Time of flight secondary ion mass spectrometry imaging of contaminant species in chemical vapour deposited graphene on copper

The human epidermal growth factor receptor 2 (HER2) specific radiotracer zirconium-Desferrioxamine(DFO)-trastuzumab was visualized ex-vivo by Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) imaging in ovarian and breast cancer xenograft tumor sections. Heterogeneous spatial distribution of [90Zr+] ions reflected the heterogeneous localization of trastuzumab, observed in parallel by immunohistochemistry staining in HER2+ tumors. Our results show that ToF-SIMS imaging is a quick and sensitive technique to image zirconium labelled biologics at microscale in tissues.

Time of flight secondary ion mass spectrometry (ToF-SIMS) is an ideal technique for the analysis of adsorbed protein films because of its surface sensitivity and chemical specificity. In this study, we examined ToF-SIMS with the multivariate calibration method partial least squares regression (PLSR) for the determination of the relative abundance of the components in binary protein films adsorbed onto mica, PTFE, and heptyl amine plasma polymer substrates. These results have been compared with independently measured 125I-radiolabeled protein adsorption experiments. By applying PLSR to the ToF-SIMS data, the relative abundance of the components in the binary adsorbed protein films was quantified, and the agreement between the ToF-SIMS and 125I-radiolabeling data was measured by the root mean square prediction error (RMSPE). Differences in protein quantification by PLSR and 125I-radiolabeling ranged from 5 to 25 mass % RMSPE and were highly dependent on the structure of the adsorbed protein film, the substrate surface chemistry and morphology, and the number of latent variables retained in the PLSR model. The limit of detection for the minor component in the adsorbed protein film was found to be approximately 10 mass %. This study demonstrates that the combination of ToF-SIMS and multivariate calibration provide complementary information to 125I-radiolabeling about the composition and structure of binary adsorbed protein films.

The cftr knockout mouse model of cystic fibrosis (CF) shows intestinal obstruction; malabsorption and inflammation; and a fatty acid imbalance in intestinal mucosa. We performed a lipid mapping of colon sections from CF and control (WT) mice by cluster time of flight secondary-ion mass spectrometry (TOF-SIMS) imaging to localize lipid alterations. Data were processed either manually or by multivariate statistical methods. TOF-SIMS analysis showed a particular localization for cholesteryl sulfate at the epithelial border, C16:1 fatty acid in Lieberkühn glands, and C18:0 fatty acid in lamina propria and submucosa. Significant increases in vitamin E (vE) and C16:0 fatty acid in the epithelial border of CF colon were detected. Principal component analysis (PCA) and partitioning clustering allowed us to characterize different structural regions of colonic mucosa according to variations in C14:0, C16:0, C16:1, C18:0, C18:1, C18:2, C20:3, C20:4, and C22:6 fatty acids; phosphatidylethanolamine, phosphatidylcholine, and phosphatidylinositol glycerolipids; cholesterol; vitamin E; and cholesteryl sulfate. PCA on spectra from Lieberkühn glands led to separation of CF and WT individuals. This study shows for the first time the spatial distribution of lipids in colonic mucosa and suggests TOF-SIMS plus multivariate analyses as a powerful tool to investigate disease-related tissue spatial lipid signatures.

A surface sensitive mass spectrometric technique: Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) was introduced to study the solid state instability of a methionine containing peptide caused by the oxidation of the methionine residue. The oxidation of a neuropeptide Methinonine-Enkephalin (ME) in air and under UV acceleration was studied by ToF-SIMS. The apparent oxidation rate is defined by the peak ratio of oxidized molecular ion over unoxidized molecular ion. ME is oxidized at a faster rate to its sulfoxide derivative in the UV accelerated oxidation environment than in lab air. The calibration curve for evaluating the ionization probability ratio of the oxidized deprotonated molecular ion divided by the unoxidized deprotonated molecular ion was obtained. This could be used to extract the real oxidation rate of ME in the solid state. The preliminary results showed that ToF-SIMS with simple sample handling, fast data acquisition, together with excellent surface sensitivity and detection limit could be an applicable and convenient tool to study peptide reactions in the solid state such as oxidation and deamidation process.

