Ambient DESI and LESA-MS analysis of proteins adsorbed to a biomaterial surface using in-situ surface tryptic digestion

The detection and identification of proteins adsorbed onto biomaterial surfaces under ambient conditions has significant experimental advantages but has proven to be difficult to achieve with conventional measuring technologies. In this study, we present an adaptation of desorption electrospray ionization (DESI) and liquid extraction surface analysis (LESA) mass spectrometry (MS) coupled with in-situ surface tryptic digestion to identify protein species from a biomaterial surface. Cytochrome c, myoglobin, and BSA in a combination of single and mixture spots were printed in an array format onto Permanox slides, followed by in-situ surface digestion and detection via MS. Automated tandem MS performed on surface peptides was able to identify the proteins via MASCOT. Limits of detection were determined for DESI-MS and a comparison of DESI and LESA-MS peptide spectra characteristics and sensitivity was made. DESI-MS images of the arrays were produced and analyzed with imaging multivariate analysis to automatically separate peptide peaks for each of the proteins within a mixture into distinct components. This is the first time that DESI and LESA-MS have been used for the in-situ detection of surface digested proteins on biomaterial surfaces and presents a promising proof of concept for the use of ambient MS in the rapid and automated analysis of surface proteins

The evolution of Pd/Sn catalytic surfaces in electroless copper deposition

This paper describes the different catalytic surfaces of Pd/Sn formed before electroless copper deposition onto a glass substrate. In this study, silanization of the glass surfaces with (3-aminopropyl) trimethoxysilane was used to provide a surface-coupled layer of functional molecules to assist in the adsorption of Pd/Sn catalyst and the subsequent copper deposition. The composition and microstructure of the modified glass surfaces were characterized by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry. These showed that catalytic Pd/Sn structures on the surface changed with increasing immersion time in the catalyst bath. The core-level XPS spectrum of Pd indicated that metallic Pd(0) became more significant in the catalyst layer than Pd(II) with the increasing immersion time. A model of the adsorption process is proposed to explain these changes. It was observed that too high a quantity of Pd(0) does not always improve the adhesion of the Cu deposits in the electroless process

Multivariate ToF-SIMS image analysis of polymer microarrays and protein adsorption

The complexity of hyperspectral time of flight secondary ion mass spectrometry (ToF-SIMS) datasets makes their subsequent analysis and interpretation challenging, and is often an impasse to the identification of trends and differences within large sample-sets. The application of multivariate data analysis has become a routine method to successfully deconvolute and analyze objectively these datasets. The advent of high-resolution large area ToF-SIMS imaging capability has enlarged further the data handling challenges. In this work, a modified multivariate curve resolution image analysis of a polymer microarray containing 70 different poly(meth)acrylate type spots (over a 9.2 × 9.2 mm area) is presented. This analysis distinguished key differences within the polymer library such as the differentiation between acrylate and methacrylate polymers and variance specific to side groups. Partial least squares (PLS) regression analysis was performed to identify correlations between the ToF-SIMS surface chemistry and the protein adsorption. PLS analysis identified a number of chemical moieties correlating with high or low protein adsorption, including ions derived from the polymer backbone and polyethylene glycol side-groups. The retrospective validation of the findings from the PLS analysis was also performed using the secondary ion images for those ions found to significantly contribute to high or low protein adsorption

Age-related changes to human stratum corneum lipids detected using time-of-flight secondary ion mass spectrometry following in vivo sampling

This work demonstrates the ability to detect changes in both quantity and spatial distribution of human stratum corneum (SC) lipids from samples collected in vivo. The SC functions as the predominant barrier to the body, protecting against the penetration of xenobiotic substances. Changes to the SC lipid composition have been associated with barrier impairment and consequent skin disorders and it is therefore important to monitor and quantify changes to this structure. This work demonstrates the first reported use of time of flight secondary ion mass spectrometry (ToF-SIMS) to assess physiological changes to human SC as a function of depth. This technique provides exceptional sensitivity and chemical specificity, al-lowing analysis of single tape stripped samples taken from volunteers. Using this methodology we were able to successfully identify chemical differences in human SC resulting from both intrinsic and extrinsic (photo) aging. Samples were collected from women of two age groups (under 27 and post-menopausal) and from two body sites with varying UV exposure (inner forearm and dorsal hand) and differences were identified using multivariate data analysis. The key finding was the signifi-cant aged-related increase and change in spatial distribution of the sterol cholesterol sulfate, a membrane stabilizing lipid. Significant changes in the prevalence of both lignoceric acid (C24:0) and hexacosanoic acid (C26:0) were also observed. This work describes previously unreported age-related chemical changes to human SC, providing an insight into aging mechanisms which may improve the design of both pharmaceutical and cosmetic topical products

Controlling the release of indomethacin from glass solutions layered with a rate controlling membrane using fluid-bed processing. Part 1: Surface and cross-sectional chemical analysis

