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.     

The wettability of poly(tetrafluoroethylene) by aqueous solutions of ternary surfactant mixtures

Contact angle measurements on poly(tetrafluoroethylene) (PTFE) surface were carried out for the systems containing ternary mixtures of cetyltrimethylammonium bromide (CTAB) and p-(1,1,3,3-tetramethylbutyl)phenoxypoly(ethylene glycols), Triton X-100 (TX100) and Triton X-165 (TX165). The aqueous solution of ternary surfactant mixtures were prepared by adding the third surfactant to the binary mixture of the surfactants where the synergetic effect in the reduction of the surface tension of water was determined, to compare the influence of the third surfactants on the values of surface tension of this binary mixture and the values of the contact angle on PTFE. The obtained results and calculations indicate that the ternary mixtures of CTAB + TX165 (αCTAB = 0.2, γ_LV = 60 and 50 mN/m) + TX100 (C = 10⁻⁸ to 10⁻² M) have the biggest efficiency of the reduction of contact angle of water on PTFE in comparison to aqueous solutions of the single surfactants and their binary and ternary mixtures. Also in the case of all studied ternary mixtures of surfactants at concentrations of the bulk phase corresponding to unsaturated monolayer at water-air interface the adsorption of surfactants at PTFE-water interface is different than that at water-air interface, but is the same at concentrations near the critical micelle concentration (CMC). Thus the linear dependences between γ_LV cos θ − γ_LV and cos θ − 1/γ_LV, in the range of concentration studied for all systems confirm the same adsorption at two interfaces only at C near the CMC.     

The influence of the cholesterol microenvironment in tissue sections on molecular ionization efficiencies and distributions in ToF-SIMS

High-resolution images of cholesterol were obtained from Lymnaea stagnalis nervous tissue using metal-assisted (MetA) time-of-flight secondary ion mass spectrometry (ToF-SIMS). The spatial distributions of different pseudomolecular ions of cholesterol [M − H]⁺, [M − OH]⁺ and [2M + Au]⁺, illustrate the influence of the tissue microenvironment on the ionization efficiencies of these ions. These biological matrix effects result in differences in localizations of molecular ions derived from the same molecular species.     

Local chemical transformations in poly(dimethylsiloxane) by irradiation with 248 and 266 nm

Poly(dimethylsiloxane) (PDMS) has been irradiated with a frequency quadrupled Nd:YAG laser and a KrF^*-excimer laser at a repetition rate of 1 Hz. The analysis of ablation depth versus pulse number data reveals a pronounced incubation behavior. The thresholds of ablation (266 nm: 210 mJ cm⁻², 248 nm: 940 mJ cm⁻²) and the corresponding effective absorption coefficients α_eff (266 nm: 48900 cm⁻¹, 248 nm: 32700 cm⁻¹, α_lin = 2 cm⁻¹) were determined. The significant differences in the ablation thresholds for both irradiation wavelengths are probably due to the different pulse lengths of both lasers. Since the shorter pulse length yields a lower ablation threshold, the observed incubation can be due to a thermally induced and/or a multi-photon absorption processes of the material or impurities in the polymer.Incubation of polymers is normally related to changes of the chemical structure of the polymer. In the case of PDMS, incubation is associated with local chemical transformations up to several hundred micrometers below the polymer surface. It is possible to study these local chemical transformations by confocal Raman microscopy, because PDMS is transparent in the visible. The domains of transformation consist of carbon and silicon, as indicated by the appearance of the carbon D- and G-bands between 1310 and 1610 cm⁻¹, a band appearing between 502 and 520 cm⁻¹ can be assigned to mono- and/or polycrystalline silicon.The ablation products, which are detected in the surroundings of the ablation crater consist of carbon and amorphous SiO_x (x ≈ 1.5) as detected by infrared spectroscopy.     