Using time of flight secondary ion mass spectrometry and field emission scanning electron microscopy with energy dispersive X-ray spectroscopy to determine the role of soil components in competitive copper and cadmium migration and fixation in soils

Characterization of biomaterial surfaces requires analytical techniques that are capable of detecting a wide concentration range of adsorbed protein. This range includes detection of low amounts of adsorbed protein (<10 ng/cm2) that may be present on non-fouling biomaterials. X-ray Photoelectron Spectroscopy (XPS) and Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) are surface sensitive techniques capable of detecting adsorbed proteins. We have investigated the lower limits of detection of both XPS and ToF-SIMS on four model substrates each presenting unique challenges for analysis by XPS and ToF-SIMS: mica, poly(tetrafluoroethylene), allyl amine plasma polymer and heptyl amine plasma polymer. The detection limit for XPS ranged from 10 ng/cm2 of fibrinogen (on mica) to 200 ng/cm2 (on allyl amine plasma polymers). The detection limit for ToF-SIMS ranged from 0.1 ng/cm2 of fibrinogen to 100 ng/cm2, depending on the substrate and data analysis. Optimal conditions provided detection limits between 0.1 ng/cm2 and 15 ng/cm2 on all of the substrates used in this study. While both techniques were shown to be effective in detecting protein, the sensitivity of both XPS and ToF-SIMS was shown to be dependent on substrate surface chemistry and the organization of the adsorbed protein film. This study specifically highlights the applicability of ToF-SIMS in the characterization of low level protein adsorption.

Combinatorial materials libraries are becoming more complicated; successful screening of these libraries requires the development of new high throughput screening methodologies. Time of flight secondary ion mass spectrometry (ToF-SIMS) is a surface analytical technique that is able to detect and image all elements (including hydrogen which is problematic for many other analysis instruments) and molecular fragments, with high mass resolution, during a single measurement. Commercial ToF-SIMS instruments can image 500 microm areas by rastering the primary ion beam over the region of interest. In this work, we will show that large area analysis can be performed, in one single measurement, by rastering the sample under the ion beam. We show that an entire 70 mm diameter wafer can be imaged in less than 90 min using ToF-SIMS stage (macro)rastering techniques. ToF-SIMS data sets contain a wealth of information since an entire high mass resolution mass spectrum is saved at each pixel in an ion image. Multivariate statistical analysis (MVSA) tools are being used in the ToF-SIMS community to assist with data interpretation; we will demonstrate that MVSA tools provide details that were not obtained using manual (univariate) analysis.

We present a methodology for the quantitative estimation of nitrogen in ultrathin oxynitrides by means of time of flight secondary ion mass spectrometry (TOF-SIMS) and x-ray photoelectron spectroscopy (XPS). We consider an innovative approach to TOF-SIMS depth profiling, by elemental distribution of single species as sum of peaks containing such species. This approach is very efficient in overcoming matrix effect arising when quantifying elements were distributed in silicon and silicon oxide. We use XPS to calibrate TOF-SIMS and to obtain quantitative information on nitrogen distribution in oxynitride thin layers. In the method we propose we process TOF-SIMS and XPS data simultaneously to obtain a quantitative depth profile.

Time of flight secondary ion mass spectrometry (TOF-SIMS) imaging has been used to investigate the incorporation of phospholipids into the plasma membrane of PC12 cells after incubation with phosphatidylcholine (PC) and phosphatidylethanolamine (PE). The incubations were done at concentrations previously shown to change the rate of exocytosis in model cell lines. The use of TOF-SIMS in combination with an in situ freeze fracture device enables the acquisition of ion images from the plasma membrane in single PC12 cells. By incubating cells with deuterated phospholipids and acquiring ion images at high mass resolution, specific deuterated fragment ions were used to monitor the incorporation of lipids into the plasma membrane. The concentration of incorporated phospholipids relative to the original concentration of PC was thus determined. The observed relative amounts of phospholipid accumulation in the membrane range from 0.5 to 2% following 19 h of incubation with PC at 100-300 μM and from 1 to 9% following incubation with PE at the same concentrations. Phospholipid accumulation is therefore shown to be dependent on the concentration in the surrounding media. In combination with previous exocytosis results, the present data suggests that very small changes in the plasma membrane phospholipid concentration are sufficient to produce significant effects on important cellular processes, such as exocytosis in PC12 cells.

