Comparative Study of NAP-XPS and Cryo-XPS for the Investigation of Surface Chemistry of the Bacterial Cell-Envelope

Bacteria generally interact with the environment via processes involving their cell-envelope. Thus, techniques that may shed light on their surface chemistry are attractive tools for providing an understanding of bacterial interactions. One of these tools is Al Kα-excited photoelectron spectroscopy (XPS) with its estimated information depth of <10 nm. XPS-analyses of bacteria have been performed for several decades on freeze-dried specimens in order to be compatible with the vacuum in the analysis chamber of the spectrometer. A limitation of these studies has been that the freeze-drying method may collapse cell structure as well as introduce surface contaminants. However, recent developments in XPS allow for analysis of biological samples at near ambient pressure (NAP-XPS) or as frozen hydrated specimens (cryo-XPS) in vacuum. In this work, we have analyzed bacterial samples from a reference strain of the Gram-negative bacterium Pseudomonas fluorescens using both techniques. We compare the results obtained and, in general, observe good agreement between the two techniques. Furthermore, we discuss advantages and disadvantages with the two analysis approaches and the output data they provide. XPS reference data from the bacterial strain are provided, and we propose that planktonic cells of this strain (DSM 50090) are used as a reference material for surface chemical analysis of bacterial systems.

Profiling with Depth Resolution of Sub-nm for SiO2/ SiC Interface by Dual-Beam TOF-SIMS Combined with Simulation

For precise investigation of distribution for impurity or composition at SiO2/SiC interface, dual-beam Time-of-flight Secondary ion mass spectrometry (TOF-SIMS) with low energy sputtering beam was available. In addition to the experimental profiles, simulation using MRI model, in which Mixing, Roughness and Information depth were employed as parameters, enabled to acquire a more authentic distribution at the SiO2/SiC interface. Slight discrepancy on depth profiles between samples with different surface roughness was duplicated on the convoluted profiles in the simulation. Moreover, reconstructed profile of nitrogen indicated a real distribution with less impact of mixing and roughness, although that may contain uncertainty due to incompletion in the simulation model or variation of the distribution owing to detection species in the experiment. From the result of carbon profiles of both experimental and convoluted profiles, the relative discrepancy on the carbon distribution between samples was clarified, which suggested the possibility that a carbon thin layer at the SiO2/SiC interface would be found in the future.

DUAL MODALITY TRAN-ADMITTANCE MAMMOGRAPHY AND ULTRASOUND REFLECTION TO IMPROVE ACCURACY OF BREAST CANCER DETECTION

Cancer and breast tissue have a very high electrical impedance ratio, so imaging based on impedance can produce high contrast. It is very useful for the early detection of breast cancer. Trans-admittance mammography (TAM) is a modality to detect breast cancer based on impedance. The weakness of TAM is that it can only produce a projection image so that the volume and ratio of cancer to breast tissue cannot be obtained at once. The ratio of anomaly and volume is very important to be determined properly because it is related to the stage and type of cancer. TAM shortcomings can be overcome if anomalous volume information is known precisely. The ultrasound reflection modality can produce information about an anomaly depth and volume correctly. Combining TAM and ultrasound reflection data is expected to provide promising results. The study was conducted to prove the hypothesis by creating a breast phantom composed of gelatin, agar, graphite, glycerol, and distilled water to represent the electrical and acoustic physical properties of cancer and breast tissue. The results showed that the TAM data was only able to produce information about transverse position accurately, while the depth was less accurate. Acoustic devices can produce transverse position information, depth, and volume precisely. The dual-modality of TAM and ultrasound reflection can produce information about the depth position, volume, and the ratio anomaly to reference conductivity accurately.

Plastic fingerprint replica: solvent-assisted 3D molding and motion-promoted nano-spherulite formation

Fingerprinting is an essential form of identification for both biometric security and forensics today. Herein, we describe the procedure and principle of creating highly resolved, chemically robust, 3D fingerprint physical replicas, which is based on the solvent-assisted molding of transparent plastics and motion-promoted growth of semi-crystalline polymeric nanostructures. Prior to fingerprinting atop, polycarbonate, a commercial polymer with excellent durability and optical transparency, is first swelled and softened with a mild solvent (acetone). The molding motion conforms polymer chains between fingerprint ridges, which facilitates the formation of semi-crystalline spherulites and results in greater opacity between ridges than underneath ridges. Besides being more enduring than digital scanning and ink printed counterparts, the plastic fingerprint replicas can provide additional morphological information (depth of the ridge) and high-level details (distribution of sweat pores).