Spherical magnetite nanoparticles (MNPs, 24 nm in diameter) were sequentially functionalized with trimethoxysilylpropyldiethylenetriamine (TMSPDT) and a synthetic DNA intercalator, namely, 9-chloro-4H-pyrido[4,3,2-kl]acridin-4-one (PyAcr), in order to promote DNA interaction. The designed synthetic pathway allowed control of the chemical grafting efficiency to access MNPs either partially or fully functionalized with the intercalator moiety. The newly prepared nanomaterials were characterized by a range of physicochemical techniques: FTIR, TEM, PXRD, and TGA. The data were consistent with a full surface coverage by immobilized silylpropyldiethylenetriamine (SPDT) molecules, which corresponds to 22300 SPDT molecules per MNP and a subsequent (4740 − 2940) PyAcr after the chemical grafting step (i.e., 2.4 PyAcr/nm2). A greater amount of PyAcr (30600) was immobilized by the alternative strategy of binding a fully prefunctionalized shell to the MNPs with up to 16.1 PyAcr/nm2. We found that the extent of PyAcr functionalization strongly affects the resulting properties and, particularly, the colloidal stability as well as the surface charge estimated by ζ-potential measurement. The intercalator grafting generates a negative charge contribution which counterbalances the positive charge of the single SPDT shell. The DNA binding capability was measured by titration assay and increases from 15 to 21.5 μg of DNA per mg of MNPs after PyAcr grafting (14−20% yield) but then drops to only 2 μg for the fully functionalized MNPs. This highlights that even if the size of the MNPs is obviously a determining factor to promote surface DNA interaction, it is not the only limiting parameter, as the mode of binding and the interfacial charge density are essential to improve loading capability.
We report two methods to prepare ordered macroporous ruthenium oxide electrodes based on a template approach and their possible applications as potentiometric and amperometric sensors. The very stable porous electrodes have been prepared using two techniques to assemble the colloidal template: the controlled evaporation (CE) technique and the Langmuir-Blodgett (LB) technique, followed by electrochemical deposition of ruthenium oxide. The increased surface area of the macroporous structure makes them attractive for electroanalytical applications such as potentiometric and amperometric sensors as is illustrated for pH sensing and direct oxidation of NADH, which is an ingredient in dehydrogenase based biosensors.
A bulk procedure based on bipolar electrochemistry is proposed for the generation of Janus-type carbon tubes. The concept is illustrated with carbon tubes, that are selectively modified at their ends with various metals and conducting polymers. No surface or interface is required to break the symmetry and therefore this approach could be used for the mass production of Janus micro- and nanoobjects. We show evidence that the technique is very versatile, allowing to choose the kind of material that is deposited and whether the end product is mono- or bifunctionalized.
Transport, reactivity and interactions of anti-tumor ferrocene-based compounds within lipid environments have been investigated electrochemically at a glassy carbon electrode (GCE) modified with a lipid bilayer film. Cyclic voltammetry performed in the presence of an adsorbed bilipid film in a H2O/EtOH (8/2) mixture, clearly showed that the affinity of the starting neutral ferrocifen derivatives towards the lipidic bilayer depends on both their size and their polarity. Likewise, the electrogenerated ferrocenium derivatives were expulsed reversibly from the bilayer in agreement with their positive charge. The reactivity of ferrocifen compounds was also investigated under the same conditions and in the presence of a base in order to trigger an intramolecular ferrocene-mediated (−2e −2H+) process within the lipidic film. Under these conditions, two distinct sequential electrochemical behaviors were observed depending on the base availability in the lipid layer, the magnitude of the corresponding two electrons wave being limited by the base concentration in the film. A full two-electron oxidation process, was observed as long as the amount of base present into the lipid layer was high enough to titrate the two protons released in the two-electron process. When this was sub-stoichiometric a second wave was observed at higher potential values representing the one electron oxidation of the ferrocifen excess.
A microdevice based on transparent indium tin oxide (ITO) electrodes allows simultaneous total internal reflection fluorescence microscopy and amperometric measurements. Use of the device in the coupled optical and electrochemical detection of single exocytotic events is demonstrated with enterochromaffin BON cells.