Multi-layered plasma-polymerized chips for SPR-based detection.

The surface functionalization of a noble metal is crucial in a surface plasmon resonance-based biomolecular detection system because the interfacial coating must retain the activity of immobilized biomolecules while enhancing the optimal loading. We present here a one-step, room-temperature, high-speed, gas-phase plasma polymerization process for functionalizing gold substrates using siloxane as an adhesion layer and acrylic acid as a functional layer. Siloxane- and thiol-based coatings were compared for their performance as adhesion and the interfacial layer for subsequent functionalization. An in situ sequential deposition of siloxane and acrylic acid resulted in a 7-fold increase in carboxylic functionality surfacial content compared to films deposited with thiol-containing precursors. Grading of the layer composition achieved as a consequence of ion-induced mixing on the surface coating under the application of the plasma is confirmed through secondary ion mass spectroscopic studies. DNA hybridization assays were demonstrated on gold/glass substrates using surface plasmon enhanced ellipsometry and the applicability of this coating for protein immunoassays were demonstrated with plasma functionalized gold/plastic substrates in Biacore 3000 SPR instrument.

Plasma functionalization of AFM tips for measurement of chemical interactions.

In this paper, a new, fast, reproducible technique for atomic force microscopy (AFM) tips functionalization used for chemical interaction measurements is described. Precisely, the deposition of an aminated precursor is performed through plasma-enhanced chemical vapor deposition (PECVD) in order to create amine functional groups on the AFM tip and cantilever. The advantages of the precursor, aminopropyltriethoxysilane (APTES), were recently demonstrated for amine layer formation through PECVD deposition on polymeric surfaces. We extended this procedure to functionalize AFM probes. Titration force spectroscopy highlights the successful functionalization of AFM tips as well as their stability and use under different environmental conditions.

Functionalization of cycloolefin polymer surfaces by plasma-enhanced chemical vapour deposition: comprehensive characterization and analysis of the contact surface and the bulk of aminosiloxane coatings.

The surface science of bioassay devices is of great importance in the development of modern diagnostic platforms. The quality of surface is one of the most important elements of the device, often governing the background response, hence controlling the sensitivity of an assay. Detailed surface characterization and analysis are imperative for the preparation of reproducible coatings with desired properties. We performed a comprehensive characterization of 3-aminopropyl-triethoxysilane films prepared under two different deposition conditions on COP slides. Two sets of slides were prepared, by exposing them to plasma reaction for 30 seconds (A30 slide) and 4 minutes (A4 slide). While the variations in the deposition conditions seemed very subtle, the use of several powerful analytical tools helped us to reveal some fundamental differences between the studied films in terms of binding capacity, swelling and adhesion. Overall, the A30 films, with a thickness of 5.12 nm, showed up to 40% higher binding capacity and 25% better adhesion than the thicker A4 coatings (28.15 nm). Upon contact with aqueous media, a significant change was observed in terms of surface roughness. The A30 slides outperformed A4 slides, resulting in smoother surface, which is an important parameter for biomolecule immobilisation. The use of the techniques described in this article is aimed to set new standards for the characterization and analysis of the substrate surface of the future diagnostic devices.

Surface immobilisation of antibody on cyclic olefin copolymer for sandwich immunoassay.

In this work, the surface functionalisation of the commercially available cyclic olefin copolymer (COC) materials, Zeonor and Zeonex, has been studied. The methodology employed involved oxidation in oxygen plasma, functionalisation of the oxidized surface with aminopropyl triethoxy silane and, finally, attachment of antibody using covalent linker molecules. 1,4-Phenylene diisothiocyanate was selected as the most suitable cross-linker for the attachment of protein, as assessed by fluorescent intensity measurements on immobilised FITC-labelled IgG antibody. The modification method was characterised by contact angle measurements, ellipsometry, X-ray photoelectron spectroscopy (XPS) and fluorescence microscopy. The data are consistent with the deposition of a polymeric film of the silane chemisorbed to the oxidised plastic surface. The functionalised surfaces were employed in a sandwich immunoassay format using the reagents goat anti-human IgG (G alphaHIgG) and fluorescently labelled G alphaHIgG (Cy5-G alphaHIgG) as capture and detection antibodies, respectively, and with human IgG (HIgG) as the model analyte. The lowest concentration of HIgG detected was 0.1 ng ml(-1), with a relative standard deviation of 15%. Non-specific binding effects were also assessed. The method and supporting data demonstrate that simple approaches to surface functionalisation can be adapted to plastic-based devices.

Adsorption properties of the penicillin derivative DTPA on gold substrates.

Despite the large number of articles and patents dealing with penicillin and other beta-lactam antibiotics, there have been no reports about the self-assembly of such substances as monolayers on gold surfaces. The main reason stems from the high reactivity of the beta-lactam ring, which hinders the development of molecules possessing this entity together with a metal-anchoring function. Herein, we present the synthesis of a novel molecule, 6-[(R,S)-5-(1,2-dithiolan-3-yl)pentanoyl-amino]-penicillanic acid, which combines the beta-lactam ring and a metal-anchoring group. Using spectroscopic tools, we demonstrate the chemisorption of this compound on gold as self-assembled monolayers without any alteration of the penicillin pharmacophore and document its reactivity towards a penicillin-binding protein, BlaR-CTD. Our work is a preliminary step towards the development of new biosensors and well-ordered protein arrays, both based on the high affinity of penicillin for penicillin-binding proteins.

Use of specific functionalised tips with STM: a new identification method of ester groups and their molecular structure in self-assembled overlayers.

The influence of chemical modification of scanning tunnelling microscopy tips on image contrast is studied. This technique is applied to the identification of an ester functional group, hardly visible otherwise. Self-assembled overlayers of wax esters [CH3-(CH2)14-CO-O-(CH2)15-CH3], adsorbed at the interface between highly oriented pyrolitic graphite and a solution of phenyloctane, are imaged. The gold tips used are chemically modified by 4-mercaptobenzoic acid and 4-mercaptotoluene. The stability of the ordered overlayers formed facilitates the reproducible set of images with submolecular resolution. This allows the identification of the layer regular structure and of other features within molecules, which can be unambiguously related to the fingerprints of the COO bond. Moreover, we are interested in finding evidence of molecular motions observed at domain boundaries.