Carbon-based microfluidic impedance cytometry

Abstract

Microfluidic Impedance Cytometry (MIC) is a powerful sensing technique for single-cell electrical analysis and discrimination. It involves applying AC voltage to two or more pairs of electrodes to measure the change in impedance as single particles pass by. This method has been used to analyse various micro-organisms, blood cells, and animal and human cell lines. The development of MIC holds promises for the integration of flow cytometry with wearable hardware and mobile processing, paving the way for a user-friendly system for continuous and remote diagnosis. In this work the traditional coplanar electrode configuration is used, and the electrode material is changed from metal electrodes to carbon-based such as graphene and Pyrolytic carbon. Results are presented for gold, graphene, and Pyrolytic carbon electrodes as part of a complete microfluidic detection system. a) Experimental investigations on the MIC device with gold coplanar electrodes provide valuable insights into particle detection and behaviour. Controlled experiments with varying channel heights and electrode separations demonstrate the crucial balance between sensitivity and fluid dynamics, with 30μm Au electrode separation emerges as the optimal choice, boasting the highest sensitivity of 4.97 × 10−8 . Subsequently, analysis of 10μm and 20μm particle mixtures highlights the challenges and successes in distinguishing particle sizes. b) A novel approach to fabrication of the pattern graphene electrodes and a method for integration with a microfluidic channel is presented. A comprehensive study then addresses the challenges in preserving the integrity of graphene electrodes. MIC measurements with graphene electrodes presents unique challenges emphasizing the need for precise optimization in surface treatments and protective coatings. c) Microstructured Pyrolytic carbon are integrated with an equivalent MIC device to optimization, Study shows that using a modified electrode separation of 50𝜇𝑚 leads to a promising sensing result. Optimized Pyrolytic carbon electrodes are shown to provide a sensitivity of 2.29 × 10−8 under testing. In closely related work, two-photon subtractive manufacturing is explored for use in microfluidic channel fabrication where feature definition of 50𝜇𝑚 × 50𝜇𝑚 was demonstrated for common polymeric materials PMDS, PMMA, PS and PC. Feature fabrication at depths below 1mm were discovered and the ability for versatile subsurface patterning opens up a host of exciting future work.