Modeling of RGDC film parameters using X-ray photoelectron spectroscopy

Current research progress of mammalian cell-based biosensors on the detection of foodborne pathogens and toxins

Foodborne diseases caused by pathogens and toxins are a serious threat to food safety and human health; thus, they are major concern to society. Existing conventional foodborne pathogen or toxin detection methods, including microbiological assay, nucleic acid-based assays, immunological assays, and instrumental analytical method, are time-consuming, labor-intensive and expensive. Because of the fast response and high sensitivity, cell-based biosensors are promising novel tools for food safety risk assessment and monitoring. This review focuses on the properties of mammalian cell-based biosensors and applications in the detection of foodborne pathogens (bacteria and viruses) and toxins (bacterial toxins, mycotoxins and marine toxins). We discuss mammalian cell adhesion and how it is involved in the establishment of 3D cell culture models for mammalian cell-based biosensors, as well as evaluate their limitations for commercialization and further development prospects.

Electroconductive polymeric nanowire templates facilitates in vitro C17.2 neural stem cell line adhesion, proliferation and differentiation

Stem cells still remain one of the most exciting and lucrative options for treatment of a variety of nervous system disorders and diseases. Although there are neural stem cells present in adults, the ability of both the peripheral and central nervous system for self-repair is limited at best. As such, there is a great need for a tissue engineering approach to solve nervous system disorders and diseases. In this study, we have developed electrically conductive surfaces with controlled arrays of high aspect ratio nanowires for the growth and maintenance of neural stem cells. The nanowire surfaces were fabricated from polycaprolactone using a novel nanotemplating technique, and were coated with an electrically conductive polymer, polypyrrole. The polypyrrole-coated nanowire surfaces were characterized using scanning electron microscopy and X-ray photoelectron spectroscopy. Additionally, the surface resistance of polypyrrole-coated nanowire surfaces was measured. C17.2 neural stem cells were used to evaluate the efficacy of the polypyrrole-coated nanowire surfaces to promote cell adhesion, proliferation and differentiation. The results presented here indicate significantly higher cellular adhesion and proliferation on polypyrrole-coated nanowire surfaces as compared to control surfaces. The differentiation potential of polypyrrole nanowire surfaces was also evaluated by immunostaining key neuronal markers that are expressed when NSCs differentiate into their respective neural lineages.

Molecular plasma deposited peptides on anodized nanotubular titanium: an osteoblast density study

A large amount of work is currently being conducted to design, fabricate, and characterize materials coated or immobilized with bioactive molecules for tissue engineering applications. Here, a novel method, molecular plasma deposition (MPD), is introduced with can efficiently coat materials with numerous bioactive peptides. Specifically, here, RGDS (arginine-glycine-aspartic acid-serine), KRSR (lysine-arginine-serine-arginine), and IKVAV (isoleucine-lysine-valine-alanine-valine) were coated on anodized nanotubular titanium using MPD. The anodized nanotubular titanium surfaces were characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), and water contact angle measurements. Peptide coatings were examined by X-ray photoelectron spectroscopy (XPS) and an amine reactive fluorescence molecule, 3-(4 carboxybenzoyl)quinoline 2-carboxaldehyde (CBQCA). Electrospray ionization (ESI) was used to confirm peptide integrity. Osteoblast (bone-forming cell) density was determined on the materials of interest. Results confirmed peptide coatings and showed that the MPD RGDS and KRSR coatings on anodized nanotubular titanium increased osteoblast density compared with uncoated substrates and those coated with IKVAV and a control peptide (RGES) after 4 h and 7 days. SEM confirmed differences in the morphology of the attached cells. These results, to the best of our knowledge, are the first reports using MPD to efficiently create peptide coatings to increase osteoblast density on metals commonly used in orthopedics. Since MPD represents a quick, inexpensive, and versatile technique to coat implants with peptides, it should be further studied for numerous implant applications.

