1 Department of Micro- and Nanotechnology, Technical University of Denmark2 Copenhagen Center for Health Technology, Center, Technical University of Denmark3 Center for Intelligent Drug Delivery and Sensing Using Microcontainers and Nanomechanics, Center, Technical University of Denmark
The monitoring of cellular behavior is useful for the advancement of biomedical diagnostics, drug development and the understanding of a cell as the main unit of the human body. Micro- and nanotechnology allow for the creation of functional devices that enhance the study of cellular dynamics by providing platforms that offer biocompatible surfaces for the cell culturing in lab-on-chip devices integrated with optimized nanosensors with high specificities and sensitivities towards cellular analytes. In this project, novel materials were investigated with a focus on providing suitable surface modifications for electrochemical nanosensors for the detection of analytes released from cells. Two type of materials were investigated, each pertaining to the two different aspects of such devices: peptide nanostructures were studied for the creation of cellular sensing substrates that mimic in vivo surfaces and that offer advantages of functionalization, and conducting polymers were used as electrochemical sensor surface modifications for increasing the sensitivity towards relevant analytes, with focus on the detection of dopamine released from cells via exocytosis. Vertical peptide nanowires were synthesized from diphenylalanine via a high temperature, aniline vapor assisted self-assembly process, yielding biological nanostructures 3-8 µm high and 200-300 nm in diameter grown from nanosensor surfaces and able to withstand cell culturing conditions. Several methods have been tested and optimized for the peptide nanowires' functionalization with biomolecules, metal nanoparticles and chemical functional groups such as thiols, showing the versatility and flexibility of this material's applications. A technique for the patterning of these nanostructures using soft lithography was also developed and tested for suitable cell sensing and culturing conditions. A study of the effect of these structures on the behavior of cell populations was carried out in vitro, utilizing PC12 cells as a differentiating stem cell neuronal model. The cells' growth, adhesion and morphology were characterized when cultured upon a surface of peptide nanowires. An in vivo investigation also gave evidence of how the peptide nanowires can be used as surface modification in implantable electrodes for neurological measurements. Conducting polymers were utilized in electrode modifications for electrochemical sensor surfaces. Both chemical and electrochemical deposition methods were used to optimize the polymer film with respect to sensitivity towards cellular analytes, each method chosen accordingly to specific electrode geometry and shape. Chemical polymerization of pyrrole was used to achieve conductive polymer film coatings for out-of-plane electrode structures without or with poor surface conductivity, providing a patternable conducting polymer deposition technique integrated with standard microfabrication techniques. Electropolymerization of pyrrole on planar interdigitated electrodes resulted in the creation of doped conducting polymer films. Different counter-ion dopants were tested, and the process was optimized in terms of electrochemical sensitivity towards dopamine. The doped polypyrrole modification was used for the in vitro detection of dopamine released via cellular exocytosis. Combinations of these materials were tested, and an integrated surface modification consisting of both peptide nanowires and conducting polymers was applied to an in vitro cell culturing and sensor platform for the detection of dopamine from PC12 cell populations, showing how the advantages of each material type can be united into a joint cellular nanosensor modification.