Fischer carbene mediated covalent grafting of a peptide nucleic acid on gold surfaces and IR optical detection of DNA hybridization with a transition metalcarbonyl label

Amine-reactive surfaces comprising N-hydroxysuccinimide ester groups as well as much more unusual Fischer alkoxymetallocarbene groups were generated on gold-coated surfaces via self-assembled monolayers of carboxy- and azido-terminated thiolates, respectively. These functions were further used to immobilize homothymine peptide nucleic acid (PNA) decamer in a covalent fashion involving the primary amine located at its N-terminus. These stepwise processes were monitored by polarization modulation reflection - absorption infrared spectroscopy (PM-RAIRS) that gave useful information on the molecular composition of the organic layers. PNA grafting and hybridization with complementary DNA strand were successfully transduced by quartz crystal microbalance (QCM) measurements. Unfortunately, attempts to transduce the hybridization optically by IR in a label-free fashion were inconclusive. Therefore we undertook to introduce an IR reporter group, namely a transition metalcarbonyl (TMC) entity at the 5\u2032 terminus of complementary DNA. Evidence for the formation of PNA-DNA heteroduplex was brought by the presence of \u3bd(C 61O) bands in the 2000 cm-1 region of the IR spectrum of the gold surface owing to the metalcarbonyl label

Gold/Polyoxometalate core/shell nanoparticles for combined chemotherapy/photothermal cancer therapy

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Nanostructured and spiky gold in biomolecule detection: improving binding efficiencies and enhancing optical signals

International audienceNanostructured gold can improve the ability to detect biomolecules. Whether planar nanostructured surfaces or nanostructured particles are used, similar principles governing the enhancement apply. The two main benefits of nanostructured gold are improved geometry and enhancement of optical detection methods. Nanostructuring improves the geometry by making surface-bound receptors more accessible and by increasing the surface area. Optical detection methods are enhanced due to the plasmonic properties of nanoscale gold, leading to localized surface plasmon resonance sensing (LSPR), surface-enhanced Raman scattering (SERS), enhancement of conventional surface plasmon resonance sensing (SPR), surface enhanced infrared absorption spectroscopy (SEIRAS) and metal-enhanced fluorescence (MEF). Anisotropic, particularly spiky, surfaces often feature a high density of nanostructures that show an especially large enhancement due to the presence of electromagnetic hot-spots and thus are of particular interest. In this review, we discuss these benefits and describe examples of nanostructured and spiky gold on planar surfaces and particles for applications in biomolecule detection

Time-of-flight secondary ion mass spectrometry investigation of the orientation of adsorbed antibodies on sams correlated to biorecognition tests

The adsorption of an antiglutamate dehydrogenase (Anti-GDH) antibody on different surfaces was studied to probe its orientation and bioactivity. Three different situations were investigated: physisorption on a -COOH-terminated thiols self-assembled monolayer (SAM) on gold, covalent grafting on the same SAM using NHS-EDC activation, and physisorption on a -CH3 SAM. The orientation of the antibody was investigated combining time-of-flight secondary ion mass spectrometry and principal component analysis. Several orientations are proposed for each case and compared to the results of biorecognition measurements with the antigen (GDH). At each step, protein layers were characterized ex-situ with polarization-modulated infrared reflection absorption spectroscopy and in situ (i.e., in the liquid phase) with quartz crystal microbalance with dissipation monitoring. Biorecognition measurements showed interesting correlations with proposed protein orientations. The role of hydrophobic and/or electrostatic interactions and that of covalent bonding are discussed to underline the influence of the orientation on the bioactivity of adsorbed Anti-GDH. © 2014 American Chemical Society

Probing the orientation of β-lactoglobulin on gold surfaces modified by alkyl thiol self-assembled monolayers

The adsorption of a globular protein on chemically well controlled surfaces was investigated in order to correlate its orientation to the surface properties. To this end, three different alkyl thiols, differing by their end group (-COOH, -CH3, and -NH2), were used to build up self-assembled monolayers (SAMs) on gold substrates. β-Lactoglobulin (βLG) was then adsorbed on these SAMs by immersion in a phosphate buffer solution. The surface modification with alkyl thiols and the subsequent adsorption of proteins were characterized ex situ by polarization modulated infrared reflection-absorption spectroscopy (PM-IRRAS) and X-ray photoelectron spectroscopy (XPS). The adsorption behavior of proteins was also monitored in situ using quartz crystal microbalance with dissipation measurements (QCM-D). Direct evidence regarding the protein orientation in the adsorbed state was obtained by means of time-of-flight secondary ion mass spectrometry (ToF-SIMS). Principal component analysis (PCA), performed on the ToF-SIMS results, enables to separate the samples and shows that the proteins display different distributions of amino acids at the surface depending on the conditioning thiol layer. Our results revealed that the adsorption mode of the protein is influenced by the thiol end groups, and specific orientations of the protein on the surface are proposed for the different substrates. © 2013 American Chemical Society

Synthesis and Antibacterial Properties of a New Generation of Hybrid Polyoxometalate / Antibiotic / Gold/Nanoparticle Nanocomposites

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Functionalisation of gold surfaces with thiolate SAMs: Topography/bioactivity relationship – A combined FT-RAIRS, AFM and QCM investigation

Immobilisation of rabbit immunoglobulin G (rIgG) was performed by affinity binding to protein A (PrA) covalently bound to threedifferent thiolate self-assembled monolayers (SAMs), (i) a mixed SAM of mercaptoundecanoic acid (MUA) and mercaptohexanol(C6OH) at a molar ratio of 1–3, (ii) a pure SAM of MUA and (iii) a pure SAM of cystamine (CA). A comparative study of anti-rIgGrecognition process on these three surfaces was achieved in order to assess the influence of the attachment layer topography and compositionupon the sensor quality. Functionalised gold-coated surfaces were characterised by three complementary analytical techniques,namely atomic force microscopy (AFM), polarization modulation–reflection-adsorption infrared spectroscopy (PM-RAIRS) and quartzcrystal microbalance (QCM). PM-RAIRS and AFM revealed that the three SAMs were formed on the gold surfaces. AFM observationsmade it clear that the thiolate and PrA layers were rather homogeneous in the case of pure MUA and CA SAMs, as compared to theMUA/C6OH mixed SAM on which PrA aggregates were observed. Though the highest amount of antibody was bound to the PrA onCA layer, higher anti-rIgG over IgG ratios were measured on the less dense layers of antibody

Synthesis and Characterization of Polyoxometalates/Antibiotics/Gold Nanoparticles Hybrid Materials for Antibacterial Applications

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