Initial nanorods have been successfully synthesized. These nanorods of cylindrical shape possessed a cobalt core and a multi-layered shell consisting of a first tin layer, which itself was covered by a layer of platinum and gold. The cobalt core possessed magnetic properties, but was sensitive to oxidation, which impacted the magnetic properties. The layer of platinum and gold served to protect the cobalt core from oxidation once the nanorods were exposed to air or suspended in an aqueous solution.
Advanced nanorods have been synthesized possessing a cobalt core, an intermediate tin shell and an outer shell of gold. These nanorods were plasmon active and showed a longitudinal plasmon resonance peak at about 800 nm, which fitted the wavelength of the excitation of the photoacoustic imaging technology.
The nanorods were synthesized in an organic solvent, which was not biocompatible. Thus, the nanorod surface was modified and the nanorods were transferred to aqueous media. This was achieved by using a specific polymer, which comprised hydrophobic and hydrophilic parts. This polymer was wrapped around the nanorods. By this, stable nanorod dispersions were achieved in water, in salt solutions and in cell culture media.
The specific polymer also comprised segments that were used to bind additional molecules to the nanorod surface. This was employed to bind fluorescent dyes to the nanorod surface, which enabled reference imaging by conventional fluorescence microscopy. Additionally, antibodies were bound to the nanorods’ surface to target specific cell types. Furthermore, the surface of the nanorods was bio-functionalized to allow for the binding of glucose in a competitive assay format.
The nanoparticular contrast agent was employed to test its toxic effects on cells in vitro. Here, the results showed no toxic effect on cells. Based on these findings, the in vivo nanotoxicity was assessed with living zebrafish animal models. Again, no toxic effects were observed. Thus, the contrast agent could be safely administered to living zebrafish animal models for imaging purposes.
Another key development in the project was the development of the measurement setup including optical and magnetic components and custom software for imaging purposes. Here, a microscopy and a tomography-based setup were developed. The optical imaging modalities comprised optical coherence tomography and photoacoustic imaging. Additionally, we developed a high-speed magneto-plasmonic imaging setup based on optical coherence tomography.
Zebrafish animal models were cultivated, and we developed fish lines with highly reduced pigmentation. Reference imaging was conducted by conventional fluorescence microscopy. Retinal blood vessels and beta cells in the endocrine pancreas were imaged. This also served to verify that the circulation time of nanoparticular contrast agent within the blood stream was long enough to allow for imaging.
Magneto-plasmonic imaging with all three imaging modalities (microscopy, tomography, high-speed) was tested in phantom samples and in zebrafish embryos. The measurement principle was working and allowed for background removal. The fish survived the imaging session well, which was revealed by checking the heartbeat of the fish after imaging.
The SWIMMOT project and the results achieved have been disseminated to the general public via the social media accounts of the consortium partners, via a dedicated SWIMMOT homepage and a LinekdIn account. Furthermore, we organized two open public workshops in Santiago de Compostela and in Vienna dealing with molecular imaging and the application of nanomaterials for biomedical purposes. Additionally, the project and its results were presented in scientific workshops, conferences and via peer-reviewed publications. We gave a total of 33 talks and presented 17 posters. Currently, 13 research papers were published while several more are still under preparation. All research articles were published open access. Four master students and six PhD students performed their research supported by SWIMMOT. Numerous postdoctoral fellows from all partner institutions were able to continue their research path with the help and in the frame of the SWIMMOT project. During the project, the SWIMMOT consortium already teamed up with a European company which is among the world leaders in fabricating photoacoustic imaging technology, and they are very interested to join forces for the next development steps.
