A combination of a conductive material, such as carbon, with a transparent material, such as quartz makes this possible. It allows the creation of an optoelectrical device with integrated functions that takes advantage of the properties of both components’ materials.
“Carbon is a good electron conductor, with a stable surface resistant to common chemicals. This makes it a very good electrode material – which means carbon can add a sensing function to the device”, says Ada-Ioana Bunea.
Quartz is used for actuation
One of the options for generating carbon is through the pyrolysis of certain polymers. This adds versatility to the fabrication process, because polymers can be patterned using e.g. photolithography, and the pattern will be preserved after pyrolysis. In addition, carbon is biocompatible, which makes it a suitable substrate for the attachment of biological samples (e.g. stem cells, bacteria, thylakoids). To allow processing using pyrolysis, a thermally-resistant material is needed, and this is where quartz comes into play. Quartz is transparent in UV-Vis, so it can be used for actuation: Light can pass through the quartz areas of the device, and reach light-responsive biological samples attached to the carbon, triggering specific responses.
“During my PhD project, I fabricated and tested carbon-on-quartz devices for two very different purposes: Developing a biomedical implant for the treatment of Parkinson’s disease, and fabricating a bioanode for biophotovoltaics,” says Ada-Ioana Bunea.
The biomedical implant is based on commercial, optical fibers.
“Through pyrolysis, the polyimide polymer buffer commonly found on optical fibers turns into carbon, and we obtain a simple device which we named an optical fiber electrode. In the future, the quartz core will be used to guide light and stimulate the release of dopamine from light-responsive neurons, when the concentration of the neurotransmitter in the patient’s brain becomes too low,” Ada-Ioana Bunea explains.
This is currently being investigated at DTU Nanotech in the Training4CRM project led by professor Jenny Emnéus.
Figure 2: Images of stem cells growing and differentiating into dopaminergic neurons on optical fiber electrodes: A: Live stem cells during growth, imaged using confocal microscopy; B: differentiated cells in scanning electron microscopy; C: differentiated cells in confocal laser microscopy – the blue color indicates cells with the ability to release dopamine.