Matrix-enhanced cluster-SIMS

We have used 23 keV C₆₀⁺ projectiles in the event-by-event bombardment and detection mode to investigate the emission of the gramicidin S [M − H]⁻ ion embedded in a matrix of sinapic acid. We have observed an increase in the gramicidin S [M − H]⁻ ion of approximately eight times by controlling the ratio of gramicidin S to sinapic acid. The maximum of the gramicidin S [M − H]⁻ yield occurs at a matrix/analyte ratio of 10:1. This ratio is different from those typically used in matrix-assisted laser desorption/ionization.     

Theoretical studies of the g factors and local structure for the rhombic Fe center in NaF

The anisotropic g factors and local structure for the rhombic Fe⁺ center in NaF are theoretically studied using the perturbation formulas of the g factors for a rhombically distorted octahedral 3d⁷ cluster. The impurity Fe⁺ is found not to occupy exactly the host Na⁺ site in NaF but to experience the off-center displacement of about 0.28 Å along [1 1 0] axis due to size mismatch substitution. The calculated g factors based on the above impurity displacement show reasonable agreement with the experimental data. The local structure of the Fe⁺ center is discussed.     

Study of a novel porous gel polymer electrolyte based on TPU/PVdF by electrospinning technique

Investigation on a new electrospun gel polymer electrolyte consisting of thermoplastic polyurethane (TPU) and poly(vinylidene fluoride) (PVdF) has been made. Its characteristics were investigated by scanning electron microscopy, FT-IR, Differential Scanning Calorimeter (DSC) analysis. This kind of gel polymer electrolyte had a high ionic conductivity about 3.2 × 10^− 3 S cm^− 1 at room temperature, and exhibited a high electrochemical stability up to 5.0 V versus Li⁺/Li, good mechanical strength and stability to allow safe operation in rechargeable lithium-ion polymer batteries. A Li/GPE/LiFePO₄ cell delivered a high discharge capacity when it was evaluated at 0.1 °C—rate at 25 °C (167.8 mAh g^− 1). And a very stable cycle performance also existed under this low current density.     

Synthesis, characterization and spectroscopic investigation of new tetrakis(acetylacetonato)thulate(III) complexes containing alkaline metals as countercations

In this work a series of tetrakis complexes C[Tm(acac)₄], where C⁺=Li⁺, Na⁺ and K⁺ countercations and acac=acetylacetonate ligand, were synthesized and characterized for photoluminescence investigation. The relevant aspect is that these complexes are water-free in the first coordination sphere. The emission spectra of the tetrakis Tm³⁺-complexes present narrow bands characteristic of the ¹G₄→³H₆ (479 nm), ¹G₄→³F₄ (650 nm) and ¹G₄→³H₅ (779 nm) transitions of the Tm³⁺ ion, with the blue emission color at 479 nm as the most prominent one. The lifetime values (τ) of the emitting ¹G₄ level of the C[Tm(acac)₄] complexes were 344, 360 and 400 ns for the Li⁺, Na⁺ and K⁺ countercations, respectively, showing an increasing linear behavior versus the ionic radius of the alkaline ion. An efficient intramolecular energy transfer process from the triplet state (T) of the ligands to the emitting ¹G₄ state of the Tm³⁺ ion is observed. This fact, together with the absence of water molecules in first coordination sphere, allows these tetrakis Tm³⁺-complexes to act as efficient blue light conversion molecular devices.     

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.     

Studies on poly(vinylidene fluoride-co-hexafluoropropylene) based gel electrolyte nanocomposite for sodium-sulfur batteries

