Research

As a key part of the Cells in Motion Interfaculty Centre (CiMIC), the research group represents a central bridging unit between the Departments of Physics, Chemistry, Pharmacy and Biomedicine. By exploring the fundamental aspects of the interaction between light and matter, the Strassert Lab is devoted to the synthesis, engineering, and processing of (photo)functional coordination compounds towards innovative (nano)materials and tailored instrumental methods supported by theory. These tools are implemented for the optical manipulation of structural features and dynamic processes in living systems and as dual probes for high-resolution multimodal imaging, acting simultaneously as contrast agents for electron microscopy and as phosphorescent markers for spatially and temporally resolved luminescence micro(spectro)scopy.

© AK Strassert

Regarding (supra)molecular bioimaging, the Strassert Lab has been devoted to the development of NIR-absorbing luminescent and photoacoustic labels bridging the gap between high-resolution luminescence-based visualization and deep tissue imaging. In this sense, fine-tuning of photofunctional coordination compounds with exchangeable cationic centres enabled the realization of photosensitizers, fluorescent or photoacoustic reporters able to label and to (photo)inactivate antibiotic resistant bacteria and neoplastic cells while monitoring inflammatory responses. Moreover, phosphorescent Pt(II) complexes are used to site-specifically decorate bio(macro)molecules and polymers while providing contrast for electron microscopy. The resulting orthogonal readouts arising from one single probe are used to track their uptake in living cells via luminescence micro(spectro)scopy, and their localization is refined employing high-resolution electron microscopies.

Besides the pursuit of new synthetic concepts towards functional coordination compounds, the photophysical investigation plays a fundamental role towards an in-depth understanding of luminescent excited state properties at (supra)molecular level. State-of-the-art spectrally and temporally resolved luminescence analysis techniques are combined with the high spatial and temporal resolution of confocal optical microscopy with multiphoton excitation capabilities (including luminescence lifetime imaging microscopy). We characterize discrete luminescent entities or ensembles thereof in fluid solutions, homogeneous matrices, solids and films. This includes monomeric molecules or aggregates thereof confined at inert interfaces, in solvents or glassy matrices, crystals, fibres, nano- or microparticles, bacteria, biofilms, organelles, cells and tissues. Specific samples are investigated at variable temperatures (down to 6 K) to suppress roto-vibrational relaxation and thermal equilibration of triplet sub-states to assess spin-orbit-coupling-mediated zero-field splitting and thermally activated delayed fluorescence processes.

