Publications

Most recent:

Angular Trapping of Anisometric Nano-Objects in a Fluid

 

We demonstrate the ability to trap, levitate, and orient single anisometric nanoscale objects with high angular precision in a fluid. An electrostatic fluidic trap confines a spherical object at a spatial location defined by the minimum of the electrostatic system free energy. For an anisometric object and a potential well lacking angular symmetry, the system free energy can further strongly depend on the object’s orientation in the trap. Engineering the morphology of the trap thus enables precise spatial and angular confinement of a single levitating nano-object, and the process can be massively parallelized. Since the physics of the trap depends strongly on the surface charge of the object, the method is insensitive to the object’s dielectric function. Furthermore, levitation of the assembled objects renders them amenable to individual manipulation using externally applied optical, electrical, or hydrodynamic fields, raising prospects for reconfigurable chip-based nano-object assemblies.  

M. Celebrano, C. Rosman, C. Sönnichsen, M. Krishnan

Nano Letters, ASAP, (DOI: 10.1021/nl303099c)

A New Approach to Assess Gold Nanoparticle Uptake by Mammalian Cells: Combining Optical Dark-Field and Transmission Electron Microscopy

 

Toxicological effects of nanoparticles are associated with their internalization into cells. Hence, there is a strong need for techniques revealing the interaction between particles and cells as well as quantifying the uptake at the same time. For that reason, we use optical dark-field microscopy in conjunction with transmission electron microscopy to investigate the uptake of gold nanoparticles into epithelial cells with respect to shape, stabilizing agent, and surface charge. The number of internalized particles is strongly dependent on the stabilizing agent, but not on the particle shape. A test of metabolic activity shows no direct correlation with the number of internalized particles. Therefore, particle properties besides coating and shape are suspected to contribute to the observed toxicity.

C. Rosman, S. Pierrat, A. Henkel, M. Tarantola, D. Schneider, E. Sunnick, A. Janshoff, C. Sönnichsen

Small, Early View, (DOI: 10.1002/smll.201200853)

 

 

Highly sensitive plasmonic silver nanorods

We compare the single-particle plasmonic sensitivity of silver and gold nanorods with similar resonance wavelengths by monitoring the plasmon resonance shift upon changing the environment from water to 12,5% sucrose solution. We find that silver nanoparticles have 1.2 to 2 times higher sensitivity than gold, in good agreement with simulations based on the boundary-elements-method (BEM). To exclude the effect of particle volume on sensitivity, we test gold rods with increasing particle width at a given resonance wavelength. Using the Drude-model of optical properties of metal together with the quasi-static approximation (QSA) for localized surface plasmons, we show that the dominant contribution to higher sensitivity  of silver is the lower background polarizability of the d-band electrons and provide a simple formula for the sensitivity. We improve the reversibility of the silver nanorod sensors upon repeated cycles of environmental changes by blocking the high energy parts of the illumination light.

A. Jakab, C. Rosman, Y. Khalavka, J. Becker, A. Trüdler, U. Hohenester, C. Sönnichsen

ACS Nano, 5 (9), 6880-6885 ( DOI: 10.1021/nn200877b)