Flow cytometry hydrodynamic

The technical term for this is hydrodynamic focusing, flow of a sample stream within the center core of a sheath stream is called coaxial flow. The exact diameter of that central sample core within the sheath stream is related to, among other things, the rate at which the sample is injected into the sheath stream a 100 pm sheath stream may, depending on sample injection velocity, have a core width of perhaps 5-20 pm (Fig. 3.4). Because hydrodynamic focusing tends to confine the cell sample to this central core, there is little mixing of sample with sheath fluid (but diffusion of small molecules will occur). The reason that this type of coaxial sample flow suits flow cytometry... 

Flow cytometry is a very versatile technique [223] which allows the analysis of more than 104 cells per second [369,370]. This high number results in statistically significant data and distributions of cell properties. Therefore, flow cytometry is a key technique to segregate biomass (into distinct cell classes) and to study microbial populations and their dynamics, specifically the cell cycle [76, 87, 116, 200, 214, 221, 295, 329, 330, 409, 418]. Individual cells are aligned by means of controlled hydrodynamic flow patterns and pass the measuring cell one by one. One or more light sources, typically laser(s), are focused onto the stream of cells and a detection unit(s) measure(s) the scattered and/or fluorescent light (Fig. 24). Properties of whole cells such as size and shape can be... 

Sundararajan N, Pio M, Lee L, Berlin A (2004) Three-dimensional hydrodynamic focusing in polydimethylsiloxane (PDMS) microchannels. J Microelectromech Syst 13(4) 559-567 Yang R, Feeback D, Wang W (2005) Microfabrication and test of a three-dimensional polymer hydro-focusing unit for flow cytometry applications. Sens Actuators A Phys 118(2) 259-267... 

Sheath-flow cuvettes were originally developed for flow cytometry, but were adapted for use with CE by Dovichi. " Figure 20.16 illustrates LIF detection in conjunction with a sheath-flow cuvette. As displayed, the capillary is surrounded by sheath-flow buffer inside the cuvette. As organelles migrate out of the capillary, they are hydrodynamically focused by the sheath flow into a narrow stream. The excitation source is focused beneath the capillary outlet to excite the organelles once they have been focused. Since the diameter of the sample stream is dependent on the difference between the volumetric flow rates of the sample stream and the sheath flow, the sample stream can be narrowed to the desired width by increasing the sheath volumetric flow. 

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