[20] AIE-Active Difluoroboron Complexes with N,O-Bidentate Ligands: Rapid Construction by Copper-Catalyzed C−H Activation. G. Tan, I. Maisuls, F. Strieth-Kalthoff, X. Zhang, C. G. Daniliuc, C. A. Strassert, F. Glorius. Advanced Science 2021, 8, 2101814  [DOI: 10.1002/advs.202101814]
[19] Conjugated Pt(II) Complexes as Luminescence-Switch-On Reporters Addressing the Microenvironment of Bacterial Biofilms. I. Maisuls, J. Singh, I. P. Salto, S. T. Steiner, T. M. Kirse, S. Niemann, C. A. Strassert, A. Faust. Inorganic Chemistry 2021, 60, 11058 [DOI: 10.1021/acs.inorgchem.1c00860]
[18] Intermolecular Interactions and Self-Assembly in Pt(II) Complex−Nanoclay Hybrids as Luminescent Reporters for Spectrally Resolved PLIM. S. C. Gangadharappa, I. Maisuls, I. P. Salto, S. Niemann, V. Bachtin, F. C. Herrmann, C. A. Strassert. Journal of Physical Chemistry C 2021, 125, 5739 [DOI: 10.1021/acs.jpcc.0c09835]
[17] Tuning energy landscapes and metal–metal interactions in supramolecular polymers regulated by coordination geometry. N. Bäumer, K. K. Kartha, S. Buss, I. Maisuls, J. P. Palakkal, C. A. Strassert, G. Fernandez. Chemical Science 2021, 12, 5236 [DOI: 10.1039/D1SC00416F]
[16] Ligand-controlled and nanoconfinement-boosted luminescence employing Pt(II) and Pd(II) complexes: from color-tunable aggregation-enhanced dual emitters towards self-referenced oxygen reporters. I. Maisuls, C. Wang, M. E. Gutierrez Suburu, S. Wilde, C. G. Daniliuc, D. Brünink, N. L. Doltsinis, S. Ostendorp, G. Wilde, J. Kösters, U. Resch-Genger, C. A. Strassert. Chemical Science 2021, 12, 3270 [DOI: 10.1039/D0SC06126C]
[15] Compensation of Hybridization Defects in Phosphorescent Complexes with Pnictogen-Based Ligands - A Structural, Photophysical, and Theoretical Case-Study with Predictive Character. S. C. Gangadharappa, I. Maisuls, D. A. Schwab,J. Kösters, N. L. Doltsinis, C. A. Strassert. Journal of the American Chemical Society 2020, 142, 21353 [doi: 10.1021/jacs.0c09467]
[14] Synthesis of Small-Molecule Fluorescent Probes for the In Vitro Imaging of Calcium-Activated Potassium Channel KCa3.1. K. Brömmel, S. Maskri, I. Maisuls, C. P. Konken, M. Rieke, Z. Pethö, C. A. Strassert, O. Koch, A. Schwab, B. Wünsch. Angewandte Chemie International Edition 2020, 59, 8277 [doi: 10.1002/anie.202001201]
[13] On-Surface Reactive Planarization of Pt(II) Complexes. J. Ren, M. Cnudde, D. Brünink, S. Buss, C. G. Daniliuc, L. Liu, H. Fuchs, C. A. Strassert, H.-Y. Gao, N. L. Doltsinis. Angewandte Chemie International Edition 2019, 58, 15396 [doi: 10.1002/anie.201906247]
[12] A platinum-doped dendrimer as a phosphorescent label for bacteria in two-photon excitation microscopy. N. Molina-Cabeza, M. Cnudde, J. A. Guadix, J. M. Perez-Pomares, C. A. Strassert, Y. Vida-Pol, E. Perez-Inestrosa. E. ACS Omega 2019, 4, 13027 [DOI: 10.1021/acsomega.9b00639]
[11] Light-Responsive Size of Self-Assembled Spiropyran–Lysozyme Nanoparticles with Enzymatic Function. D. Moldenhauer, J. P. Fuenzalida Werner, C. A. Strassert, F. Gröhn. Biomacromolecules 2019, 20, 979 [DOI: 10.1021/acs.biomac.8b01605]
[10] “Phosphorescent Pt(II) complexes spatially arrayed in micellar polymeric nanoparticles providing dual readout for multimodal imaging”, M. T. Proetto, J. Sanning, M. Peterlechner, M. Thunemann, L. Stegemann, S. Sadegh, A. Devor, N. C. Gianneschi, C. A. Strassert, Chem. Commun. 2019, 55, 501. [doi: 10.1039/c8cc06347h]
[9] “Towards Optimized Naphthalocyanines as Sonochromes for Photoacoustic Imaging in vivo”, M. J. Duffy, O. Planas Marques, A. Faust, T. Vogl, S. Hermann, M. Schäfers, S. Nonell Marrugat, C. A. Strassert, Photoacoustics 2018, 9, 49. [doi: 10.1016/j.pacs.2017.12.001]
[8] “Toward Tunable Electroluminescent Devices by Correlating Function and Submolecular Structure in 3D Crystals, 2D-Confined Monolayers, and Dimers”, S. Wilde, D. Ma, T. Koch, A. Bakker, D. Gonzalez-Abradelo, L. Stegemann, C. G. Daniliuc, H. Fuchs, H. Gao, N. L. Doltsinis, L. Duan, C. A. Strassert, ACS Appl. Mater. Interfaces 2018, 10, 22460. [doi: 10.1021/acsami.8b03528]
[7] “Oxygen-Insensitive Aggregates of Pt(II) Complexes as Phosphorescent Labels of Proteins with Luminescence Lifetime-Based Readouts”, P. Delcanale, A. Galstyan, C. G. Daniliuc, H. E. Grecco, S. Abbruzzetti, A. Faust, C. Viappiani, C. A. Strassert, ACS Appl. Mater. Interfaces 2018, 10, 24361. [doi: 10.1021/acsami.8b02709]
[6] “Oxygen-insensitive phosphorescence in water from a Pt-doped supramolecular array”, L. Straub, D. González-Abradelo, C. A. Strassert, Chem. Commun. 2017, 53, 11806. [doi: 10.1039/c7cc05435a]
[5] “Color-tunable asymmetric cyclometalated Pt(II) complexes and STM-assisted stability assessment of ancillary ligands for OLED”, J. Sanning, L. Stegemann, P. R. Ewen, C. Schwermann, C. G. Daniliuc, D. Zhang, N. Lin, L. Duan, D. Wegner, N. L. Doltsinis, C. A. Strassert, J. Mater. Chem. C 2016, 4, 2560. [doi: 10.1039/C6TC00093B]
[4] “Spatiotemporally Resolved Tracking of Bacterial Responses to ROS-Mediated Damage at the Single-Cell Level with Quantitative Functional Microscopy”, A. Barroso Peña, M. C. Grüner, T. Forbes, C. Denz, C. A. Strassert, ACS Appl. Mater. Interfaces 2016, 8, 15046. [doi: 10.1021/acsami.6b02605]
[3] “Labeling and Selective Inactivation of Gram-Positive Bacteria Employing Bimodal Photoprobes with Dual Readouts”, A. Galstyan, D. Block, S. Niemann, M. C. Grüner, S. Abbruzzetti, M. Oneto, C. G. Daniliuc, S. Hermann, C. Viappiani, M. Schäfers, B. Löffler, C. A. Strassert, A. Faust, Chem. Eur. J. 2016, 22, 5243. [doi: 10.1002/chem.201504935]
[2] “Photofunctional surfaces for quantitative fluorescence microscopy: Monitoring the effects of photogenerated reactive oxygen species at single cell level with spatiotemporal resolution”, L. Stegemann, K. C. Schürmann, C. A. Strassert, H. E. Grecco, ACS Appl Mater Interfaces 2015, 7, 5944. [doi: 10.1021/acsami.5b00130]
[1] “Scanning-tunneling-spectroscopy-directed design of tailored deep-blue emitters”, J. Sanning, P. R. Ewen, L. Stegemann, J. Schmidt, C. G. Daniliuc, T. Koch, N. L. Doltsinis, D. Wegner, C. A. Strassert, Angew. Chem. Int. Ed. 2015, 54, 786. [doi: 10.1002/anie.201407439]