SFB 755 "Nanoscale Photonic Imaging" develops and applies high resolution optical methods to visualize structures and dynamics in space and time on the nanometer scale and on timescales extending over many orders of magnitude down to the femtosecond range.
The increase in resolution and the combination of nanoscale imaging with spectroscopic information is used to extend our capability to describe nanoscale biomolecular and complex fluid systems, under functionally relevant environmental parameters. Novel methods are developed to visualize macromolecular trajectories in aqueous solution and in living cells, to reconstruct the native density distribution in cells and tissues, or to trace inter-molecular interactions along with forces and chemical compositions well beyond the conventional resolution limits. The research areas covered include optical microscopy beyond the diffraction limit, multidimensional microscopy, spectroscopy with high spatial and temporal resolution, x-ray optics and x-ray imaging, lensless imaging, time dependent x-ray scattering, data reconstruction and inverse optical problems. During the second funding period, the intensive interaction of the experimental projects with mathematical projects has created a strong synergistic impact both on the development in optics and on mathematical methods. In addition, computer simulations of biomolecular dynamics are used to connect photon based experimental data to atomistic models.
Based on the successful development of the collaborative research centre, we now aim at even more challenging goals, some of which have already been formulated as long-term goals when the centre was established. Others have not been conceived as feasible but now seem within reach. A common motif in several projects is the increase in dimensionality of the imaging scheme. For example, high resolution methods, which have previously been two-dimensional, are now extended to three dimensions. At the same time, we are confident that a 3D x-ray tomography approach at the nanoscale can even be extended to time-resolved (4D) studies! In other instances, images are enhanced by increasing spectroscopic information. Along with the extended capabilities, quantification of the observables plays a major role. For example, where fluorescence brightness maps have been imaged at super-resolution, one may now go on and ask for the exact distribution and stoichiometry of molecules. The second funding period has provided several examples of enabling new tools. Reaching an unexpected 5 nm hard x-ray focus, optimizing the generation of short femto-second coherent EUV pulses, realizing unprecedented isotropic resolution in isoSTED visualizing living cells in x-ray darkfield and phase contrast, or realizing novel experiments at the Free Electron Laser sources have equally transformed our capabilities as the equivalent progress on the mathematical side, starting from the different solutions of the phase problem in imaging to advanced reconstruction and regularization approaches. Backed up by these results, we are now eager to further advance photonic imaging at the nanoscale!

The SFB755 is structured into three project groups:

A - Visible light beyond limits

The central goals of this section is the development of high-resolution visible-light based probe with applications aiming at unraveling

  • sub-cellular (oranelle) structures in live cells and tissues (A01),
  • the nanoscale dynamics, interaction and folding pathways of proteins (A05),
  • the glassy dynamics and relaxation of cross-linked biomoeluclar networkfs (A03),
  • metabolic transport processess by reconstruction of local molecular stoichiometries in the cell (A07).

To reach its central goal, the research program is significantly inter-connected. Common foci include:

  • reconstruction algorithms for nanoscopy data with residual inaccuracies (A01, A04, A06, A07),
  • correlative fluorescence and x-ray microscopy on test samples and cells (A01, A03, A06, B07, C01, C04)
  • stochastic multiscale analysis of Poisson count processes in photonic imaging (A04, A01, B04, C09)
  • tracking and simulation of conformational trajectories and folding pathways (A05), and
  • implemantation of novel optical force sensors based on DNA constructs and novel ultra stable optical probes based in single-walled carbon nanotubes (A03)

B - Spectromicroscopy of complex fluids

Just like during the first funding period, this area addresses the kinetics and self-assembly of (bio-)molecular systems over a broad range of time scales and at a high spatial resolution. An understanding of these phenomena requires the advanced methods described in sections A and C. In this funding period, central goals are a quantitative understanding of the

  • formation/structure of protein networks of stress fibers in cells and model systems (B07, B08),
  • kinetics of protein interaction, self-assembly and/or aggregation (B07, B08, A05),
  • structural transitions in photo-switchable proteins (B10, A01),
  • molecular structure and chemical reactions probed by short x-ray pulses (B03, B04, C10).

This project area takes ample advantage of the experimental methods already developed in sections A and C, which shall now be used with increased emphasis over the next funding period.In return, the experiments carried out in project area B will also help to validate the method developments made in A and C.

C - X-ray optics and imaging

The central goal of section C is the development of novel x-ray optical imaging tools, optimized x-ray optics, and phase retrieval algorithms which are then used also in B, and in A. Towards these goals, the synergistic research comprises:

  • uniqueness, i.e., identifiability, and numerical algorithms for the inverse scattering problem with reduced phase information, including holographic reconstructions (C01, C02),
  • image reconstruction (C01, C02, C11),
  • synchrotron and FEL experiments on hydrated cells (C10),
  • design, fabrication and implementation of advanced focusing optics (C01, C12),
  • wavefront measurement for FEL and HHG pulses and in-house CDI experiments with HHG radiation (C08),
  • x-ray microscopy using laser plasma sources (C04), and
  • inverse problems with Poisson data (C09).