Developing an electrochemical tissue perfusion sensor

Abstract

This thesis focuses on the development of an electrochemical tissue perfusion sensor. Tissue perfusion is the cellular level mass transport mechanism which describes the movement of nutrients and metabolites within in tissue and is a measure of tissue health. Our understanding of tissue perfusion is still limited because current measurement tools are inadequate. The tissue perfusion measurement technique developed overcomes the limitation of current methods in that continuous and cellular level measurements are possible. This is achieved using a platinum ring-disc microelectrode operated in the collector-generator mode. This electrode pair is placed in tissue where one electrode generates hydrogen whilst the other collects it. Tissue perfusion will strongly influence the movement of H2 between the two closely spaced electrodes. The ratio of collector to generator current can thus be used to quantify tissue perfusion. To make the micron size ring-disc electrodes, a novel fabrication method was used. It relies on hollow cylindrical sputter coating and produces sensors with diameter as small as 28 μm. A number of numerical models of the sensor under diffusion and convection mass transport modes were constructed to assist the design process and to further our understanding of the behaviour of the electrodes in different situations. Experimental characterisation of the sensor was also carried out under diffusion and convection mass transport modes. These experiments also improved the design of the sensor and often agreed with numerical predictions. Finally the sensor was tested in a number of animal and human tissues as well as perfusion models. These were used as a proof of principle to confirming the capability of the sensor to continuously measure changes in tissue perfusion at the cellular level.