True Circular Dichroism in Optically Active Achiral Metasurfaces and Its Relation to Chiral Near-Fields

Optically active achiral metasurfaces offer a promising way to detect chiral molecules based on chiroptic methods. The combination of plasmonic enhanced circular dichroism and reversible optical activity would boost the sensitivity and provide enantiomerselective surfaces while using a single sensing site. In this work, we use metasurfaces containing arrays of U-shaped resonators as a benchmark for analyzing the optical activity of achiral materials. Although the peculiar optical activity of these metasurfaces has 1 been quite well described, we present here an experimental and numerical quantitative determination of the different contributions to the measured optical activity. In particular, it is shown that linear birefringence and retardance contribute, but only marginally, to the apparent circular dichroism of the metasurface associated with the excitation of magnetoelectric modes. We then numerically demonstrate the peculiar near-field properties of the magneto-electric modes and explain how these properties could be reflected in the far-field polarimetric properties in the presence of chiral molecules. This work provides alternatives for the detection scheme of chiral molecules using plasmonic resonators.Comment: ACS Applied Optical Materials, 202

All-quantum dot based Förster resonant energy transfer: key parameters for high-efficiency biosensing.

peer reviewedWhile colloidal quantum dots (QDs) are commonly used as fluorescent donors within biosensors based on Förster resonant energy transfer (FRET), they are hesitantly employed as acceptors. On the sole basis of Förster theory and the well-known behaviour of organic dyes, it is often argued that the QD absorption band over the UV-visible range is too wide. Discarding these preconceptions inherited from classical fluorophores, we experimentally examine the FRET process occurring between donor and acceptor CdTe QDs and provide a mathematical description of it. We evidence that the specific features of QDs unexpectedly lead to the enhancement of acceptors' emission (up to +400%), and are thus suitable for the design of highly efficient all-QD based FRET sensors. Our model enables us to identify the critical parameters maximizing the contrast between positive and negative biosensing readouts: the concentrations of donors and acceptors, their spectral overlap, the densities of their excitonic states, their dissipative coupling with the medium and the statistics of QD-QD chemical pairing emerge as subtle and determinant parameters. We relate them quantitatively to the measured QD-QD FRET efficiency and discuss how they must be optimized for biosensing applications

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

High efficiency amine functionalization of cycloolefin polymer surfaces for biodiagnostics

Point-of-care (POC) diagnostics implementing microfluidic technology on single use disposable plastic chips has potential applications in personalized medicine, clinical diagnostics and global health. However, the challenges in commercializing POC devices must be addressed. Immobilization of biomolecules to plastic chips through appropriate surface functionalization is a key issue for the fabrication of new generation biomedical diagnostic devices. The most important requirements for a practicable surface functionalization process are speed, control and reliability. Plasma-based methods can meet these criteria. A single step, solventless, ecofriendly and high throughput nature of plasma processing makes them highly attractive. Here we demonstrate the efficient surface functionalization of a next-generation biosensor material, a chemically inert cycloolefin polymer (COP). The plasma formation of a surface-bound aminated siloxane network from mixed aminopropyltriethoxysilane and ethylenediamine precursors allowed us to form a well-adherent film with an exceptionally high degree of amine functionalization. We deduce that the siloxane was the critical component for radical insertion into the COP and for building a stable network to support the reactive amine functionalities. We present a full physical and chemical characterization of the films, including a detailed study of their swelling in water, using an array of surface analytical techniques: X-ray photoelectron spectroscopy, X-ray reflectivity, reflection infra-red spectroscopy, atomic force microscopy (AFM) and fluorophore binding reactions. We demonstrate an original approach for qualitatively analyzing the distribution of amine functionalities by counting surface-bound functionalized silica nanoparticles in the AFM. The relative contributions from covalent (specific) and non-covalent (non-specific) reaction chemistry assessed using 3�-fluorescein-labeled ssDNA attachment showed that the non-specific binding could be reduced significantly according to the particular feed gas mixture used to prepare the coating. A reaction mechanism has been proposed for the deposition of amine functionalities on COP plastic and also for enhancing the amine functionalities that affect the non-specific binding significantly. © 2010 The Royal Society of Chemistry

Nanoparticules d’or pour les biocapteurs : lecture optique de la reconnaissance moléculaire

Les propriétés extraordinaires des nanoparticules d’or et/ou d’argent en ont fait des objets courtisés par les scientifiques toutes disciplines confondues. L’intensité de leur couleur ainsi que leur grande sensibilité optique au milieu environnant en font de puissants transducteurs pour les biocapteurs ; que ce soit grâce à des spectrophotomètres ou simplement par observation à l’oeil nu. Elles assurent la lecture de la reconnaissance moléculaire via des scénarios variés alliant simplicité et faible coût

Interaction des complexes aminés du nickel (II) et des halogénoplatinates (IV) avec la silice (vers une reconnaissance moléculaire aux interfaces)

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Gold Colloid-Nanostructured Surfaces for Enhanced Piezoelectric Immunosensing of Staphylococcal Enterotoxin A

International audienceWe describe the use of gold nanoparticles (AuNP) as a nanostructuring agent on quartz crystal sensor chips to engineer staphylococcal enterotoxin A (SEA) piezoelectric biosensors with amplified response. AuNPs were assembled on gold- or silicon-coated quartz crystal sensor chips by a wet chemistry process involving their chemisorption to preformed thiol and amine terminated Self-Assembled Monolayers (SAMs). The purpose of this nanostructuration was to modify the topography of the surface and improve the accessibility of the binding sites on the surface of the sensor chips. Biointerfaces, comprising a polyclonal antibody against staphylococcal enterotoxin A (SEA), were further built up on these gold nanoparticle-coated sensors and their ability to capture SEA was monitored in real time with a quartz crystal microbalance with dissipation monitoring. It was found out that, although the surface density in capture antibody was similar on both nanostructured and planar sensors, the sensor response, expressed as frequency shift recorded during the binding of SEA to the antibody, was significantly higher for the nanostructured sensors as compared to the planar ones. All the same, the limit of detection was lower for the nanostructured sensors: 8 ng/mL vs 20 ng/mL for the planar sensors. This was rationalized by a possibly better accessibility of the antigen binding sites rather than a consequence of specific surface increase. Using a sandwich type assay, gold nanoparticles coated silicon quartz sensor chips provided the lowest limit of detection of ca. 1 ng/mL in a total assay time of 25 min