ABSTRACT
Miniaturization of flow cytometry is of fundamental importance in point-of-care and personalized diagnostics. Conventional flow cytometry is a standard analytical method in cell biology, but restrictive due to its high price, complexity, and large size. To address miniaturization needs, a number of investigators in microfluidics, lab-on-a-chip, and bio-microelectromechanical systems have focused on the development of microflow cytometers using microfluidic technologies and miniaturized optical components. This chapter provides a review of the methods for focusing particles without sheath flows in microfluidic devices. These methods include field-based techniques that use external forces such as dielectrophoresis, acoustic, and optical forces, and flow-assisted techniques that exploit hydrodynamic phenomena such as inertial lift forces, hydrodynamic filtration, deterministic hydrodynamics, and hydrophoresis. The chapter describes details of the focusing principles and their application to flow cytometry, comparing their advantages and disadvantages. It presents some challenges and future trends of microfluidic technologies for sheathless particle focusing.
