Colloidal, monodisperse CdSe nanocrystals were homogeneously dispersed in an ionic liquid and investigated by means of cyclic voltammetry. Almost all known defect states in semiconductor nanocrystal were quantitatively measured with this nonoptical method (including nonradiative defect states). Variation of the illumination and temperature resulted in excitation of defect-trapped electrons into the conducting band. Thus, we succeeded for the first time to correlate defect states in nanocrystals with those in the corresponding bulk crystals.

Low toxic InP/ZnS quantum dots (QDs), ZnS:Mn(2+)/ZnS nanocrystals and CdSe/ZnS nanoparticles were rendered water-dispersible by different ligand-exchange methods. Eventually, they were coated with bovine serum albumin (BSA) as a model protein. All particles were characterised by isotachophoresis (ITP), laser Doppler velocimetry (LDV) and agarose gel electrophoresis. It was found that the electrophoretic mobility and colloidal stability of ZnS:Mn(2+)/ZnS and CdSe/ZnS nanoparticles, which bore short-chain surface ligands, was primarily governed by charges on the nanoparticles, whereas InP/ZnS nanocrystals were not charged per se. BSA-coated nanoparticles showed lower electrophoretic mobility, which was attributed to their larger size and smaller overall charge. However, these particles were colloidally stable. This stability was probably caused by steric stabilisation of the BSA coating.

[a] Colloidal group II B -VI semiconductor nanocrystals (so-called quantum dots or QDs) have attracted increasing interest among the research community because of their mesoscopic, size-dependent electro-optical properties. These properties make these novel materials highly desirable for potential applications, such as labeling of biomolecules, [1][2][3] catalysis, [4] phosphors, [5] light-emitting diodes (LEDs) [6][7][8][9][10][11][12][13] or photovoltaic cells. [14][15][16] Especially the latter applications require a fundamental knowledge of the charge-transfer kinetics of these particles. So far, it was not possible to measure these parameters in colloidal nanocrystals, because the appropriate electrochemical techniques require a supporting electrolyte to be added to the colloid, which causes such particles to precipitate. Therefore, only nanocrystal films (aggregates) and "water-soluble" colloidal nanocrystals were studied under this perspective. [17][18][19] Ionic liquids (ILs) have recently emerged as neoteric solvents for all kinds of chemical applications.[20] Among many other fields, they have been used for organometallic catalysis [21] and process engineering, as well as for electrochemical applications, [22] such as electrodeposition of semiconductors. [23] ILs are liquid materials that-similar to salts-consist completely of ions, but as opposed to commonly known "molten salts", which are high-melting and highly corrosive, ILs have a relatively low melting point (below 100 8C by a common definition; [24] many are liquid at room temperature and below), are often of relatively low viscosity and noncorrosive. Thus, they can be used as solvents for chemical applications.ILs are excellent electrolytes for electrochemical measurements because they are very flexible regarding their anions, cations and substituents (ILs are frequently called "designer solvents" [25] ). The realization of a nanocrystal colloid in ILs not only combines two intriguing fields, but also enables electrokinetic measurements of colloidal nanocrystals with hydrophobic ligands to be performed for the first time. Herein, we report the transfer of colloidal nanocrystals into an appropriate IL and the first electrokinetic measurements with these new colloids. We were not only able to observe the quantum-size effect (QSE) with differently sized nanocrystals, but also to estimate charge-transfer rates on ionization.For measuring the charge transfer of colloidal nanocrystals two requirements must be met: First, the electrolyte (namely, the IL) has not to evince oxidation and reduction processes in the region of the ionization potential and electron affinity of the nanocrystals. Secondly, the nanocrystals have to be colloidally stable within this IL. "As synthesized" nanocrystals are mostly sterically stabilized with nonpolar ligands. Therefore, we prepared different ILs with increased nonpolar character. The ILs are based on two cations: 1-methyl-3-alkyl-imidazolium (C x mim), which is by far the most widely used IL cation in the chemica...

Efforts were made to realise a two-dimensional, on-line-coupled isotachophoresis-capillary zone electrophoresis system. The electrophoretic behaviour of gold nanoparticles was investigated with the idea that they could be used to improve the control of this electrophoretic set-up. The well-known citrate-ligated gold nanoparticles were not suitable for this application, because the ligand was desorbed, and the nanoparticle solutions were degraded. Therefore mercaptocarboxylic acids were used, because the chemisorption of thiols on the gold surface was improved. Isotachophoretic measurements were carried out with these nanoparticles. A size-dependent electrophoretic mobility was found according to theoretical predictions, and the surface and zeta-potential were discussed for the small particle range. A new method for concentration measurements of nanoparticles is presented by means of isotachophoresis.