TOF-SIMS analysis of adipose tissue from patients with chronic kidney disease

In this work, time-of-flight secondary ion mass spectrometry (TOF-SIMS) was used for detecting systematic variations in the spatial and compositional distributions of lipids in human tissue samples. Freeze-dried sections of subcutaneous adipose tissue from six chronic kidney disease (CKD) patients and six control subjects were analysed by TOF-SIMS using 25 keV Bi₃⁺ primary ions. Principal component analysis of signal intensities from different fatty acids, diacylglycerol and triacylglycerol ions showed evidence for systematic variations in the lipid distributions between different samples. The main observed difference in the spectra was a concerted variation in the signal intensities from the saturated lipids relative to the unsaturated lipids, while variations in the fatty acid chain lengths were considerably weaker. Furthermore, the three samples showing the lowest degree of saturation came from CKD patients, while three of the four samples with the highest degree of saturation were from control subjects, indicating that low saturation levels in the glycerol lipid distribution may be more frequent in patients with CKD. Systematic differences in the spatial distributions between saturated and unsaturated glycerol lipids were observed in several analysed areas.     

An orientation analysis method for protein immobilized on quantum dot particles

The evaluation of orientation of biomolecules immobilized on nanodevices is crucial for the development of high performance devices. Such analysis requires ultra high sensitivity so as to be able to detect less than one molecular layer on a device. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) has sufficient sensitivity to evaluate the uppermost surface structure of a single molecular layer. The objective of this study is to develop an orientation analysis method for proteins immobilized on nanomaterials such as quantum dot particles, and to evaluate the orientation of streptavidin immobilized on quantum dot particles by means of TOF-SIMS. In order to detect fragment ions specific to the protein surface, a monoatomic primary ion source (Ga⁺) and a cluster ion source (Au₃⁺) were employed. Streptavidin-immobilized quantum dot particles were immobilized on aminosilanized ITO glass plates at amino groups by covalent bonding. The reference samples streptavidin directly immobilized on ITO plates were also prepared. All samples were dried with a freeze dryer before TOF-SIMS measurement. The positive secondary ion spectra of each sample were obtained using TOF-SIMS with Ga⁺ and Au₃⁺, respectively, and then they were compared so as to characterize each sample and detect the surface structure of the streptavidin immobilized with the biotin-immobilized quantum dots. The chemical structures of the upper surface of the streptavidin molecules immobilized on the quantum dot particles were evaluated with TOF-SIMS spectra analysis. The indicated surface side of the streptavidin molecules immobilized on the quantum dots includes the biotin binding site.     

Enhanced peptide molecular imaging using aqueous droplets

A new method in time-of-flight secondary ion mass spectrometry (ToF-SIMS) imaging, the droplet-enhanced method, was developed for the molecular analysis of biomaterials. To facilitate the ionization of biomolecules, a small amount of aqueous solution containing a variety of protonation agents as ionization-enhancing agents was dropped onto peptide samples before ToF-SIMS measurement. Using trifluoroacetic acid (TFA) as an enhancing agent, protonated insulin (MW 5733) ions were detected as not only [M + H]⁺ but also [M + 2H]²⁺ and [M + 3H]³⁺ from its film sample, using a Ga⁺ primary beam. TFA promoted the ionization of the large molecules much more effectively than did the other acids, and this peculiarity is related to both Na⁺ and Au₃⁺ intensities. We also demonstrated the visualization of dot-patterned insulin drawn with our bubble jet (BJ) printing technology using insulin molecular ion signals.     

