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

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

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

Naked Eye Immunosensing of Food Biotoxins Using Gold Nanoparticle-Antibody Bioconjugates

International audienc

Spiky gold shells on magnetic particles for DNA biosensors

International audienceCombined separation and detection of biomolecules has the potential to speed up and improve the sensitivity of disease detection, environmental testing, and biomolecular analysis. In this work, we synthesized magnetic particles coated with spiky nanostructured gold shells and used them to magnetically separate out and detect oligonucleotides using SERS. The distance dependence of the SERS signal was then harnessed to detect DNA hybridization using a Raman label bound to a hairpin probe. The distance of the Raman label from the surface increased upon complementary DNA hybridization, leading to a decrease in signal intensity. This work demonstrates the use of the particles for combined separation and detection of oligonucleotides without the use of an extrinsic tag or secondary hybridization step

Catalytic activity and thermostability of enzymes immobilized on silanized surface: Influence of the crosslinking agent

International audienceIn this work, we investigate the influence of crosslinkers on the operational and heat stability of immobilized enzymes on a silanized silicon surface. To this end, glucose-6-phosphate dehydrogenase (G6PDH), a model multimeric enzyme, was attached through bifunctional crosslinkers able to bind covalently the -NH2 in the silane layer and of amine residues in the enzyme. Five bifunctional crosslinkers in the form of "X-spacer-X" were used, differing by the reactive functional groups (X=aldehyde: -CHO, isothiocyanate: -NCS, isocyanate: -NCO), by the nature of the spacer chain (aromatic or aliphatic) or by the geometry (bifunctional groups positioned in meta- or para- on an aromatic ring). A thermostability enhancement has been obtained for enzymes immobilized using 1,4-phenylene diisothiocyanate (PDC) and 1,4-phenylene diisocyanate (DIC). Moreover, using the latter crosslinker, activity was the mostly preserved upon successive uses, thus giving the best operational stability achieved. Changing the geometry of the cross-linker, i.e., 1,4- as compared to 1,3-phenylene diisothiocyanate (PDC and MDC, respectively), has a crucial effect on operational and thermal stabilities. Indeed, among all used crosslinkers, the most important loss was observed for MDC (residual activity after 6 times use is ~16%). Using dialdehyde crosslinkers: glutaraldehyde (GA) and terephtalaldehyde (TE), activity was significantly less well preserved than with DIC and PDC (for GA and TE, a loss of about 50% at 30°C against no loss for PDC and DIC). These effects can be explained by a multipoint attachment model, in which a higher number of anchoring points stabilizes the three-dimensional structure and especially the binding of the two subunits in the active dimer, at the expense of a greater rigidity which is detrimental to the absolute activity. The differences observed with the crosslinkers are mainly due to steric hindrance at the interface which seems to be greatly influenced by the structure and the reactivity of the linkers