Experimental investigations on a sodium ion conducting gel polymer electrolyte nanocomposite based on poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP), dispersed with silica nanoparticles are reported. The gel nanocomposites have been obtained in the form of dimensionally stable, transparent and free-standing thick films. Physical characterization by X-ray diffraction (XRD), Fourier transform Infra-red (FTIR) spectroscopy and Scanning electron microscopy (SEM) have been performed to study the structural changes and the ion-filler-polymer interactions due to the dispersion of SiO₂ nanoparticles in gel electrolytes. The highest ionic conductivity of the electrolyte has been observed to be 4.1 × 10⁻³ S cm^− 1 at room temperature with ~ 3 wt.% of SiO₂ particles. The temperature dependence of the ionic conductivity has been found to be consistent with Vogel-Tammen-Fulcher (VTF) relationship in the temperature range from 40 to 70 °C. The sodium ion conduction in the gel electrolyte film is confirmed from the cyclic voltammetry, impedance analysis and transport number measurements. The value of sodium ion transport number (t_Na+) of the gel electrolyte is significantly enhanced to a maximum value of 0.52 on the 15 wt.% SiO₂ dispersion. The physical and electrochemical analyses indicate the suitability of the gel electrolyte films in the sodium batteries. A prototype sodium-sulfur battery, fabricated using optimized gel electrolyte, offers the first discharge capacity of ~165 mAh g^− 1 of sulfur.     

Multi-responsive poly(N-isopropylacrylamide) hydrogel with D-π-A type dye

To get a multi-responsive polymer hydrogel, metal sensible and acid/base-switchable D-π-A type dye monomer was synthesized first. The synthesized electron donor-π-conjugated-electron acceptor (D-π-A) type dye monomer 3 was investigated with not only the selective Ni²⁺ and Cu²⁺ metal ion sensing effects, but also an acid/base unit sensing effects in optical properties with UV-vis absorption and fluorescence emission. A thermo-responsive poly(NIPAM-co-dye) copolymer with D-π-A type dye was prepared by typical radical copolymerization. The LCST behavior was investigated by UV-vis spectroscopy, which allows the measurement of the phase transition from 20 to 50 °C in an aqueous solution. The poly(NIPAM-co-dye) copolymer also exhibited color change when not only Ni²⁺ or Cu²⁺ cations were used but also when an acid/base unit was used. The morphology of the internal matrix structure of the poly(NIPAM-co-dye) hydrogel was observed by SEM.     

Thiolated cyclodextrin self-assembled monolayer-like characterized with secondary ion mass spectrometry

In the work the focus is on the preparation of self-assembled monolayer-like films consisting of thiolated cyclodextrin on gold substrate and a characterization by using secondary ion mass spectrometry. The short (1 min) and long (1 h) time preparations of self-assembled monolayer-like films, resulting in submonolayer and monolayer regimes, are investigated, respectively. The observed species of thiolated cyclodextrin (M as molecular ion) self-assembled monolayer-like films are assigned to three groups: Au_xH_yS_z clusters, fragments with origin in cyclodextrin molecule associated with Au, and molecular ions. The group of Au_xH_yS_z (x = 2-17, y = 0-2, z = 1-5) clusters have higher intensities than other species in the positive and even more in negative mass spectra. Interestingly, the dependence between the number of Au and S atoms shows that with the increasing size of Au_xH_yS_z clusters up to 11 Au atoms, the number of associated S atoms is also increasing and then decreasing. Molecular species as (M−S+H)Na⁺, (M+H)Na⁺, AuMNa⁺, (M₂−S)Na⁺, and M₂Na⁺ are determined, and also in cationized forms with K⁺. The intensities of thiolated cyclodextrin fragments at the long time preparation are approximately 10 times higher than the intensities of the same fragments observed at the short time. The largest observed ions in thiolated cyclodextrin self-assembled monolayer-like films are AuM₂ and Au₂M. The thiolated cyclodextrin molecular ions are compared with hexadecanethiol molecular ions in the form of Au_xM_w where the values of x and w are smaller for thiolated cyclodextrin than for hexadecanethiol. This result is supported with larger, more compact, and more stabile thiolated cyclodextrin molecule.     

