Ultra-high Q/V Fabry-Perot microcavity on SOI substrate

International audienceWe experimentally demonstrate an ultra high Q/V nanocavity on SOI substrate. The design is based on modal adaptation within the cavity and allows to measure a quality factor of 58.000 for a modal volume of 0.6(λ/n)3. This record Q/V value of 105 achieved for a structure standing on a physical substrate, rather than on membrane, is in very good agreement with theoretical predictions also shown. Based on these experimental results, we show that further refinements of the cavity design could lead to Q/V ratios close to 106

Photonics at nanometer scale: tracking light in high Q low V nanocavities

Photonic crystals (PCs) have proven to be an efficient way to tightly confine the electromagnetic field in nanocavities or slow down light propagation within optical waveguides. Very recently it has been proposed to use a nanometric optical probe to observe in near-field the light confinement and propagation within PC devices. In this work we analyze the optical properties of PC nanostructures by using a SNOM probe in collection mode in association with transmission measurements. We also explore the possibility to use the nanometric tip for a new class of Near-field Optics Nanometric Silicon Systems (NONSS) dedicated to on-chip information routing and processing. In a first step, we show that with to the SNOM probe it is possible to evidence different light behaviours depending on optical mode profile. Mode coupling in PC waveguides and quality factor changes in PC nanocavities will be discussed. Then in a second step, we show that strong field confinement enhancement can be achieved in nanocavities by proper mirror designs including mode matching and losses recycling. A quality factor (Q) enhancement by two orders of magnitude is observed. These experimental results are discussed in light of numerical calculations. Finally, in a third step, we fabricated a nanocavity in a monomode SOI ridge waveguide with an ultimately low microcavity modal volume of 0.6(l/n)^3. We use this high-Q low-V nanocavity to explore the nanocavity - nanometric optical probe interaction

E4F1-mediated control of pyruvate dehydrogenase activity is essential for skin homeostasis.

The multifunctional protein E4 transcription factor 1 (E4F1) is an essential regulator of epidermal stem cell (ESC) maintenance. Here, we found that E4F1 transcriptionally regulates a metabolic program involved in pyruvate metabolism that is required to maintain skin homeostasis. E4F1 deficiency in basal keratinocytes resulted in deregulated expression of dihydrolipoamide acetyltransferase (Dlat), a gene encoding the E2 subunit of the mitochondrial pyruvate dehydrogenase (PDH) complex. Accordingly, E4f1 knock-out (KO) keratinocytes exhibited impaired PDH activity and a redirection of the glycolytic flux toward lactate production. The metabolic reprogramming of E4f1 KO keratinocytes associated with remodeling of their microenvironment and alterations of the basement membrane, led to ESC mislocalization and exhaustion of the ESC pool. ShRNA-mediated depletion of Dlat in primary keratinocytes recapitulated defects observed upon E4f1 inactivation, including increased lactate secretion, enhanced activity of extracellular matrix remodeling enzymes, and impaired clonogenic potential. Altogether, our data reveal a central role for Dlat in the metabolic program regulated by E4F1 in basal keratinocytes and illustrate the importance of PDH activity in skin homeostasis

Improved functionalization of oleic acid-coated iron oxide nanoparticles for biomedical applications

Superparamagnetic iron oxide nanoparticles can providemultiple benefits for biomedical applications in aqueous environments such asmagnetic separation or magnetic resonance imaging. To increase the colloidal stability and allow subsequent reactions, the introduction of hydrophilic functional groups onto the particles’ surface is essential. During this process, the original coating is exchanged by preferably covalently bonded ligands such as trialkoxysilanes. The duration of the silane exchange reaction, which commonly takes more than 24 h, is an important drawback for this approach. In this paper, we present a novel method, which introduces ultrasonication as an energy source to dramatically accelerate this process, resulting in high-quality waterdispersible nanoparticles around 10 nmin size. To prove the generic character, different functional groups were introduced on the surface including polyethylene glycol chains, carboxylic acid, amine, and thiol groups. Their colloidal stability in various aqueous buffer solutions as well as human plasma and serum was investigated to allow implementation in biomedical and sensing applications.status: publishe