Time of flight secondary ion mass spectrometry (ToFSIMS) of a number of hopanoids

Negative ion time of flight secondary ion mass spectrometry (ToF-SIMS) analysis of rigorously cleaned untreated, hydroxylamine and potassium hydroxide (KOH)-treated wool fabrics, produced with minimal finishing, has revealed the possible presence of hitherto unidentified bound acids at the surface of the wool fibre. Spectral peaks have been assigned to C8 through to C22 fatty acids, the odd numbered acids of which have been assigned to anteiso acids, (a), akin to the anteiso acid 18-methyleicosanoic acid known to be the dominant fatty acid bound to keratin fibre surfaces. This has included the assignment of some small peaks to hydroxylated aC18H36(OH)COS− and aC20H40(OH)COS− species, where the hydroxyl group is attached to the asymmetric 16 or 18 numbered carbon atom in the alkyl chain, respectively. The study has confirmed that many of the acids are bound to the fibre surface by thioester linkages (about 70%) and that the remainder is bound by oxygen ester acyl linkages. ToF-SIMS analysis of hydroxylamine-treated wool has confirmed the removal of all the thioester bound surface lipids, as well as lesser quantities but not all of the acyl bound lipids. In contrast, a 2 h KOH treatment removes all surface accessible bound lipids. Positive ion ToF-SIMS spectral analyses have not proved useful in characterising the possibly thiol rich fibre surface remaining after hydroxylamine treatment. The formation of characteristic immonium ions from surface cysteine residues after hydroxylamine treatment has been shown not to occur for free cysteine and so is unlikely to occur for such residues at the wool fibre surface. Scanning electron microscopy and transmission electron microscopy analyses have also been performed to assess the extent of the hydroxylamine reaction with the fibre. The implications of these findings for currently proposed models of the wool fibre surface, and for exploiting reactions of hydroxylamine followed by other electrophilic reagents to produce modified wool surfaces, are also discussed.

