Toward a sensor platform combining three-dimensional electrochemical arrays and microfluidics

Abstract

Detection and sample handling are two critical components in the miniaturisation and future automation of biochemical sensors. However, up until now, the mass production of these sensor devices has been expensive, with devices typically being restricted to academic settings. This thesis concerns the design of a highly sensitive three-dimensional electrochemical sensor within a re-usable microfluidic device. The work developed here proposes a generic platform, which has been demonstrated, by a combination of multidisciplinary fabrication and surface modification techniques, to provide cost-effective miniaturisation without compromising sensitivity. This thesis can be broken into four parts. The first section explores the possible application of hydrodynamic focusing to selectively functionalise a three-dimensional surface. Commercial multi-physics COMSOL software was used to simulate and develop the fabricated hydrodynamic focusing device. A convergent bonding fabrication technique was then utilised for the integration of three-dimensional electrodes for the purpose of multiplexing on a spatiotemporal scale. We then examined differential current density distribution as a means of controlling selective functionalisation at the apices of three-dimensional electrodes. A combination of fabrication methods were used to produce a cost-effective and uniform three-dimensional pyramidal electrodes. Differential current distribution density was then demonstrated with surface modification techniques with a variety of species including redox active molecules, fluorophores, oligonucleotides and nanoparticles for selective functionalisation. This versatile approach opens the door to a number of applications in biosensors and electrocatalysis. Particle synthesis was then extended in the subsequent section by using a self-assembled monolayer for template assist deposition. The particle size and population could be controlled based on the carbon chain length and the terminal group of the monolayer to serve as a platform to electrodeposit the desired platinum particles. In addition, fundamental nucleation mechanisms were studied to understand factors involved in the molecular diffusion and thermodynamics of redox reactions. Based on all experimental results considered, pyramidal array electrodes were further modified to produce pyramidal microelectrode array. A simple lithographic technique demonstrated the feasibility of fabricating these pyramidal microelectrode arrays, which were comparable to commercially available products. The final section presents the integration of this pyramidal microelectrode array into a simple re-usable microfluidic system, demonstrating a highly sensitive biochemical sensor capable of mass production.