Development of a novel neural probe: Steps toward simultaneous measurement and differentiation of catecholamines in their mixtures.
by Lotfi Marchoubeh, Mahsa; Abrego Tello, Miguel; Pellegrino, Richard; Hu, Mengjia; Fritsch, Ingrid
Catecholamines (CAs) (dopamine (DA), norepinephrine (NE), and epinephrine (EP)) are important neurotransmitters and due to their role in neurol. diseases they have been of great scientific interest. Quantification of individual CAs in their mixts. has been a major challenge for existing electrochem. techniques. By using redox cycling, however, CAs can be differentiated and quantified based on their chem. reactions and diffusion within arrays of oxidative (generator) and reductive (collector) microelectrodes. Distinct rate consts. for intramol. cyclizations (step C) at pH= 7.4 in phosphate buffer allows for differentiation of CAs considering their ECC' mechanism. Signal amplification at the generator is based on the no. of times the species can shuttle within the array, leading to their quantification and detn. of detection limits whereas the signal at the collector can lead to differentiation. The probes designed for this research meet requirements of a redox cycling approach for in vivo measurements. These are: 1) mech. robustness for insertion in the brain without breakage or bending, 2) suitable dimensions to minimize damage to brain tissue and 3) suitable no. and design of electrodes for optimal electrochem. performance. The SU-8 substrate of the fabricated probe is an 80 µm thick. The shank is 100 µm wide and 6 mm long to reach deep areas of the rat's striatum. The probe has an array of nine parallel gold electrodes each of which are 4µm wide with a gap of 4 µm in between. We will report the process, results, and challenges for design, fabrication, and implementation of the probe. The characterization of the probe with a model compd. and the results from CA measurements using redox cycling will be shown. We will discuss the next steps to improve the design of electrodes and expts. to achieve desirable limits of detection and sensitivity for in vivo measurements.