Microfluidic inertial focusing has been demonstrated to be an effective method for passively positioning microparticles and cells without the assistance of sheath fluid. Because inertial focusing produces well-defined lateral equilibrium particle positions in addition to highly regulated interparticle spacing, its value in flow cytometry has been suggested. Particle focusing occurs in straight channels and can be manipulated through cross sectional channel geometry by the introduction of curvature. Here, we present a staged channel design consisting of both curved and straight sections that combine to order particles into a single streamline with longitudinal spacing. We have evaluated the performance of these staged inertial focusing channels using standard flow cytometry methods that make use of calibration microspheres. Our analysis has determined the measurement precision and resolution, as a function of flow velocity and particle concentration that is provided by these channels. These devices were found to operate with increasing effectiveness at higher flow rates and particle concentrations, within the examined ranges, which is ideal for high throughput analysis. Further, the prototype flow cytometer equipped with an inertial focusing microchannel matched the resolution provided by a commercial hydrodynamic focusing flow cytometer. Most notably, our analysis indicates that the inertial focusing channels virtually eliminated particle coincidence at the analysis point. These properties suggest a potentially significant role for inertial focusing in the development of inexpensive flow cytometry-based diagnostics and in applications requiring the analysis of high particle concentrations.

Flow cytometry can simultaneously measure and analyze multiple properties of single cells or particles with high sensitivity and precision. Yet, conventional flow cytometers have fundamental limitations with regards to analyzing particles larger than about 70 microns, analyzing at flow rates greater than a few hundred microliters per minute, and providing analysis rates greater than 50,000 per second. To overcome these limits, we have developed multi-node acoustic focusing flow cells that can position particles (as small as a red blood cell and as large as 107 microns in diameter) into as many as 37 parallel flow streams. We demonstrate the potential of such flow cells for the development of high throughput, parallel flow cytometers by precision focusing of flow cytometry alignment microspheres, red blood cells, and the analysis of CD4+ cellular immunophenotyping assay. This approach will have significant impact towards the creation of high throughput flow cytometers for rare cell detection applications (e.g. circulating tumor cells), applications requiring large particle analysis, and high volume flow cytometry.

Effective methods for manipulating, isolating and sorting cells and particles are essential for the development of microfluidic-based life science research and diagnostic platforms. We demonstrate an integrated optical platform for cell and particle sorting in microfluidic structures. Fluorescentdyed particles are excited using an integrated optical waveguide network within micro-channels. A diode-bar optical trapping scheme guides the particles across the waveguide/micro-channel structures and selectively sorts particles based upon their fluorescent signature. This integrated detection and separation approach streamlines microfluidic cell sorting and minimizes the optical and feedback complexity commonly associated with extant platforms.