Devices that diagnose and characterize disease have the potential to greatly improve healthcare worldwide. This thesis explores a number of different elements pertaining to device design and application. A microfluidic device for the capture and profiling of circulating tumor cells (CTCs) is tested against a rabbit model of cancer. This device demonstrates both an increase in CTC load and aggressiveness which correlates with traditional computed tomography measurements. CTC biology is also shown to differ markedly from tumour precursor cells. Next, a study of gold microelectrode architecture is performed with the aim of improving performance towards biosensing. A unique regime of gold ion concentration, applied voltage, and electrolyte viscosity is determined which drives the assembly of a highly structured morphology. Further studies illustrate growth mechanisms and the sensitivity of the electrode towards biomolecule detection. Additionally, a microfluidic device for instrument-free manipulation of microscopic fluid quantities is developed. This design allows the metering and dispensing of reagents in an intuitive manner by combining a series of capillary valves and a simple push-button. This “Digit Chip” is applied to the detection of antibacterial susceptibility alongside a simple smart-phone based fluorimeter. Together these studies explore the application of electrochemical and microfluidic modalities to the realm of disease monitoring.