Mutual information theory for biomedical applications: Estimation of three protein-adsorbed dialysis membranes

Protein-adsorbed dialysis membranes are evaluated with time-of-flight secondary ion mass spectrometry (TOF-SIMS) chemical imaging technique. Protein adsorption causing permeability change is one of big issues in the development of dialysis membranes. Bovine serum albumin adsorption onto three kinds of dialysis membranes has been evaluated with TOF-SIMS. In the present study three kinds of proteins, bovine serum albumin, α-chymotripsinogen A, and cytochrome C adsorbed onto hollow-fiber dialysis membranes, were measured by means of TOF-SIMS and then TOF-SIMS spectra were analyzed using mutual information. Then specific peaks of fragment ions related to α-chymotripsinogen A and bovine serum albumin were found, respectively. In this condition, however, specific peaks to cytochrome C were not able to find compared with other samples. Finally, chemical images of α-chymotripsinogen A and bovine serum albumin, respectively, adsorbed onto the membranes with co-existing proteins were obtained. The results of TOF-SIMS images of the proteins on the membranes show different tendency of adsorption depending on co-existing proteins. Further study is needed to study more detailed protein adsorption onto the membranes with co-existing proteins.     

Mass spectrometric characterization of DNA microarrays as a function of primary ion species

Recent studies have shown TOF-SIMS to be an appropriate method for the detailed examination of the immobilization process of PNA and its ability to hybridize to unlabeled complementary DNA fragments. Unlabeled single-stranded DNA was hybridized to Si wafer biosensor chips containing both complementary and non-complementary immobilized PNA sequences. The hybridization of complementary DNA could readily be identified by detecting phosphate-containing molecules from the DNA backbone. An unambiguous discrimination was achieved between complementary and non-complementary sequences.In order to optimize detection parameters, different primary ions were applied, including monoatomic ions (Bi⁺) as well as cluster ions (Bi₂⁺, Bi₃⁺, Bi₄⁺, Bi₃⁺⁺, Bi₅⁺⁺), and secondary ion yield behavior and formation efficiencies were studied. It was found that cluster primary ions resulted in a significantly increased yield of DNA-correlated fragments, enabling higher signal intensities and better secondary ion efficiencies.TOF-SIMS is undoubtedly a highly useful technique for identifying hybridized DNA on PNA biosensor chips. It is suitable for studying the complexity of the immobilization and hybridization processes and may provide a rapid method for DNA diagnostics. With the absence of the labeling procedure and the simultaneous increase of the phosphate signal as a result of increasing DNA sequence length, this technique comes to be especially useful for the direct analysis of genomic DNA.     

Improved quantitative analysis of Cu(In,Ga)Se2 thin films using MCs+-SIMS depth profiling

The chalcopyrite semiconductor, Cu(InGa)Se₂ (CIGS), is popular as an absorber material for incorporation in high-efficiency photovoltaic devices because it has an appropriate band gap and a high absorption coefficient. To improve the efficiency of solar cells, many research groups have studied the quantitative characterization of the CIGS absorber layers. In this study, a compositional analysis of a CIGS thin film was performed by depth profiling in secondary ion mass spectrometry (SIMS) with MCs⁺ (where M denotes an element from the CIGS sample) cluster ion detection, and the relative sensitivity factor of the cluster ion was calculated. The emission of MCs⁺ ions from CIGS absorber elements, such as Cu, In, Ga, and Se, under Cs⁺ ion bombardment was investigated using time-of-flight SIMS (TOF-SIMS) and magnetic sector SIMS. The detection of MCs⁺ ions suppressed the matrix effects of varying concentrations of constituent elements of the CIGS thin films. The atomic concentrations of the CIGS absorber layers from the MCs⁺-SIMS exhibited more accurate quantification compared to those of elemental SIMS and agreed with those of inductively coupled plasma atomic emission spectrometry. Both TOF-SIMS and magnetic sector SIMS depth profiles showed a similar MCs⁺ distribution for the CIGS thin films.     

TOF-SIMS 5 instrument sensitivity to matrix elements in GeSi Layers: Analysis based on recording of complex secondary ions

Ge _x Si_{1 − x} layers are investigated by means of secondary ion mass spectrometry (SIMS). Experimental results obtained with the use of a TOF-SIMS 5 instrument are presented. To surmount the so-called matrix effect, SIMS analysis is performed by using complex secondary ions: Ge₂⁻, CsGe⁺, and Cs₂Ge⁺.     

