Summary: This paper aims to discuss and review developments in plasma surface modification techniques which have been seen over the past few years, with particular emphasis on low energy or soft plasma assisted surface polymerisation processes. While early work focussed mainly on protective coatings and surface activation, the advancements in microtechnology in the 1980s followed by those in nanotechnology in the 1990s and 2000s have resulted in new challenges for surface processing and surface modification processes. The latest advancements in plasma polymer chemistry have shown tremendous potential for the synthesis of reasonably well defined molecular structures with a high retention of functional groups. Some of the latest achievements and newest insights into the behaviour of such deposits in a liquid environment will be discussed, with a particular focus on bio‐nanotechnological applications. Utilising novel approaches in surface and interface analysis, it will be shown that plasma polymers can be tailored to have considerable elasticity with reversible swelling characteristics, offering a three‐dimensional interface for biomolecular immobilisation procedures in a liquid environment.

Organic thin‐film transistors modified with 15‐base PNA strands are used for the selective detection of target DNA sequences. These simple devices provide a low‐cost, label‐free and in situ detection platform with excellent discrimination between single and double base mismatches in the target DNA sequence. The electronic detection signal is corroborated with conventional optical methods, displaying similar hybridization parameters.

Despite multiple research approaches to prevent bacterial colonization on surfaces, device‐associated infections are currently responsible for about 50% of nosocomial infections in Europe and significantly increase health care costs, which demands development of advanced antibacterial surface coatings. Here, novel antimicrobial composite materials incorporating zinc oxide nanoparticles (ZnO NP) into biocompatible poly(N‐isopropylacrylamide) (PNIPAAm) hydrogel layers are prepared by mixing the PNIPAAm prepolymer with ZnO NP, followed by spin‐coating and photocrosslinking. Scanning electron microscopy (SEM) characterization of the composite film morphology reveals a homogeneous distribution of the ZnO NP throughout the film for every applied NP/polymer ratio. The optical properties of the embedded NP are not affected by the matrix as confirmed by UV‐vis spectroscopy. The nanocomposite films exhibit bactericidal behavior towards Escherichia coli (E. coli) for a ZnO concentration as low as ≈0.74 μg cm−2 (1.33 mmol cm−3), which is determined by inductively coupled plasma optical emission spectrometry. In contrast, the coatings are found to be non‐cytotoxic towards a mammalian cell line (NIH/3T3) at bactericidal loadings of ZnO over an extended period of seven days. The differential toxicity of the ZnO/hydrogel nanocomposite thin films between bacterial and cellular species qualifies them as promising candidates for novel biomedical device coatings.

This review aims to provide a summary of some of the challenges in correlating surface science and biology, with particular emphasis on areas where plasma polymerization has and will play an important role as a method to synthesize reproducible and well-defined surfaces. Since the range of possible applications of plasma polymer films in biomaterial applications is immense, this paper will focus on processes to develop various surface morphologies and chemical structures for the immobilization of proteins and cells. Functional, plasma-polymerized films are discussed as biosensitive interfaces that may ultimately be part of a multilayer system that aims at connecting inorganic/metallic transducers with biologically reactive surfaces. These topics will be reviewed with some experimental results taken from the authors' own work. Specific aspects such as adhesion improvement and solvent effects are also discussed.

Plasma-assisted polymerization of maleic anhydride has been investigated under different experimental conditions. Significant variations in the film chemical structure and the film properties were obtained using pulsed plasma depositions operated at different duty cycles. The film chemical structures were obtained using X-ray photoelectron spectroscopy (XPS) and Fourier transform infra red spectroscopy (FT-IR). Surface derivatization reactions using decylamine and benzylamine were used to demonstrate their surface reactivity toward nucleophilic moieties and to change the surface free energy of the plasma polymer films, all of which are of particular interest for future applications in the attachment of biological molecules and cells. A method of substrate pretreatment was developed to ensure reliable binding between the substrate and the plasma polymer film in aqueous solution. Impedance spectroscopy was used to monitor polymer film changes in aqueous media. The hydrated films showed some resemblance to polyelectrolyte films and a clear correlation could be observed between the density of anhydride groups and the behavior of the films in solution.

This paper presents an investigation of allylamine polymerization in pulsed radio frequency (RF) plasma as an adhesion layer immobilizing DNA probe for DNA hybridization assay. We looked for a simple and innovative way to improve the stability of pulsed plasma polymerization allylamine (PPPAA) film in phosphate-buffered saline (PBS) solution. To better understand the mechanism of PPPAA stability and the influence on DNA adsorption from films, several techniques were used. Fourier transform infrared (FTIR), atomic force microscopy (AFM), surface contact angle, and surface plasmon resonance (SPR) as well as surface plasmon enhanced fluorescence spectroscopy (SPFS) were all employed to investigate the effect of plasma conditions on the film structure, amine density, and the DNA hybridization reaction. It concludes that polymer deposited at low working pressure is very stable and can be used as adhesion layers for further study of DNA hybridization assay.

The attachment of fibrinogen, bovine serum albumin, and immunoglobulin on continuous wave (CW) and pulsed plasma polymerized di(ethylene glycol) monovinyl ether was studied using surface plasmon resonance (SPR) spectroscopy and waveguide mode spectroscopy (WaMS). Structural analysis of the films was carried out using Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy. Plasma conditions employed during depositions produced significant differences in the chemical and physical properties of the resultant polymer films. Films deposited under CW and higher plasma duty cycles showed relatively high refractive indices (n > 1.57) and essentially a constant thickness if immersed in aqueous buffer solutions and exhibited a high adsorption affinity for proteins. In contrast, films produced under lower plasma duty cycles were of lower refractive index (n < 1.4), exhibited significant swelling if immersed in aqueous buffer, and were extremely effective in preventing protein adsorption. The SPR and WaMS data suggest that the relatively non-cross-linked films produced at the lower duty cycles exhibit hydrogel-like behavior when immersed in aqueous solutions. It is believed that these hydrated films are responsible for the remarkably effective nonfouling properties of the films deposited at low duty cycles. The relationship between film structure, polymer stability in aqueous buffer, and protein binding affinities are discussed.

Metallic nanostructures show interesting optical properties due to their plasmonic resonances, and when arranged in three-dimensional (3D) arrays hold promise for optical metamaterials with negative refractive index. Towards this goal a simple, cheap, and parallel method to fabricate large-area, ordered arrays of 150-nm gold nanocrescents supporting plasmonic resonances in the near-infrared spectral range is demonstrated. In this process hexagonally ordered monolayers of monodisperse colloids are prepared by a simple floating technique, and subsequently the individual particles are size-reduced in a plasma process and used as a shadow mask with the initial lattice spacing. The resulting two-dimensional array of plasmonic resonators is coated with a transparent silica layer, which serves as a support for a second layer prepared by the identical process. The mutual orientation of the nanostructures between the individual layers can be freely adjusted, which determines the polarization-dependent absorption of the array and opens the possibility to introduce chirality in this type of 3D metamaterial. The iteration of this simple and efficient methodology yields 3D arrays with optical features as sharp as those of the individual nanocrescents, and shows strong potential for large-scale production of high-quality optical metamaterials.