A novel on-chip optical flow cytometer concept is reported for fluorescence detection, enumeration, and sizing of microparticles in a poly-dimethylsiloxane (PDMS) microchip. The detection system integrates a pair of external optical fibers and other optical components for particle counting, sizing and fluorescence analysis in each measurement simultaneously. The scattered light signal indicates the total number and the size of the particles passing through the detection window, whereas the concurrent backward fluorescence signal shows only the number of fluorescence particles. In the experiments, microparticles of four different sizes with diameters ranging from 3.2 to 10.2 lm were discriminated and counted based on the fluorescence and scattered light intensity. The relative percentage of the fluorescence-labeled particles can be analyzed by the ratio of the events of fluorescence signals to forward scattered signals.

This paper deals with computational and experimental investigations into pressure-driven flow in sudden expansion microfluidic channels. Improving the design and operation of microfluidic systems requires that the capabilities and limitations of 2-dimensional (2-D) and 3-dimensional (3-D) numerical methods in simulating the flow field in a sudden expansion microchannel be well understood. The present 2-D simulation results indicate that a flow separation vortex forms in the corner behind the sudden expansion microchannel when the Reynolds number is very low (Re$0.1). However, the experimental results indicate that this prediction is valid only in the case of a sudden expansion microchannel with a high aspect ratio (aspect ratio >> 1). 3-D computational fluid dynamics simulations are performed to predict the critical value of Re at which the flow separation vortex phenomenon is induced in sudden expansion microchannels of different aspect ratios. The experimental flow visualization results are found to be in good agreement with the 3-D numerical predictions. The present results provide designers with a valuable guideline when choosing between 2-D or 3-D numerical simulations as a means of improving the design and operation of microfluidic devices.

This paper describes a novel concept of integrated on-chip fiber free laser-induced fluorescence detection system. The poly-dimethylsiloxane (PDMS) chip was fabricated using soft lithography and was bonded with a glass substrate of 150 lm thickness that reduced the distance of channel-to-sidewall to less than 180 lm. The cells and particles detection was conducted by an external single fiber close to the glass substrate that transmitted laser light for simultaneous excitation and receipt of the emission light signals. The performance of the proposed device was demonstrated using fluorescence beads, stained white blood cells, and yeast cells. The experimental results showed the simplicity and flexibility of the proposed device configuration which can provide convenient on-chip integration interface for fast, high throughput, and low-cost laser-induced fluorescence detection micro flow cytometer.