Comparison of secondary ion intensity enhancement from polymers on silicon and silver substrates by using Au-TOF-SIMS

The usefulness of the usage of cluster primary ion source together with an Ag substrate and detection of Ag cationized molecular ions was studied from the standpoint to realize high sensitivity TOF-SIMS analysis of organic materials. Although secondary ions from polymer thin films on a Si substrate can be detected in a higher sensitivity with Au₃⁺ cluster primary ion compared with Ga⁺ ion bombardment, it was clearly observed that the secondary ion intensities from samples on an Ag substrate showed quite a different tendency from that on Si. When monoatomic primary ions, e.g., Au⁺ and Ga⁺, were used for the measurement of the sample on an Ag substrate, [M+Ag]⁺ ions (M corresponds to polyethylene glycol molecule) were detected in a high sensitivity. On the contrary, when Au₃⁺ was used, no intensity enhancement of [M+Ag]⁺ ions was observed. The acceleration energy dependence of the detected secondary ions implies the different ionization mechanisms on the different substrates.     

Calculation of ion energy distributions of argon excimer ions generated in helicon plasma

A program is developed to calculate the ion energy distributions （IEDs） of Ar2^＋ making use of a simplified kinetic model with a combination of Monte Carlo method. Several coefficients are used to realize good match between the calculated and measured results. Some important assumptions are confirmed： argon excimer ions have short lifetime, hence they are formed in a short range before the collecting electrode. The excimer ions that encounter collisions will be discarded because they turn to other ion species after they collide with argon atoms. From the calculated results some plasma parameters such as the cross section or neutral density in discharge could be evaluated.     

High resolution surface imaging of Co/ZrO2 catalyst by TOF-SIMS

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) is a useful tool for the characterization of supported catalyst. Especially, the possibility of surface imaging appears very interesting. The images of not only elements distribution but also molecules or their fragments may be performed. Owing to the fast improvement of time-of-flight secondary ions mass spectrometers, obtaining the surface images with lateral resolution even below 100 nm is possible. The application of TOF-SIMS to the high resolution surface imaging of catalysts surfaces was shown. The influence of the preparation conditions of Co/ZrO₂ catalyst on the dispersion and composition of the active phase was investigated. The Co⁺/Zr⁺ and CoOH⁺/Zr⁺ intensity ratio values were calculated.     

On the information value of angular distributions in elastic scattering of heavy ions

A method is developed for computing the total cross section σ_F of complete and incomplete fusion, quasifission, and deep-inelastic collisions, as well as the total cross section σ_D of peripheral reactions, on the basis of analysis of angular distributions for elastic scattering of heavy ions. The method makes it possible, on a unified basis, to explain the mechanism of formation of σ_F and σ_D both for strongly and for weakly bound ions. The method permits the calculation of quantitative characteristics of fusion enhancement (and, accordingly, suppression of peripheral reactions) for strongly bound ions and, conversely, the suppression of fusion (and, accordingly, enhancement of peripheral reactions) for weakly bound ions. The potential of the method is demonstrated for two systems, ¹⁶O+²⁰⁸Pb and ⁹Be+²⁸Si, the projectile ion being strongly bound in the former system and weakly bound in the latter one.     

