Plasma modified surfaces for covalent immobilization of functional biomolecules in the absence of chemical linkers: towards better biosensors and a new generation of medical implants

Abstract

Plasma modification and plasma polymer deposition are valuable technologies for the preparation of surfaces for the covalent binding of biomolecules for applications such as biosensors, medical prostheses, and diagnostic devices as well as surfaces for enzyme-mediated reactions. Covalency is conveniently tested by the ability of the surface to retain the attached molecules after vigorous washing with sodium dodecyl sulphate (SDS). Covalency is indicated if the fraction of protein retained lies above the curve characteristic of physisorption. Confidence in covalency is strengthened when the washing protocol is aggressive enough to remove all adsorbed protein from a control significantly more hydrophobic than the test surface. The use of linker chemistry to space the molecules from the surface is in some cases beneficial. However, the use of linker chemistry is not necessary to retain molecular function for long periods when the polymer surface is modified by energetic bombardment. The energetic bombardment retains hydrophilicity of the surface by crosslinking the subsurface, and this appears to facilitate retention of protein function. Energetic bombardment also increases the functional life of molecules immobilized and then freeze dried on plasma-modified surfaces. Analysis of the surfaces shows that the covalent binding mechanism is related to the presence of free radicals on the surface and in the subsurface regions. The unpaired electrons associated with the radicals appear to be mobile within the modified region and can diffuse to the surface to take part in binding interactions. Proactive implantable devices can make use of these principles of covalent attachment by seeding the surface of an implant with a biomolecule that elicits the desired interaction with cells and prevents undesirable responses.

Free radical functionalization of surfaces to prevent adverse responses to biomedical devices

“…1B shows it using an enzyme-linked immunosorbent assay (ELISA) to detect the presence of the protein. This technique is well-established in the literature as a method for testing for the covalency of macromolecular attachment and has been reviewed (15). SDS is an ionic surfactant that unfolds proteins and disrupts the forces responsible for physisorption, while leaving the covalent bonds intact.…”

“…An effective method of creating buried radicals is to treat an organic polymer with energetic ions (13,14). After treatment with energetic ions, either postformation or during their deposition, these surfaces strongly immobilize proteins (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29) and provide a means of cloaking biomaterial surfaces. What is required is a means of controlling the density of radicals to bind a full protein monolayer that is not compromised by excessive numbers of covalent bonds, while giving sufficient shelf life of the binding property for practical applications.…”

Ion-implanted polytetrafluoroethylene enhances Saccharomyces cerevisiae biofilm formation for improved immobilization

“…Compared with the untreated sample, the PIII-treated sample has new absorption lines at 1881 and 1723 cm 21 , corresponding to C¼O vibrations, and at 1657 cm 21 , corresponding to C¼C vibrations [16]. These peaks indicate that the PTFE surfaces were carbonized and oxidized as a result of PIII treatment.…”

Immobilization of superoxide dismutase/catalase onto polysulfone membranes to suppress hemodialysis-induced oxidative stress: A comparison of two immobilization methods

“…For this purpose, the enyzmes were immobilized onto plasma modified and polyethyleneimine (PEI) deposited polysulfone membranes. Plasma-based approaches have gained considerable interest for immobilization of biomolecules, since they do not require complicated wet chemical steps to achieve binding allowing linker-free immobilization [13]. Moreover, in some conditions lowered stability of bioactive molecules due to usage of spacers can be prevented [14].…”