87 86 Principal Scientist Profiles Wolfgang Fritzsche Wolfgang Fritzsche Principal Scientist Profiles EXTERNAL LECTURER Apl. Prof. Dr. Wolfgang Fritzsche is head of the Department Nanobiophotonics at the Leibniz-Institute of Photonic Technology (Leibniz-IPHT). WOLFGANG FRITZSCHE RESEARCH AREAS The Nanobiophotonics group develops innovative methods for molecular detection based on the optical properties of plasmonic nanoparticles in combination with molecular components. This so-called Molecular Plasmonics includes passive approaches, such as the development of optical markers, and is focused on application of plasmon nanostructures for bioanalytics. On the other hand, in active plasmonics, plasmonic effects are used to manipulate biomolecules or for catalysis. • Passive Molecular Plasmonics: LSPR (localized surface plasmon resonance)-based bioanalytics • Active Molecular Plasmonics: plasmonic (nano)manipulation TEACHING FIELDS Dr. Fritzsche is involved in teaching Physical Chemistry as well as Instrumental Analytics for pharmacists, Optical Sensors/Microfluidics in the master‘s degree programme Medical Photonics, and Nanobiophotonics in the master‘s degree programme Chemistry of Materials. RESEARCH METHODS • Colloidal metal-nanoparticles, hybrid plasmonic nanostructures and plasmonic microarrays • Molecular techniques: self-assembly monolayers, biofunctionalization and conjugation of nanoparticles and nanostructures • (Imaging) spectroscopy of single plasmonic nanostructures and microarrays • Scanning Force Microscopy • Micro/nanointegration • Nanobiomanipulation (laser-irradiation of plasmonic antennas for manipulation of biomolecules) and plasmonic catalysis • DNA and protein detection using LSPR sensorics RECENT RESEARCH RESULTS The group’s research is focused on molecular plasmonics, as the interaction between molecular structures and metal nanostructures, and nanooptics. The main applications are in bioanalytics, where metal nanoparticles provide a label-free and quite sensitive detection using its property of localized surface plasmon resonance (LSPR). Besides composition, size and shape of the nanoparticle, the LSPR is also influenced by the refractive index of the surrounding matrix. Therefore, measurements of the shift of the LSPR wavelength allow for monitoring processes like biomolecular binding events at the level of individual gold nanoparticles. Nanoparticles of various materials, sizes and shapes are synthesized as well as characterized regarding structural and optical/spectroscopic properties, also at the single particle level. A variety of surface modification techniques including surface silanization have been established in order to bind these particles onto certain surfaces (chip substrates, but e.g. also inside hollow glass fibers), and to attach biomolecules, such as DNA or proteins. DNA nanotechnology is utilized to generate larger (>100 nm) superstructures (DNA origami) in order to allow for a more defined relative positioning of plasmonic particles and fluorophores. On the technical side, developments for a multiplexed readout of plasmonic properties of nanoparticles, to be realized by an imaging spectrometer based on a Michelson interferometer principle, are under way. Besides analytics, the interaction of laser light with particles is investigated regarding a manipulation of molecules (DNA) on a sub-molecular level, like DNA-restriction. An interesting effect was thereby discovered, which is based on electrons leaving the nanoparticle when excited by fs-laser pulses, and the transfer of this excitation along DNA nanowires over several micrometers. It clearly exceeds the generally accepted electron conductance of DNA of a few (maybe tens) of the nanometers, and is still the focus of ongoing investigation. FINETUNING PLASMONIC RESONANCES The localized surface plasmon resonance (LSPR,) as the resonant oscillation of conduction electrons in metal nanostructures upon light irradiation, is widely used for sensing as well as nanoscale manipulation. The spectral resonance band position can be mainly controlled by nanoparticle composition, size, and geometry and is slightly influenced by the local refractive index of the near-field environment. Here we introduce another approach for tuning, based on interference modulation of the light scattered by the nanostructure. Thereby, the incoming electric field is wavelength-dependently modulated in strength and direction by interference due to a subwavelength spacer layer between nanoparticle and a gold film. Hence, the wavelength of the scattering maximum is tuned with respect to the original nanoparticle’s LSPR. The scattering wavelength can be adjusted by a metallic mirror layer located 100 − 200 nm away from the nanoparticle, in contrast to nearfield gap mode techniques that work at distances up to about 50 nm in the nanoparticle environment. We have demonstrated, for the first time at the single nanoparticle level that depending on the interference spacer layer thickness, different distributions of the scattered signal can be observed, such as bell-shaped or doughnut-shaped point spread functions (PSF). The tuning effect by interference is furthermore applied to anisotropic particles (dimers), which exhibit more than one resonance peak, and to particles which are moved from air into the polymeric spacer layer to study the influence of the distance to the gold film in combination with a change of the surrounding refractive index. Plasmonic nanoparticles in spectral range UV-NIR, available from the Fritzsche Group. [1] Wirth et al., Nano Lett. 11, 1505 (2011). [2] Wirth et al., Nano Lett. 14, 570 (2014). [3] Wirth et al., Nano Lett., 14, 3809 (2014). Contact: Phone: + 49 3641 2-06304 Email: wolfgang.fritzsche@leibniz-ipht.de
RkJQdWJsaXNoZXIy OTI3Njg=