C60 sputtering of organics: A study using TOF-SIMS, XPS and nanoindentation

Sputtering of organic materials using a C₆₀ primary ion beam has been demonstrated to produce significantly less accumulated damage compared to sputtering with monatomic and atomic-cluster ion beams. However, much about the dynamics of C₆₀ sputtering remains to be understood. We introduce data regarding the dynamics of C₆₀ sputtering by evaluating TOF-SIMS depth profiles of bulk poly(methyl methacrylate) (PMMA). Bulk PMMA provides an ideal test matrix with which to probe C₆₀ sputter dynamics because there is a region of steady-state secondary ion yield followed by irreversible signal degradation. C₆₀ sputtering of PMMA is evaluated as a function of incident ion kinetic energy using 10 keV C₆₀⁺, 20 keV C₆₀⁺ and 40 keV C₆₀⁺⁺ primary ions. Changes in PMMA chemistry, carbon accumulation and graphitization, and topography as a function of total C₆₀ ion dose at each accelerating potential is addressed.     

TOF-SIMS analysis of magnetic materials in chum salmon head

A piece of tissue extracted from a chum salmon Oncorhynchus keta head was measured with time-of-flight secondary ion mass spectrometry (TOF-SIMS) in order to evaluate the distribution and composition of magnetic materials in the tissue, which may concern with geomagnetic navigation of long-distance migrating salmon. Several depositions of iron compounds were detected in the tissue by TOF-SIMS analysis. Comparing with total ion images providing a topological tissue structure, specific distribution of iron ion in the tissue was clearly shown. Higher magnification TOF-SIMS analysis revealed the existence of the aggregations of iron particles. Iron oxide clusters comprising many submicron particles were also detected in the tissue using scanning electron microscopy and X-ray analysis, suggesting the common existence of submicron-scale iron oxides in salmon heads. These results suggest that TOF-SIMS analysis is a valid method to clarify detailed structures and chemical properties of candidate magnetoreceptors in fish heads.     

Metal-assisted SIMS and cluster ion bombardment for ion yield enhancement

In addition to structural information, a detailed knowledge of the local chemical environment proves to be of ever greater importance, for example for the development of new types of materials as well as for specific modifications of surfaces and interfaces in multiple fields of materials science or various biomedical and chemical applications. But the ongoing miniaturization and therefore reduction of the amount of material available for analysis constitute a challenge to the detection limits of analytical methods. In the case of time-of-flight secondary ion mass spectrometry (TOF-SIMS), several methods of secondary ion yield enhancement have been proposed. This paper focuses on the investigation of the effects of two of these methods, metal-assisted SIMS and polyatomic primary ion bombardment. For this purpose, thicker layers of polystyrene (PS), both pristine and metallized with different amounts of gold, were analyzed using monoatomic (Ar⁺, Ga⁺, Xe⁺, Bi⁺) and polyatomic (SF₅⁺, Bi₃⁺, C₆₀⁺) primary ions. It was found that polyatomic ions generally induce a significant increase of the secondary ion yield. On the other hand, with gold deposition, a yield enhancement can only be detected for monoatomic ion bombardment.     

Two-dimensional observation of N2+ and N+ scattering patterns from Cu(001)

Low-energy (<1 keV) N₂⁺ and N⁺ ion scattering from the Cu(001) surface was directly observed by using a two-dimensional detection system. The two-dimensional pattern of the scattered ions changed when the primary ion energy was increased from 200 to 600 eV. The scattering peak shifted toward the [110] azimuth, to which the incident plane was not parallel, above 600 eV. The difference of ion-survival probabilities between N₂⁺ and N⁺ was discussed from the full width at half maximum of the angular distribution of scattered ions.     

Evaluation of secondary ion yield enhancement from polymer material by using TOF-SIMS equipped with a gold cluster ion source

We investigated the enhancement of the secondary ion intensity in the TOF-SIMS spectra obtained by Au⁺ and Au₃⁺ bombardment in comparison with Ga⁺ excitation using polymer samples with different molecular weight distributions. Since the polymer samples used in this experiment have a wide molecular weight distribution, the advantages of the gold cluster primary ion source over monoatomic ion could accurately be evaluated. It was observed that the degree of fragmentation decreased by the usage of cluster primary ion beam compared with monoatomic ion beam, which was observed as a shift of the intensity distribution in the spectra. It was also found out that the mass effect of Au⁺ and Ga⁺ as monoatomic primary ion, resulted in about 10-60 times of enhancement for both samples with different molecular distributions. On the other hand, the Au₃⁺ bombardment caused intensity enhancement about 100-2600 compared with Ga⁺ bombardment, depending on the mass range of the detected secondary ion species. The cluster primary ion effect of Au₃⁺, compared with Au⁺, therefore, was estimated to be about 10-45.     

