title: Multi-photon excited luminescence of magnetic FePt core-shell nanoparticles.
abstract: We present magnetic FePt nanoparticles with a hydrophilic, inert, and biocompatible silico-tungsten oxide shell. The particles can be functionalized, optically detected, and optically manipulated. To show the functionalization the fluorescent dye NOPS was bound to the FePt core-shell nanoparticles with propyl-triethoxy-silane linkers and fluorescence of the labeled particles were observed in ethanol (EtOH). In aqueous dispersion the NOPS fluorescence is quenched making them invisible using 1-photon excitation. However, we observe bright luminescence of labeled and even unlabeled magnetic core-shell nanoparticles with multi-photon excitation. Luminescence can be detected in the near ultraviolet and the full visible spectral range by near infrared multi-photon excitation. For optical manipulation, we were able to drag clusters of particles, and maybe also single particles, by a focused laser beam that acts as optical tweezers by inducing an electric dipole in the insulated metal nanoparticles. In a first application, we show that the luminescence of the core-shell nanoparticles is bright enough for in vivo multi-photon imaging in the mouse neocortex down to cortical layer 5.
authors: Physik Department E21, Technische Universität München, D-85748 Garching, Germany ; Forschungsneutronenquelle Heinz Maier-Leibnitz, Technische Universität München, D-85747 Garching, Germany ; These authors contributed equally ; Klaus.Seemann@frm2.tum.de.
authors: K M
authors: KM
authors: Seemann
authors: Optical Neuroimaging Unit, Okinawa Institute of Science and Technology Graduate University, Onna-son, Okinawa 904-0495, Japan ; These authors contributed equally.
authors: B
authors: B
authors: Kuhn
keywords: (020.4180) Multiphoton processes; (160.4236) Nanomaterials; (170.2520) Fluorescence microscopy; (170.3880) Medical and biological imaging; (170.6280) Spectroscopy, fluorescence and luminescence; (300.6410) Spectroscopy, multiphoton