Research Emphasis

Thin Films Deposition

Plasma polymerized allylamine thin films have been deposited in CW RFGD reactor. The UV light-Ozone treatment of the substrate surface prior to deposition
seems to improve the adhesion and provide stable coating in aqueousmedia. The filmswere investigated using a large panel of spectroscopic, microscopic, and derivatization techniques, following the applied RF power. The results showa high dependence of the surface properties and layer composition on the plasma wattage, with a transition power around 50W. This suggests that the reactive functional groups density can be controlled by appropriate operational plasma parameters, especially input power. Hence, films with the desired amine concentration can be produced. The films presenting the best features for
biomedical applications are those deposited between 50 and 75W, which represents the transition power distinguishing two depositionmodes. In fact, these films display four important properties: (i) they are deposited at a high growth rate (26 nm/min), which allows the preparation of film thickness up to 800 nm; (ii) present a high primary amine content (5.5 NH2/ nm2) or 15 NH2 per 100 carbon atoms); (iii) show improved stability under water environment; and (iv) exhibit a good adhesion on different substrates and a good stability over time, with a constant water contact angle of around 608. In addition, AFM analysis shows a highly smooth and continuous film composed of nanometric hill-type clusters (1–2 nm). All over this work, the influence of the film thickness on the obtained results remains a recurring question. Furtherwork will clarify the contribution of the bulk structure on the measured parameters, especially the primary amine
density.

Surface Functionnalization for Biosensors and BioMEMS

Covalent attachment of trypsin on plasma polymerized allylamine

We have developped a successful immobilization protocol of trypsin on plasma polymerized allylamine films. In particular, we c onduct an interface analysis following the immobilization steps. All the characterization techniques used in this work (AFM, XPS, absorption spectroscopy) combinedwith the enzyme activity measurements by fluorescent spectroscopy converge to give conclusive proof of three main results: first, all the treated samples, without or with a GA linker display a complete surface coverage with a protein monolayer. This suggests that ppAA represents an interesting carrier for biomolecules immobilization, either by simple adsorpt ion or through covalent attachment. Secondly, the glutaraldehyde cross-linking does not change significantly the amount of bound
proteins on the polymer surface.Meanwhile it improves clearly the enzyme performance. Conversely, imino reduction treatment has no significant effect on enzyme activity, while it improves strongly the immobilization efficiency of the enzymes. Finally, it appears obvious that themost efficient immobilization protocol on plasma aminated films has to combine three crucial factors; i.e. the biocompatibility of the carrier, the accessibility and flexibility provided by GA crosslinking, with the stability rising from imino reduction. Such a process could generate immobilized biocatalysts surfaceswith a high operational stability, enabling thus
he accurate monitoring of the kinetic features.

Microfabrication and Microtechnology Processes

A novel fabrication method of closed microchannels for microfluidic systems is developped by our group. It is based on a direct plasma polymerization of the encapsulating material, here the organosilicon polymer ppTMDS, on a photopatterned resist. The latter, used as a sacrificial layer, was then decomposed to release the desired channels. We can easily create microchannels with various shapes and dimensions and with different surface features. In addition, this simple method allows the direct and rapid integration of fluidic circuits onto various sensors such as microelectrodes and waveguides. Applying the concept of plasma polymerization to the fluidic MEMS fabrication is particularly attractive for several reasons: (1) it avoids the bonding step in the fabrication protocol; (2) it uses the ambient temperature process; (3) the large panel of organic or organosilicon materials that can be deposited; (4) the good biocompatibility of these materials and their easy functionalization; (5) processing onto different material substrates without the need of an adhesion layer and (6) this process can be scaled up to industrial production relatively easily. Beside this, ppTMDS films enable the fabrication of very large cavities (>700 μm) without pillars and small channels (<5 μm width) without using a sacrificial material. One of our further challenges in this issue is the creation of microfluidic networks by the direct plasma polymerization of both sacrificial and overcoat layers to achieve the whole process in the same plasma reactor.

Plasma Study and Diagnostics