Controlled covalent surface immobilisation of proteins and peptides using plasma methods

Coated layers of biologically active molecules on synthetic biomaterials and biomedical devices can promote a variety of desirable biological reactions by the host body or the biological medium, such as cell and tissue attachment or deterring bacterial biofilm formation. Such coated layers should be immobilised covalently in order to avoid competitive displacement phenomena, and the use of surface-activating plasmas or plasma polymer interlayers with suitable chemical surface groups has proved to be very convenient means of grafting bioactive molecules onto solid materials surfaces. We review selected work on the covalent immobilisation of proteins and peptides onto solid biomaterial surfaces and describe efforts towards plasma methods that allow biomolecules to be covalently captured in a single step. After reviewing a number of approaches, we discuss in more detail the use of plasma polymer interlayers that possess aldehyde or epoxide surface groups; these groups react readily with amine groups on proteins and peptides without undesirable side reactions, and avoid other issues such as crosslinking. We also emphasise the importance of detailed surface analysis to verify that covalent grafting has indeed taken place, and to assess the surface density of grafted molecules. With suitably chosen peptides or proteins, such covalently grafted layers can support the surface attachment of delicate cells, or combat bacterial biofilm formation.

Optical biosensing for label-free cellular studies

Optical biosensors such as waveguides and surface-plasmon resonance (SPR) sensors have found numerous applications in biomolecular sciences. We provide an overview of these technologies in relation to the specific requirements of label-free and high-throughput cellular studies. We dedicate specific emphasis to SPR-based biosensors and recent developments particularly suitable for cellular studies, such as long-range SPR. We discuss the advantages and the disadvantages of the most successful optical-sensing technologies, and potential approaches in the next generation of optical technologies.

Substrate influence on the initial growth phase of plasma-deposited polymer films

In this communication we demonstrate that in the initial stages of deposition of ultrathin plasma polymer films, both the growth rate and the chemical composition of the films are affected by the nature of the substrate which is an important question surprisingly neglected until now.

Platforms for controlled release of antibacterial agents facilitated by plasma polymerization

Bacterial infections present an enormous problem causing human suffering and cost burdens to the healthcare systems worldwide. Herein we present several versatile strategies for controlled release of antibacterial agents which include silver ions as well as traditional antibiotics. At the heart of these release platforms is a thin film deposited by plasma polymerization. The use of plasma polymerization makes these strategies applicable to the surface of many types of medical devices since the technique for deposition of a polymer film from plasma in practically substrate independent.

Molecular-level removal of proteinaceous contamination from model surfaces and biomedical device materials by air plasma treatment

Established methods for cleaning and sterilising biomedical devices may achieve removal of bioburden only at the macroscopic level while leaving behind molecular levels of contamination (mainly proteinaceous). This is of particular concern if the residue might contain prions. We investigated at the molecular level the removal of model and real-life proteinaceous contamination from model and practical surfaces by air plasma (ionised air) treatment. The surface-sensitive technique of X-ray photoelectron spectroscopy (XPS) was used to assess the removal of proteinaceous contamination, with the nitrogen (N1s) photoelectron signal as its marker. Model proteinaceous contamination (bovine serum albumin) adsorbed on to a model surface (silicon wafer) and the residual proteinaceous contamination resulting from incubating surgical stainless steel (a practical biomaterial) in whole human blood exhibited strong N1s signals [16.8 and 18.5 atomic percent (at.%), respectively] after thorough washing. After 5 min air plasma treatment, XPS detected no nitrogen on the sample surfaces, indicating complete removal of proteinaceous contamination, down to the estimated XPS detection limit 10 ng/cm2. Applying the same plasma treatment, the 7.7 at.% nitrogen observed on a clinically cleaned dental bur was reduced to a level reflective of new, as-received burs. Contact angle measurements and atomic force microscopy also indicated complete molecular-level removal of the proteinaceous contamination upon air plasma treatment. This study demonstrates the effectiveness of air plasma treatment for removing proteinaceous contamination from both model and practical surfaces and offers a method for ensuring that no molecular residual contamination such as prions is transferred upon re-use of surgical and dental instruments.

Tuneable and robust long range surface plasmon resonance for biosensing applications

A multilayered biosensing architecture based on long range surface plasmons (LRSPs) is reported. LRSPs originate from the coupling of surface plasmons on the opposite sides of a thin metal film embedded in a symmetrical refractive index environment. With respect to regular SPs, LRSPs are characterized by extended electromagnetic field profiles and lower losses, making them of high interest in biosensing, especially for large biological entities. LRSPs-supporting layer structures are typically prepared by using fluoropolymers with refractive indices close to that of water. Unfortunately, fluoropolymers have low surface energies which can translate into poor adhesion to substrates and sub-optimal properties of coatings with surface plasmon resonance-active metal layers such as gold. In this work, a multilayered fluoropolymer structure with tuneable average refractive index is described and used to adjust the penetration depth of LRSP from the sensor surface. The proposed methodology also provides a simple solution to increase the adhesion of LRSP-supporting structures to glass substrates. Towards taking full advantage of long range surface plasmon resonance sensors, a novel approach based on the plasma-polymerization of allylamine is also described to improve the quality of gold layers on fluoropolymers such as Teflon AF.