Enikő Krisch, Léa Messager, Benjámin Gyarmati, Valérie Ravaine, and András Szilágyi
Nanogels loaded with fluorescent dextran as a model drug are synthesized by the oxidation induced cross-linking of water soluble redox responsive thiolated poly(amino acid) in miniemulsion without the introduction of any cross-linker molecule. Two types of high energy methods, namely, ultrasonication and high pressure homogenization (HPH), are compared. Dynamic light scattering and transmission electron microscopy measurements confirm that spherical nanogels in 100–150 nm diameter range are prepared successfully by HPH method. Size and surface charge of the nanogels can easily be controlled by environmental pH. The release of encapsulated drug is triggered by the degradation of nanogels in reducing environment due to the cleavage of disulphide bonds.
Thibaut Divoux, Véronique Lapeyre, Valérie Ravaine, and Sébastien Manneville
Flows of suspensions are often affected by wall slip, that is, the fluid velocity Vf in the vicinity of a boundary differs from the wall velocity Vw due to the presence of a lubrication layer. While the slip velocity Vs = abs (Vf - Vw) robustly scales linearly with the stress S at the wall in dilute suspensions, there is no consensus regarding denser suspensions that are sheared in the bulk, for which slip velocities have been reported to scale as a Vs = k.(S)p with exponents p inconsistently ranging between 0 and 2. Here we focus on a suspension of soft thermoresponsive particles and show that Vs actually scales as a power law of the viscous stress (S - Sc), where Sc denotes the yield stress of the bulk material. By tuning the temperature across the jamming transition, we further demonstrate that this scaling holds true over a large range of packing fractions Phi on both sides of the jamming point and that the exponent p increases continuously with Phi, from 1 in the case of dilute suspensions to 2 for jammed assemblies. These results allow us to successfully revisit inconsistent data from the literature and pave the way for a continuous description of wall slip above and below jamming.
Bipolar electrochemistry (BPE) is widely used to trigger electrochemical reactions on conducting objects without direct electrical wiring. In this study a novel methodology is reported, which for the first allows simultaneous deposition of two different organic films at each end of a glassy carbon substrate (1 x 1 cm2). The approach is based on the use of an organic bifunctional molecule, which may be oxidatively and reductively electrografted at he same time. The reduction process goes through the diazonium group, while the oxidation proceeds via the primary amine. The double functinoalized plates are investigated by ellipsometry, cyclic voltammetry, condensation imaging, x-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry. Post-modification of one of the anchoring layers illustrates the versatility of the system, pointing to its potential use in fields going from molecular electronics to targeted drug delivery.
Florent Pinaud, Romain Millereux, Pierre Vialar-Trarieux, Bogdan Catargi, Sandra Pinet, Isabelle Gosse, Neso Sojic, Valérie Ravaine
Stimuli-responsive microgels with redox and luminescent resonance energy transfer (LRET) properties are reported. Poly(N-isopropylacrylamide) microgels are functionalized simultaneously with two models dyes: a derivative of tris(bipyridine) ruthenium complex and cyanine 5. Both moieties are chosen as a pair of luminophores with a spectral overlap for resonance energy transfer, where the ruthenium complex acts as a donor and the cyanine an acceptor. The effect of the temperature on the efficiency of the LRET of the microgels has been investigated and compared using either photoluminescence (PL) or electrochemiluminescence (ECL) as the excitation process. In PL, the synthesized microgels exhibit resonance energy transfer regardless of the swelling degree of the microgels. The transfer efficiency is a function of the donor–acceptor distance and can be tuned either by the swell–collapse phase transition or by the dye content in the microgel network. In ECL, the microgels emit light only at the wavelength of the ruthenium complex because the resonance energy transfer does not occur. Indeed, even within the microgel matrix, the cyanine dye is oxidized at the potential required for ECL generation, which impairs its emitting properties. Thus, both excitation channels (i.e., PL and ECL) show differential behavior for the resonance energy transfer processes.
V. Badets, D. Duclos, D. Quinton, O. Fontaine, D. Zigah
A dual gold-copper microelectrode (diameter 25 μm) was fabricated to be employed in a scanning electrochemical microscopy (SECM) configuration, and was used in feedback mode to both modify (write) and analyze (read) a substrate. This write-and-read procedure was performed on a glassy carbon electrode on which azide groups were introduced by electrochemical reduction of a diazonium salt. The copper part of the microelectrode was used to electrogenerate Cu(I) that catalyzed a “click” reaction between azide moieties on the surface and dissolved ethynylferrocene. This created a pattern of ferrocene moieties on the surface that was analyzed with the gold part of the microelectrode.
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