TOF-SIMS structural characterization of self-assembly monolayer of cytochrome b5 onto gold substrate

Orientation and three-dimensional structure of immobilized proteins on bio-devices are very important to assure their high performance. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) is able to analyze upper surface of one layer of molecules. Orientation of immobilized proteins can be evaluated based on determination of a partial structure, representing ensemble of amino acids, on the surface part. In this study, a monolayer of cytochrome b5 was reconstituted onto gold substrate and investigated by surface plasmon resonance (SPR). After freeze-drying, the resulted protein self-assembly was evaluated using TOF-SIMS with the bismuth cluster ion source, and then TOF-SIMS spectra were analyzed to select peaks specific to cytochrome b5 and identify their chemical formula and ensembles of amino acids. The results from TOF-SIMS spectra analysis were compared to the amino acid sequence of the modified cytochrome b5 and three-dimensional structure of cytochrome b5 registered in the protein data bank. Finally, fragment-ion-generating parts of the immobilized-cytochrome b5 are determined based on the suggested residues and three-dimensional structure. These results suggest the actual structure and confirm the expected orientation of immobilized protein.     

Charge exchange cross sections of carbon ions

Based on experimental data on the ion charge distributions, the cross sections of single electron loss σ _{i, i + 1} and single electron capture σ _{i, i ? 1} by carbon ions with velocities (2.7–8) × 10⁸ cm/s in different gaseous media (He, N₂, and Ar) have been obtained. Regularities of the cross section variation of the electron capture and loss by carbon ions as a function of the ion velocity, ion charge, and atomic number of the target have been for the first time studied in a wide range of the initial ion charge, from i = 0 to i = 6. A qualitative agreement of the obtained results with the published data has been established for a number of other ions. Theoretical calculations of the cross sections of single electron loss by carbon ions in helium have been carried out.     

Analysis of TOF-SIMS spectra from fullerene compounds

We analyzed TOF-SIMS spectra obtained from three different size of fullerenes (C₆₀, C₇₀ and C₈₄) by using Ga⁺, Au⁺ and Au₃⁺ primary ion beams and investigated the fragmentation patterns, the enhancement of secondary ion yields and the restraint of fragmentation by using cluster primary ion beams compared with monoatomic primary ion beams. In the TOS-SIMS spectra from C₇₀ and C₈₄, it was found that a fragment ion, identified as C₆₀⁺ (m/z = 720), showed a relatively high intensity compared with that of other fragment ions related to C₂ depletion. It was also found that the Au₃⁺ bombardment caused intensity enhancement of intact molecules (C₆₀⁺, C₇₀⁺ and C₈₄⁺) and restrained the fragmentation due to C₂ depletion.     

The effect of angle of incidence to low damage sputtering of organic polymers using a C60 ion beam

The effect of angle of incidence of C₆₀ ion beam for low damage polymer depth profiling on TOF-SIMS and XPS has been investigated. In this study, TOF-SIMS and XPS depth profiles were taken at several angles of incidence of C₆₀ ion beam and the results were compared with each other. By using a higher angle of incidence, in XPS analysis, the changes of atomic concentration for polyethyleneterephthalate (PET) were suppressed. In TOF-SIMS analysis, the degradations of fragment ion intensity for PET and polystyrene (PS) were also suppressed at a higher angle of incidence. Although the information depth of TOF-SIMS is different from that of XPS, both results suggested that a higher angle of incidence is a better condition for low damage polymer depth profiling.