Fluid bed coating has been shown to be a suitable manufacturing technique to formulate poorly soluble drugs in glass solutions. Layering inert carriers with a drug–polymer mixture enables these beads to be immediately filled into capsules, thus avoiding additional, potentially destabilizing, downstream processing. In this study, fluid bed coating is proposed for the production of controlled release dosage forms of glass solutions by applying a second, rate controlling membrane on top of the glass solution. Adding a second coating layer adds to the physical and chemical complexity of the drug delivery system, so a thorough understanding of the physical structure and phase behavior of the different coating layers is needed. This study aimed to investigate the surface and cross-sectional characteristics (employing scanning electron microscopy (SEM) and time of flight secondary ion mass spectrometry (ToF-SIMS)) of an indomethacin–polyvinylpyrrolidone (PVP) glass solution, top-coated with a release rate controlling membrane consisting of either ethyl cellulose or Eudragit RL. The implications of the addition of a pore former (PVP) and the coating medium (ethanol or water) were also considered. In addition, polymer miscibility and the phase analysis of the underlying glass solution were investigated. Significant differences in surface and cross-sectional topography of the different rate controlling membranes or the way they are applied (solution vs dispersion) were observed. These observations can be linked to the polymer miscibility differences. The presence of PVP was observed in all rate controlling membranes, even if it is not part of the coating solution. This could be attributed to residual powder presence in the coating chamber. The distribution of PVP among the sample surfaces depends on the concentration and the rate controlling polymer used. Differences can again be linked to polymer miscibility. Finally, it was shown that the underlying glass solution layer remains amorphous after coating of the rate controlling membrane, whether formed from an ethanol solution or an aqueous dispersion

Alkali incorporation into solution processed CIGS precursor layers

Solution based ion-exchange reactions offer a simple, non-vacuum route for adding Cu into In- Ga-Se precursor layers as a step in a low-cost process for the preparation of Cu(In, Ga)Se2 (CIGS) solar cells. The chemically treated precursor layers may be converted into CIGS by annealing with Se vapour. Structural and compositional characterisation has shown that the converted layers have good composition, microstructure and crystalline phase content. Nevertheless, photovoltaic cells processed from these layers have failed to produce energy conversion efficiencies greater than ~4% under standard test conditions. The chemical bath used for the incorporation of Cu into the precursor layers includes a complexant for stability and this complexant contains alkali atoms, which are known to strongly influence the properties of CIGS. Low alkali content is highly desirable in CIGS layers but excessive inclusion may be detrimental. This paper reports the results of an investigation into the potential incorporation of excess alkali atoms from the solution into the precursor layers. Whilst no evidence of alkali incorporation is detected by energy dispersive X-ray analysis, clear evidence is seen in time-of-flight secondary ion mass spectrometry measurements. The implications of this are discussed in terms of reported effects on device performance

Imaging of crystalline and amorphous surface regions using time-of-flight secondary-ion mass spectrometry (ToF-SIMS): application to pharmaceutical materials

The structure of a material, in particular the extremes of crystalline and amorphous forms, significantly impacts material performance in numerous sectors such as semiconductors, energy storage, and pharmaceutical products, which are investigated in this paper. To characterize the spatial distribution for crystalline−amorphous forms at the uppermost molecular surface layer, we performed time-of-flight secondary-ion mass spectroscopy (ToF-SIMS) measurements for quench-cooled amorphous and recrystallized samples of the drugs indomethacin, felodipine, and acetaminophen. Polarized light microscopy was used to localize crystallinity induced in the samples under controlled conditions. Principal component analysis was used to identify the subtle changes in the ToF-SIMS spectra indicative of the amorphous and crystalline forms for each drug. The indicators of amorphous and crystalline surfaces were common in type across the three drugs, and could be explained in general terms of crystal packing and intermolecular bonding, leading to intramolecular chain scission in the formation of secondary ions. Less intramolecular scission occurred in the amorphous form, resulting in a greater intensity of molecular and dimer secondary ions. To test the generality of amorphous−crystalline differentiation using ToF-SIMS, a different recrystallization method was investigated where acetaminophen single crystals were recrystallized from supersaturated solutions. The findings indicated that the ability to assign the crystalline/amorphous state of the sample using ToF-SIMS was insensitive to the recrystallization method. This demonstrates ToF-SIMS capabilities of detecting and mapping ordered crystalline and disordered amorphous molecular materials forms at micron spatial resolution in the uppermost surface of a material

Enhanced vitamin C skin permeation from supramolecular hydrogels, illustrated using in situ ToF-SIMS 3D chemical profiling

Vitamin C (ascorbic acid) is a naturally occurring, powerful anti-oxidant with the potential to deliver numerous benefits to the skin when applied topically. However, topical use of this compound is currently restricted by an instability in traditional formulations and the delivery and eventual fate of precursor compounds has been largely unexplored. Time of flight secondary ion mass spectrometry (ToF-SIMS) is an emerging technique in the field of skin research and offers detailed chemical analysis, with high mass and spatial resolution, as well as profiling capabilities that allow analysis as a function of sample depth. This work demonstrates the successful use of ToF-SIMS to obtain, in situ, accurate 3D permeation profiles of both ascorbic acid and a popular precursor, ascorbyl glucoside, from ex vivo porcine skin. The significant permeation enhancing effect of a supramolecular hydrogel formulation, produced from an amphiphilic gemini imidazolium-based surfactant, was also demonstrated for both compounds. Using ToF-SIMS, it was also possible to detect and track the breakdown of ascorbyl glucoside into ascorbic acid, elucidating the ability of the hydrogel formulation to preserve this important conversion until the targeted epidermal layer has been reached. This work demonstrates the potential of ToF-SIMS to provide 3D permeation profiles collected in situ from ex vivo tissue samples, offering detailed analysis on compound localisation and degradation. This type of analysis has significant advantages in the area of skin permeation, but can also be readily translated to other tissue types