Novel Near-Infrared-Emitting (Nano)Materials for Bioimaging
von Gabriele Selvaggio
Datum der mündl. Prüfung:2022-08-22
Betreuer:Prof. Dr. Sebastian Kruss
Gutachter:Prof. Dr. Sebastian Kruss
Gutachter:Prof. Dr. Dietmar Stalke
EnglischThe scientific interest around in vivo biomedical imaging has strongly increased in recent years due to its benefits compared to other diagnostic tools. Fluorophores that emit in the near-infrared region of the electromagnetic spectrum (700 nm < λ < 1700 nm, NIR) present optimal features for bioimaging due to the higher tissue penetration, better contrasts and lower phototoxicity. Unfortunately, compared to the more established visible fluorophores, the library of NIR emitters is scarce. For these reasons, the interest in designing novel NIR-emitting platforms is very high. This doctoral thesis is dedicated to near-infrared fluorescent materials and most importantly a fluorescent silicate: Egyptian Blue (CaCuSi4O10, EB). Thanks to its layered crystal structure, this phyllosilicate could be easily exfoliated into 2D nanomaterials (i.e. nanosheets, NS) of dimensions well below the micron range. Most importantly, these EB-NS retained the bright, long-lived NIR emission of the bulk counterparts down to particles of just few tenths of nm in size. Furthermore, this NIR fluorescence proved to be highly photostable, as it did not bleach and was not significantly affected by quenching molecules, pH or ionic environments. Next to the study of the photophysical properties of these novel 2D nanomaterials, in vivo fluorescence microscopy and remote detection were demonstrated for the first time. Furthermore, successful covalent surface functionalization by Si-H activation of hydrosilanes was performed. In this way, colloidal stability could be enhanced and targeted bioimaging of cancer cells could be demonstrated. Given the versatility of the chosen surface chemistry, the biocompatible nature of EB-NS as well as the multiple outstanding properties of this material, the work in this doctoral thesis robustly established a novel NIR fluorophore for biophotonics. Besides EB-NS, similar materials were investigated in this doctoral thesis, too. Han Blue (BaCuSi4O10, HB) and Han Purple (BaCuSi2O6, HP) display similarity to EB in terms of crystal structure and photophysical properties. NS of all three silicates were therefore successfully prepared. As previously reported for EB-NS, also HB-NS and HP-NS retained their NIR fluorescence and displayed superior brightness and photostability under continuous illumination compared to state-of-the-art fluorophores. Via fluorescence lifetime imaging and spectroscopy tools, proof-of-principle experiments in the direction of NS lifetime detection and engineering were carried out as well. Finally, the potential held by another group of NIR fluorophores, i.e. the hexameric (H) and octameric (O) forms of extended benzene-fused oligo-BODIPYs, was investigated. For the first time, the NIR fluorescence features of these BODIPY-derivatives were presented and studied. The bright and tunable fluorescence of H- and O-oligo-BODIPYs displayed high promises for both remote detection and microscopy fluorescence imaging. Furthermore, H-coated microbeads were successfully employed for colocalized imaging and microrheology of actin networks, whose filaments displayed limited degradation despite prolonged excitation of the embedded H-dye. In summary, this thesis provides insights into preparation, surface chemistry and photophysics of NIR fluorescent materials and shows their potential in (bio)photonics.
Keywords: near-infrared fluorophores; bioimaging; spectroscopy; 2D nanomaterials; egyptian blue; han blue; han purple; BODIPY