Microfluidic Probes and Quadrupoles: A new era of open microfluidics

The microfluidic probe (MFP) is a noncontact technology that applies the concept of hydrodynamic flow confinement (HFC) within a small gap to eliminate the need for closed microfluidic conduits and, therefore, overcome the conventional closed-system microfluidic limitation. Since its invention, the concept has experienced continuing advancement with several applications, ranging from manipulating mammalian cells and printing protein arrays to performing microfabrication. One of the recent developments of the MFP technology is the microfluidic quadrupole (MQ)-a microfluidic analogy of the electrostatic quadrupoles-that is capable of generating a stagnation point (SP) and floating concentration gradients. These distinct features combined with the open-channel concept make the MFP and MQ potentially suitable tools for studying cell dynamics or diagnostic cell trapping and manipulation (using the SP).