary electrospray ionization - mass spectrometry.

The detection of bacterial-specific volatile metabolites may be a valuable tool to predict infection. Here we applied a real-time mass spectrometric technique to investigate differences in volatile metabolic profiles of oral bacteria that cause periodontitis. We coupled a secondary electrospray ionization (SESI) source to a commercial high-resolution mass spectrometer to interrogate the headspace from bacterial cultures and human saliva. We identified 120 potential markers characteristic for periodontal pathogens Aggregatibacter actinomycetemcomitans (n = 13), Porphyromonas gingivalis (n = 70), Tanerella forsythia (n = 30) and Treponema denticola (n = 7) in in vitro cultures. In a second proof-of-principle phase, we found 18 (P. gingivalis, T. forsythia and T. denticola) of the 120 in vitro compounds in the saliva from a periodontitis patient with confirmed infection with P. gingivalis, T. forsythia and T. denticola with enhanced ion intensity compared to two healthy controls. In conclusion, this method has the ability to identify individual metabolites of microbial pathogens in a complex medium such as saliva.

The influence of grain size on low-temperature degradation of dental zirconia.

UNLABELLED: The purpose of this study was to evaluate the influence of grain size and air abrasion on low-temperature degradation (LTD) of yttria stabilized tetragonal zirconia polycrystalline (Y-TZP). Disc-shaped specimens were sintered at 1350, 1450, and 1600°C. Air abrasion was performed with different abrasive particles. The specimens were stored for 2 h at 134°C under 2.3 bar water vapor pressure. All specimens were characterized by X-ray powder diffraction analysis (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and field emission scanning electron microscopy (FESEM). Y-TZP sintered at a temperature of 1350°C did not undergo the t-m phase transformation during accelerated aging. The diffusion-controlled t-m phase transformation initiated with the specimens sintered at 1450°C. This transformation was remarkable for the specimens sintered at 1600°C. X-ray photoelectron spectroscopy (XPS) measurements did not confirm the generation of Zr-OH and Y-OH bonds. No increase of yttrium concentration on the grain boundaries of Y-TZP was detected, which could be responsible for the destabilization of dental zirconia ceramics. A slight increase of diffusion-controlled t-m phase transformations was observed for all abraded specimens sintered at 1350 and 1450°C. The size of abrasive particles did not play a crucial role on LTD of Y-TZP. The retardation of diffusion-controlled t-m phase transformation was evident for all abraded specimens sintered at 1600°C by comparison to non-abraded specimens. CONCLUSION: The LTD of Y-TZP can be suppressed when the sintering temperature is set between 1350 and 1450°C.

Sampling gaseous oxidation products of aromatic compounds in gas/particle separation systems.

In this study we performed a direct comparison between two different ambient air samplers to characterize their performance in sampling oxidized gaseous organic compounds, known as oxidation products of aromatics. We investigated compounds with a variety of functional groups and vapor pressures. A polyurethane foam (PUF) adsorbent and an annular diffusion denuder sampler were operated along with particle filters. In both systems the sampling devices were liquid-extracted, followed by derivatization and analysis by GC-MS. The PUF system works very well for aromatic as well as non-aromatic compounds, whereas the denuder shows smaller collection efficiencies for highly volatile non-aromatic compounds. In addition, the sampling efficiencies in the PUF set-up are in good agreement with the calculated vapor pressures of the compounds and also the particle phase is not affected by most compounds.