128 research outputs found
Compound droplet manipulations on fiber arrays
Recent works demonstrated that fiber arrays may constitue the basis of an
open digital microfluidics. Various processes, such as droplet motion,
fragmentation, trapping, release, mixing and encapsulation, may be achieved on
fiber arrays. However, handling a large number of tiny droplets resulting from
the mixing of several liquid components is still a challenge for developing
microreactors, smart sensors or microemulsifying drugs. Here, we show that the
manipulation of tiny droplets onto fiber networks allows for creating compound
droplets with a high complexity level. Moreover, this cost-effective and
flexible method may also be implemented with optical fibers in order to develop
fluorescence-based biosensor
Compound droplets on fibers
Droplets on fibers have been extensively studied in the recent years.
Although the equilibrium shapes of simple droplets on fibers are well
established, the situation becomes more complex for compound fluidic systems.
Through experimental and numerical investigations, we show herein that compound
droplets can be formed on fibers and that they adopt specific geometries. We
focus on the various contact lines formed at the meeting of the different
phases and we study their equilibrium state. It appears that, depending on the
surface tensions, the triple contact lines can remain separate or merge
together and form quadruple lines. The nature of the contact lines influences
the behavior of the compound droplets on fibers. Indeed, both experimental and
numerical results show that, during the detachment process, depending on
whether the contact lines are triple or quadruple, the characteristic length is
the inner droplet radius or the fiber radius
Homogeneous Resonant Energy Transfer within Clusters of Monodisperse Colloidal Quantum Dots
peer reviewedAs fluorescent nanocrystals, colloidal quantum dots (QDs) are increasingly used for biosensing thanks to their ability to perform Förster resonant energy transfer (FRET). Especially, all-QD-based donor-acceptor systems offer promising approaches for the design of FRET biosensors. But contrary to molecular fluorophores, QD emission properties are highly conditioned by the size distribution of QDs, so it is possible to observe energy transfers between QDs coming from the same monodisperse population, when packed into clusters. Here, we characterize such homogeneous resonant energy transfer (homo-FRET) processes occurring between CdTe QDs clustered within an organosilane polymer matrix and develop a mathematical model to account for their efficiencies. We evidence the critical role of the statistical donor-acceptor polarization of the QD population and provide tools to quantify it. Interestingly, as QD-QD homo-FRET proves to only depend on size dispersion and Stokes shift, the conclusions of our study can be extended to any kind of QDs and our model can be used to predict their own homo-FRET efficiency
Characterization of CuInTe2 thin films prepared by flash evaporation
peer reviewedThin films of CuInTe2 were grown by flash evaporation. The influence of the substrate temperature Ts during film deposition on the properties of the thin films was examined. CuInTe2 films were structurally characterized by the grazing incidence x-ray diffraction (GIXD) technique. Investigation by this technique demonstrates that the surface of thin films of CuInTe2 prepared by flash vaporation at Ts > 100 °C exhibits the chalcopyrite structure with additional binary compounds in the surface. However, in the volume the films exhibit the chalcopyrite structure only; no foreign phases were observed. X-ray reflectometry was utilized to evaluate the critical reflection angle bc of CuInTe2 (bCuInTe2 c 0.32°) which permitted us to calculate the density of the films to be 6 g cm−3. The evaporated films were p type and the films deposited at Ts = 100 °C had a resistivity in the range 0.3–2 cm. From optical measurements we have determined the optical energy gap Eg 0.94 eV and the effective reduced mass m*r 0.07me
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
Etude des propriétés électriques et électro-optiques de jonctions métal-semi-conducteurs
Synthesis and adsorption properties of a penicillin derivative molecule, 6-[(R,S)-5-(1,2-dithiolan-3-yl)pentanoyl-amino]-penicillanic acid, on gold substrates
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