title: Charge binding of rhodamine derivative to OH- stabilized nanomaghemite: universal nanocarrier for construction of magnetofluorescent biosensors.
abstract: Superparamagnetic nanoparticles (20-40 nm) of maghemite, γ-Fe(2)O(3), with well-defined stoichiometric structure, are synthesized by the borohydride reduction of ferric chloride at an elevated temperature (100°C) followed by thermal treatment of the reaction product. Prepared maghemite nanoparticles reveal excellent colloidal stability for a long time without the necessity for any additional surface modification. These colloidal features are due to surface stabilizing OH(-) groups, which act as charge barriers preventing a particle aggregation and enabling a reversible binding of various oppositely charged organic substances. Such binding with rhodamine B isothiocyanate results in the fluorescent magnetic nanocarrier providing, at the same time, a spacer arm for covalent immobilization of other biosubstances including enzymes. In this work, we exploit this general applicability of the developed nanocarrier for covalent immobilization of glucose oxidase. This is the first reported example of magnetically drivable fluorescent nanocatalyst. The immobilized enzyme creates a 3-5 nm thick layer on the nanoparticle surface as proved by high-resolution transmission electron microscopy. This layer corresponds to 10 enzyme molecules, which are bound to the nanoparticle surface as found by the fluorimetric determination of flavin adenine dinucleotide. The developed magnetic fluorescent nanocatalyst, showing a rate constant of 32.7s(-1) toward glucose oxidation, can be used as a biosensor in various biochemical, biotechnological, and food chemistry applications. The presence of the nanocatalyst can be simply monitored by its fluorescence; moreover, it can be easily separated from the solution by an external magnetic field and repeatedly used without a loss of catalytic efficiency.
authors.affiliation: Department of Biological Chemistry, University of Padua, Padua, Italy.
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Magro
authors.forename: Giulietta
authors.initials: G
authors.lastname: Sinigaglia
authors.forename: Luca
authors.initials: L
authors.lastname: Nodari
authors.forename: Jiri
authors.initials: J
authors.lastname: Tucek
authors.forename: Katerina
authors.initials: K
authors.lastname: Polakova
authors.forename: Zdenek
authors.initials: Z
authors.lastname: Marusak
authors.forename: Sara
authors.initials: S
authors.lastname: Cardillo
authors.forename: Gabriella
authors.initials: G
authors.lastname: Salviulo
authors.forename: Umberto
authors.initials: U
authors.lastname: Russo
authors.forename: Roberto
authors.initials: R
authors.lastname: Stevanato
authors.forename: Radek
authors.initials: R
authors.lastname: Zboril
authors.forename: Fabio
authors.initials: F
authors.lastname: Vianello
mesh_terms: D015374:Biosensing Techniques; D005453:Fluorescence; D017665:Hydroxyl Radical / Q000737:chemistry*; D008280:Magnetics; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D012235:Rhodamines / Q000737:chemistry*; D015204:Spectroscopy, Mossbauer
chemical_list: D012235:Rhodamines; D017665:Hydroxyl Radical