Mixed adlayer of alkanethiol and peptide on GaAs(100): quantitative characterization by X-ray photoelectron spectroscopy

Homogeneous and mixed adlayers composed of an alkanethiol (1-octadecanethiol, ODT) and a peptide (CGISYGRKKRRQRRR) on GaAs(100) were formed in two different solvent systems: phosphate-buffered saline (PBS) and N,N-dimethylformamide (DMF). The chemical composition of each adlayer was characterized by X-ray photoelectron spectroscopy (XPS). The data showed that the makeup of the adlayer and its stability largely depends on the solvent used. Angle-resolved XPS also revealed that the adlayer thickness and tilt angles were different from values obtained from ellipsometry measurements and vastly varied between the two solvents used. The coverage data extracted from the XPS measurements indicated that homogeneous adlayers of peptide in PBS buffer form a multilayered film. Homogeneous alkanethiol adlayers exhibited monolayer coverage under all solvent treatments. Coadsorbed layers containing both alkanethiol and peptide have fractional monolayer coverage in both solvents.

Surface Analysis by X-ray Photoelectron Spectroscopy of Sol−Gel Silica Modified with Covalently Bound Peptides

Chemical surface characterization of biologically modified sol-gel derived silica is critical but somewhat limited. This work demonstrates the ability of x-ray photoelectron spectroscopy (XPS) to characterize the surface chemistry of peptide modified sol-gel thin films based on the example of four different free peptide-silanes, denoted RGD, NID, KDI ,and YIG. The N 1s and C 1s peaks were found to be good fingerprints of the peptides, whereas O 1s overlapped with the signal of substrate oxygen and, therefore, the O 1s peak was not informative in the case of the thin films. The C 1s peak was fitted and the contribution of the residual hydrocarbons was sorted out. The curve-fitting procedure of the C 1s peak accounted for the different chemical states of carbon atoms in the peptide structure. The curve-fitting procedure was validated by analyzing free peptides in the powder form and was then applied to the characterization of the peptide-modified thin films. The XPS measured ratio between nitrogen and carbon for the peptide thin film was similar to the corresponding value calculated from the peptide structures. Angle resolved XPS confirmed the surface nature of peptides in modified thin films. The coverage and thickness of the peptides on the thin film surface depended on the peptide sequence. The coverage was in the range of 10% of a monolayer, and the layer thickness varied from 10 to 30 A. We believe that the different thicknesses and surface coverage are due to the local structure of the peptides, with the RGD and NID peptides taking a globule conformation and the YIG and KDI peptides adopting a more linear structure.

Porous and Bioactive Alumina Ceramics for Bone Grafts and Tissue Engineering Scaffolds

An environmentally friendly direct foaming method was investigated to produce porous alumina ceramics. Egg white protein was used as a binder and foaming agent. The microstructures show that pores are interconnected with pore size of a few hundreds μm and pore window size of ca. 50 μm. The compressive strength of alumina foam is up to 100 MPa depending on porosity. Bioactivation of alumina was carried out using an alkaline solution treatment. Hydroxylation of alumina was achieved using 5M NaOH at 80°C for 4 days. In vitro assessments of the alumina in a human osteoblast cell-like cell (MG63) culture showed that the bioactivated alumina foams exhibited better cellularity and alkaline phosphatase (ALP) activity compared to untreated alumina foams. The results indicate that it is possible to improve the osseointgration of alumina ceramics by structural and surface modifications and to extend the applications of biocompatible alumina ceramics in biomedical implants and tissue engineering scaffolds.

Characterization of self-assembled organic films using differential charging in X-ray photoelectron spectroscopy

Differential charging is often regarded as a problem in X-ray photoelectron spectroscopic studies, especially for insulating or partially conducting samples. Application of a positive bias can reduce the effect of differential charging by attracting stray electrons from the system, thereby compensating for the electron loss. On the other hand, differential charging effect can be enhanced by the application of a negative bias to the sample during spectrum acquisition. The successful use of the differential charging technique to distinguish between multi- and monolayer organophosphonate films on oxide-covered silicon has been reported. A detailed description of this technique is now presented which shows how differential charging can be used as an important tool for the characterization of self-assembled films deposited on various surfaces. The dependence of this technique on the conductivity of the substrate has been investigated by studying the spectral behavior of the deposited films of phosphonic acid on conducting, semiconducting, and insulating samples (stainless steel, silicon, and glass). Application of either positive or negative dc electrical bias affects the carbon core-level (C1s) line shape and intensity, which is dependent on the atom's physical location above the surface.