The use of many plastic packaging materials such as PVC, PAN, etc. to protect food and beverages is restricted because of toxicity and recycling problems and there is a need for the development of new packaging materials with good gas barrier properties. Plasma polymerized amorphous carbon hydrogen (a-C:H) films with a thickness of up to 100 nm are promising gas barriers for foodstuff applications when deposited on the outside of poly(ethyleneterephthalate) (PET) films. In order to understand the impact of the surface modification on permeability properties, a characterization method was developed using TOF-SIMS (time of flight secondary ion mass spectrometry) as the principal technique. The chemical and structural nature of plasma modified surfaces are characterized and related to the quality of a-C:H films on PET produced at EMPA (Swiss Federal Laboratories for Materials Testing and Research). In a first step, the mass peaks of TOF-SIMS spectra provided from the substrate materials PET and biopol® a biodegradable packaging material were identified and structural and/or total formulas were assigned. In the case of the biopol® substrate, the citroflex® plasticizer was detected on the polymer surface. Relative signal intensities were utilized to study the distribution of the two monomer units (valerate and butyrate) of biopol®. Principal component analysis (PCA) was used to reveal differences in relative signal intensities among TOF-SIMS spectra obtained from PET substrates provided by different suppliers and using different manufacturing processes. In some cases, the presence of acetaldehyde and surface pre-treatment from the manufacturer were established. In addition, the ion beam modification (dynamic SIMS mode) of the PET substrate material was studied to determine the static limit of TOF-SIMS measurements. In order to get insight into how the sputter process alters organic substrate materials during depth profiling, the decrease of molecular PET fragment intensities was studied. In a second step, existing structural and chemical SIMS parameters were applied and optimized to investigate TOF-SIMS spectra obtained from a-C:H films on PET. Molecular ion fragments (CxHyOz+) revealed a partially oxidized nature of the a-C:H films. In addition, the use of SIMS parameters combined with PCA analysis allowed to correlate poor gas barrier properties with a low degree of saturation (i.e. high aromaticitiy). Low mass and quasi molecular ions were used to identify the a-C:H/PET interface by dynamic TOF-SIMS depth profiling. AFM (Atomic Force Microscopy) and XPS (X-ray Photelectron Spectoscopy) were used as complementary methods to investigate the topography and the chemical composition of the a-C:H films on PET as well as of the substrate material. The partially oxidized nature of the a-C:H films was confirmed, the oxygen contents varying between 12-18%. A correlation between the oxygen content and the plasma treatment conditions of the substrate (application of a rf- or grounded-bias) was established, but no correlation with respect to gas permeability was found. Oxygen is believed to originate from post plasma reactions with air. ERDA (elastic recoil detection analysis) permitted to determine the bulk hydrogen content of the a-C:H films. However, the observed hydrogen content of 40% to 50% did not Vary significantly enough to be correlated to gas barrier properties. RBS (Rutherford Backscattering) allowed us to measure quantitative depth profiles of a-C:H carbon and revealed oxygen also inside of the a-C:H films. In addition, RBS measurements were useful to determine the areal densities of the a-C:H films on PET. The atom number density of the investigated a-C:H films varied between 0.19 and 0.24 g atom/cm3 and are similar to values found in the literature.

Raman spectroscopy and time of flight secondary ion mass spectrometry (ToF‐SIMS) were used to answer conservation questions left open after the preliminary analysis performed by the restoration team on the Bosch painting Saint Wilgefortis Triptych, within the project “Bosch in Venice.” In this work, we present the results obtained by combining these two techniques on five cross sections, concerning a detailed study of pigments and bindings degradation processes, the identification of organic components (binders/lakes), and the characterization of restoration products. Raman measurements show the presence of degradation products, such as calomel on the red pigment cinnabar, calcium‐oxalate, in particular weddellite, localized in a not original external layer, and finally lead soaps in several layers of the investigated samples. Although the detection of lead soaps suggests the use of oils as binders, Raman spectroscopy has given no conclusive information about such binders, neither on the possible presence of red lakes, suggested by independent UV observations. Complementary ToF‐SIMS investigations have instead revealed the presence of lead palmitate and stearate in the painting layers along with miristic, palmitic, oleic, and stearic acids, thus confirming the use of an oil medium, likely linseed oil. Additionally, ToF‐SIMS shows the presence of polydimethylsiloxane, likely from a previous restoration treatment in the 1990s, in the external layer of the investigated cross sections. Due to experimental difficulties during the analysis of the red lake, we can only hypothesize the presence of alizarin.

Time of flight secondary ion mass spectrometry (ToF-SIMS) is a useful technique in the study of adsorbed protein films because of its high surface sensitivity and chemical selectivity. However, the protein mass spectra generated by ToF-SIMS are complex fragmentation patterns of a polymer consisting of 20 different monomers (i.e., amino acids). Principal component analysis (PCA) was implemented to classify several reference positive ion protein spectra according to protein and substrate type. Furthermore, the positive ion 74/102 and 120/130 SIMS intensity ratios, radiolabeled experiments, and PCA were used to track the relative surface concentrations of bovine serum albumin and bovine fibronectin in a binary adsorption experiment. In all cases, the combination of ToF-SIMS and PCA proved capable in classifying proteins by their type (in the case of pure protein spectra) and relative surface concentration (in the case of the binary protein spectra).

Investigating the capability of ToF-SIMS to determine the oxidation state of Ce