Microfluidics has emerged as a technology with significant impact on medical research and clinical applications. The abilityto manipulate fluids at the microscale has led to innovative and powerful techniques to manipulate and study cells at thesingle cell level. This talk will cover three different microfluidic systems that we developed to study different biological systemsat the single cell level. The first system intended to study cancer cell survival and death following stimulation with Tumor NecrosisFactor (TNF). Using the system, cells were selectively exposed to brief pulses of TNF, as short as 8 s. We studied the survivaland death pathways in cells, and preliminary results suggested that short pulses of TNF stimulation can provoke early cancercell death. The second system is the Microfluidic Quadrupole (MQ), which constitutes the first experimental demonstrationand characterization of fluidic quadrupoles. We used the MQ to manipulate concentration gradients of Interleukin-8 atop humanneutrophils cultured in Petri-dishes. We challenged neutrophils with stationary and moving gradients and studied theirdynamics during adhesion, polarization, and migration. Finally, I will discuss our recent experiments in using the microfluidictechnology to capture circulating tumor cells from blood samples taken from cancer patients.