Tetraethyl orthosilicate and acrylic acid forming robust carboxylic functionalities on plastic surfaces for biodiagnostics

Surface functionalisation and effects related to non-specific binding of the detection molecules are the key aspects to be considered for fluorescence-linked bioassays. Here, we present a deposition of polymeric structures with carboxylic acid functionalities by plasma enhanced chemical vapour deposition. We report on characterisation and some unique properties of the film formed as a result of sequential, plasma assisted fragmentation and deposition from vapours of acrylic acid (AA) and tetraethyl orthosilicate (TEOS). TEOS serves as an adhesion layer to the plastic substrate and also as a network building layer for further cross-linking with AA, the sequential plasma deposition resulting in a film of composition graded from inside to outside. The presence of silanols (Si-OH) can facilitate large uptake of water molecules and cause significant hydration of the layer, which in combination with high total negative charge lowers the non-specific binding of biomolecules. Furthermore, the specific combination of TEOS and AA significantly increased the proportion of carboxyl groups in the layer, above that found from deposition of AA alone. The availability and reactivity of the carboxyl functionalities for covalent attachment of specific bioreceptor molecules was confirmed by a total internal reflection ellipsometry technique in a reaction with amino terminated ssDNA. The combination of low non-specific binding and high specific binding amount gave a high signal/noise ratio. Ageing studies of the film showed long-term stability over 50 d. Carboxylic acid coatings have been deposited by PECVD onto cyclic olefin polymer substrates from an acrylic acid monomer. Carboxy properties are enhanced through the addition of TEOS as a base layer to the substrate, results are compared to coatings without this adhesion layer. A thorough analysis of the deposited surface and a comprehensive characterisation of the surface is investigated. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.