Biodegradable nanocomposite magnetite stent for implant-assisted magnetic drug targeting

This study shows, for the first time, the fabrication of a biodegradable polymer nanocomposite magnetic stent and the feasibility of its use in implant-assisted-magnetic drug targeting (IA-MDT). The nanocomposite magnetic stent was made from PLGA, a biodegradable copolymer, and iron oxide nanopowder via melt mixing and extrusion into fibers. Degradation and dynamic mechanical thermal analyses showed that the addition of the iron oxide nanopowder increased the polymer’s glass transition temperature (T_g) and its modulus but had no notable effect on its degradation rate in PBS buffer solution. IA-MDT in vitro experiments were carried out with the nanocomposite magnetic fiber molded into a stent coil. These stent prototypes were used in the presence of a homogeneous magnetic field of 0.3 T to capture 100 nm magnetic drug carrier particles (MDCPs) from an aqueous solution. Increasing the amount of magnetite in the stent nanocomposite (0, 10 and 40 w/w%) resulted in an increase in the MDCP capture efficiency (CE). Reducing the MDCP concentrations (0.75 and 1.5 mg/mL) in the flowing fluid and increasing the fluid velocities (20 and 40 mL/min) both resulted in decrease in the MDCP CE. These results show that the particle capture performance of PLGA-based, magnetic nanocomposite stents are similar to those exhibited by a variety of different non-polymeric magnetic stent materials studied previously.     

Enhancement effect in photon-stimulated ion desorption for benzene adsorbed on silicon surfaces observed using angle-dependent technique

We have investigated photon-stimulated ion desorption from deuterated benzene (C₆D₆) adsorbed on Si(1 0 0) and Si(1 1 1) surfaces following C 1s core excitation. Using time-of-flight mass spectrometry combined with angle-dependent technique, we measured the dependences of mass-spectra of desorption ions on photon energies and on incident angle (θ) of synchrotron beam. We have found the ion yields for adsorbate-derived fragments of CD⁺ and CD₂⁺ are enhanced in very small angles of incident X-rays. Moreover, molecular orientation effect appeared in excitation energy dependences of D⁺ ions from the Si(1 0 0) and Si(1 1 1) surfaces; that is, ion yield spectra measured at θ = 10° are different from that at θ = 65°. Furthermore, it was found that desorption ion yields increase greatly with decreasing incident angles. The angular dependences are consistently similar for all ion species, excitation energies, and indexes of substrates. Possible desorption processes are described on the basis of the observations.     

Study of S ion-assisted sulfurization of n-GaAs (1 0 0) surface

The chemical structure and site location of sulfur atoms on n-GaAs (1 0 0) surface treated by bombardment of S⁺ ions over their energy range from 10 to 100 eV have been studied by X-ray photoelectron spectroscopy and low energy electron diffraction. The formation of Ga-S and As-S species on the S⁺ ion bombarded n-GaAs surface is observed. An apparent donor doping effect is observed for the n-GaAs by the 100 eV S⁺ ion bombardment. It is found that the S⁺ ions with higher energy are more effective in the formation of Ga-S species, which assists the n-GaAs (1 0 0) surface in reconstruction into an ordered (1 × 1) structure upon subsequent annealing. The treatment is further extended to repair Ar⁺ ion damaged n-GaAs (1 0 0) surface. It is found that after a n-GaAs (1 0 0) sample is damaged by 150 eV Ar⁺ ion bombardment, and followed by 50 eV S⁺ ion treatment and subsequent annealing process, finally an (1 × 1) ordering GaAs (1 0 0) surface with low surface states is obtained.     

Charge exchange between low energy alkali ions and cerium oxide surfaces

The fraction of low energy Na⁺ ions neutralized during single scattering from CeO₂(1 0 0) surfaces was measured with time-of-flight spectroscopy. The projectile ionization level is resonant with the surface electronic states, so that the neutralization results from a non-adiabatic charge exchange process that depends on the exit velocity and the local electrostatic potential (LEP) along the exit trajectory at a point close to the surface. Variations of the measured neutral fraction with ion energy and exit angle differ from the results obtained from clean metals due to the inhomogeneity of the LEP on an oxide surface. The results suggest that neutral fraction data collected as a function of emission angle and ion energy could be used to quantitatively map the shape of an inhomogeneous LEP.     

