|Abstract: ||Traumatic brain injury (TBI) is a major cause of death and disability worldwide. The focus of my research project is the study of potassium dynamics in spreading depolarisation (SD) waves found in TBI. The SD waves occur following the injury and the ionic imbalance caused by these waves causes further brain damage and greater patient morbidity. The goal of my research is to detect these waves in real time and quantify their severity in order to help clinicians better understand and treat TBI quickly and effectively to improve patient outcomes.
During my thesis project, I have first developed a miniaturised ion-selective electrode (ISE) for the detection of potassium (K+) transients associated with SDs. The average K+ ISE has a Nernstian sensitivity of 58.9 mV dec^−1 and temporal response of 5.1 seconds in the physiological range. The ISE, housed in a microfluidic flow cell with a sample volume of 70 nL, was applied in in vivo microdialysis studies to monitor real-time depolarisation waves. An SD wave causes the dialysate K+ to increase by 0.42 +/- 0.07 mM and 1.13 +/- 0.63 mM, from the physiological normal of 2.7 mM, in the animal model and in the human injured brains respectively. This dialysate SD marker has also been validated against tissue K+ level and cortical electrical activity which are currently the gold standards for SD detection.
In continuous or single-phase laminar flow, Taylor dispersion prevails. The result is an attenuated measured concentration to that captured at the microdialysis probe. With the development of a droplet microfluidic system, the dialysis stream can be segmented into discrete droplets suspended in a carrier oil, preserving the original concentration character-istics of the sample as well as improving the temporal resolution by ten-fold. The sample droplets can be manipulated passively to fulfil a range of operations, such as fast mixing, merging and splitting, and to enable parallelisation of analysis. Lastly, the droplets, now the core unit of analysis, are also reliably detected using a newly developed miniaturised contactless device based on conductivity, removing the need of expensive optical equipment and interference with the chemistry of the droplet.|