Luminescence of Amphiphilic PtII Complexes Controlled by Confinement.

The formation of hybrid silica-based systems to study the effect of the confinement on the emission properties of self-assembled platinum(II) complexes is reported. The complexes behave as surfactants since they possess a hydrophobic moiety and, on the ancillary ligand, a relatively long hydrophilic chain terminated with a positively charged group. The compounds, soluble in water, self-assemble, even at very low concentration, in supramolecular structures which display an orange luminescence. The properties of the assemblies have been studied in detail and in order to stabilize these supramolecular architectures and to enhance their emission properties hybrid silica porous nanoparticles have been prepared. In particular the PtII complexes have been employed as co-surfactant for the template formation of mesoporous silica nanoparticles (MSNs) using a sol gel synthesis. Interestingly, upon encapsulation in the silica pores, the platinum aggregates exhibit an emission profile similar in energy to the complexes assembled in solution, but the photoluminescence quantum yields of the hybrid systems are significantly higher (up to 45 %), and the excited state lifetimes much longer than those recorded in solution. Such enhancement of the photophysical properties together with the possibility to process the hybrid silica nanomaterials can pave the way to new type of emitters.

Glucose-Modified Silicon Nanoparticles for Cellular Imaging.

Luminescent silicon nanoparticles have recently attracted attention due to their remarkable stability, covalent functionalisation and tunable photoemission properties. Owing to their biocompatibility, low toxicity, and the small particle size that can be achieved by different synthetic approaches, these nanomaterials are candidates as cellular probes in the field of bioimaging, and potentially for in vivo applications. Tailoring the surface of the particles with active biomolecules such as sugar moieties can be an interesting strategy to increase the kinetics of internalisation or to vary the localisation of nanosystems in living cells. In this study, we synthesised and modified ultrasmall silicon nanoparticles with glucose covalently linked on their surface. Moreover, by varying the ratio between the amount of silicon nanoparticles and the saccharide groups, the amount of glucose, as a capping moiety, can be well controlled. FTIR spectroscopy, NMR spectroscopy, zeta potential measurements and anisotropy decay analysis confirmed the covalent binding of glucose to the nanoparticles. The photophysical behaviour of the surface-functionalised silicon quantum dots was not significantly different to that of the unmodified nanoparticles. In vitro studies demonstrated faster internalisation of the glucose-functionalised nanoparticles into HeLa cells. Different localisation and uptake kinetics of the glucose-modified particles compared to the unmodified particles are discussed in order to reveal the role played by the sugar molecules.

Modular Graphene-Based 3D Covalent Networks: Functional Architectures for Energy Applications.

The development of ordered graphene-based materials combining high stability, large surface areas, ability to act as absorbent of relevant chemical species, and solution processability is of significance for energy applications. A poorly explored approach relies on the controlled nanostructuration of graphene into robust and highly ordered 3D networks as a route to further leverage the exceptional properties of this unique material. Here, a simple yet effective and scalable one-step method is reported to prepare graphene-based 3D covalent networks (G3DCNs) with tunable interlayer distance via controlled polymerization of benzidines with graphene oxide at different reaction temperatures under catalyst- and template-free conditions. The reduced form of G3DCNs is used as electrodes in supercapacitors; it reveals a high specific capacitance of 156 F g(-1) at a current density of 1 A g(-1) in a two-electrode configuration and 460 F g(-1) at a current density of 0.5 A g(-1) in a three-electrode configuration, combined with an excellent cycling stability over 5000 cycles. The present study will promote the quantitative understanding of structure-property relationship, for the controlled fabrication of 3D graphene-based multifunctional materials.

Reactivity mapping with electrochemical gradients for monitoring reactivity at surfaces in space and time.

Studying and controlling reactions at surfaces is of great fundamental and applied interest in, among others, biology, electronics and catalysis. Because reaction kinetics is different at surfaces compared with solution, frequently, solution-characterization techniques cannot be used. Here we report solution gradients, prepared by electrochemical means, for controlling and monitoring reactivity at surfaces in space and time. As a proof of principle, electrochemically derived gradients of a reaction parameter (pH) and of a catalyst (Cu(I)) have been employed to make surface gradients on the micron scale and to study the kinetics of the (surface-confined) imine hydrolysis and the copper(I)-catalysed azide-alkyne 1,3-dipolar cycloaddition, respectively. For both systems, the kinetic data were spatially visualized in a two-dimensional reactivity map. In the case of the copper(I)-catalysed azide-alkyne 1,3-dipolar cycloaddition, the reaction order (2) was deduced from it.

Shape-controlled fabrication of micron-scale surface chemical gradients via electrochemically activated copper(i) "click" chemistry.

We report an electrochemical method for the shape-controlled fabrication of micron-scale surface-bound chemical gradients. The approach is based on employing platinum microelectrode arrays on glass for the establishment of a Cu(i) solution gradient via local electrochemical reduction of Cu(ii) (cathodic reaction), and oxidation of the generated Cu(i) back to Cu(ii) (anodic reaction), under ambient conditions. The Cu(i) solution gradient, in the presence of an alkyne in solution and an azide monolayer on the glass surface in between the platinum electrodes, is exploited for the surface-confined gradient fabrication via the Huisgen 1,3-dipolar cycloaddition (CuAAC). Owing to the high sensitivity of the CuAAC on the Cu(i) concentration, we demonstrate here the control of the shape of the micron-scale surface gradient, in terms of steepness and surface density, as a function of the reaction conditions. The surface gradients were assessed by fluorescence microscopy and time-of-flight secondary ion mass spectrometry (Tof-SIMS). Moreover, bi-component and biomolecular gradients have been fabricated and a method for the electrochemically mediated patterning of surface chemical gradients on external azide-functionalized substrates has been developed for the implementation of bi-directional 2D surface gradients.