Fluorescence quenching of 6-methoxyquinoline: an indicator for sensing chloride ion in aqueous media

The quenching of fluorescence intensity and decay time of protonated form of 6-methoxyquinoline (6MQ⁺) with chloride ion (Cl⁻) in aqueous solution at ambient temperatures have been investigated. The quenching follows linear Stern-Volmer relation. The values of Stern-Volmer quenching constant/quenching efficiency (K_sv) and quenching rate constant (K_q) for the Cl⁻ ion are close to 75 M⁻¹ and 3.21×10⁹ M⁻¹ S⁻¹, respectively. The quenching is found to be collisional or dynamical in nature. The study reveals that the system can be used as a sensor for the detection of chloride ion.     

Depth profiling of taxol-loaded poly(styrene-b-isobutylene-b-styrene) using Ga and C60 ion beams

The surface of a triblock copolymer, containing a solid-phase drug, was investigated using 15 keV Ga⁺ and 20 keV C₆₀⁺ ion beams. Overall, the results illustrate the successful use of a cluster ion beam for greatly enhancing the molecular ion and high-mass fragment ion intensities from the surface and bulk of the polymer system. The use of C₆₀⁺ also established the ability to see through common overlayers like poly(dimethyl siloxane) which was not possible using atomic ion sources. Moreover, the use of C₆₀⁺ allowed depth profiles to be obtained using primary ion dose densities in excess of 6 × 10¹⁴ C₆₀⁺/cm². Resulting sputter craters possess relatively flat bottoms without the need for sample rotation and reached depths of ca. 2 μm. AFM results illustrate the more gentile removal of surface species using cluster ions. Specifically, phase contrast and topographic images suggest the relatively high ion doses do not significantly alter the phase distribution or surface topography of the polymer. However, a slight increase in rms roughness was noticed.     

Fourier transform emission spectroscopy of the BΣ-XΣ system of CN

The emission spectrum of the B²Σ⁺-X²Σ⁺ system of CN has been observed at high-resolution using a Fourier transform spectrometer. The rotational structure of a large number of bands involving vibrational levels v = 0-15 of both electronic states has been analyzed, and improved spectroscopic constants have been determined by combining the microwave and infrared measurements from previous studies. Improved spectroscopic constants for vibrational levels up to v″ = 18 in the X²Σ⁺ state and v′ = 19 in the B²Σ⁺ state have been determined by combining the measurements of the 16-13, 18-17, 18-18, 19-15, and 19-18 bands of Douglas and Routly [Astrophys. J. Suppl. 1 (1955) 295-318] and 17-14 and 17-16 bands of Ito et al. [J. Chem. Phys. 96 (1992) 4195] with our data. The band constants obtained have been used to estimate equilibrium ground state constants for CN.     

Photoluminescence and optical properties of He ion bombarded ultra-high molecular weight polyethylene

Ion bombardment is a suitable tool to improve the physical and chemical properties of polymer surface. In this study UHMWPE samples were bombarded with 130 keV He ions to the fluences ranging from 1 × 10¹² to 1 × 10¹⁶ cm⁻². The untreated and ion beam modified samples were investigated by photoluminescence, and ultraviolet-visible (UV-vis) spectroscopy. Remarkable decrease in integrated luminescence intensity with increasing ion fluences was observed. The reduction in PL intensity with increase of ion fluence might be attributed to degradation of polymer surface and formation of defects. The effect of ion fluence on the optical properties of the bombarded surfaces was characterized. The values of the optical band gap E_g, and activation energy E_a were determined from the optical absorption. The width of the tail of the localized states in the band gap (E_a) was evaluated using the Urbach edge method. With increasing ion fluences a decrease in both the energy gap and the activation energy were observed. Increase in the numbers of carbon atoms (N) in a formed cluster with increasing the He ion fluence was observed.