Sorter Design

Subsequent work in this laboratory has been on the development of a continuous, stream-centered DEP cell sorter/analyzer. There are certain problems inherent in sorting cells that are not encountered in sorting minerals, for example. 

FIGURE 12. The lateral deflection, in microns after 2.5 cm travel of the live yeast, Saccharomyces cerevisiae in the automated DEP spectrum analyzer. Resistivity, 300kI2cm. Voltage, 2.5 V rms. 

FIGURE 13. The lateral deflection of dead yeast in the automated DEP spectrum analyzer conditions as in Fig. 12 above, but at 120 kCI cm. 

A DEP cell sorter/analyzer has been developed which uses the polarizability of cells to characterize and sort them. All types of cells (algae, bacteria, mamalian) can be handled easily by DEP. This technique gives the biologist a new tool to both characterize and handle cells. 

Dielectrophoresis, The Behavior of Matter in Nonuniform Electric Fields, Cambridge University Press, Cambridge (1978). 

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Among the items that have been measured are vitality, intracellular pH, DNA and RNA content, and specific plasmids [77,408]. Besides nucleic acids [204], other intracellular components can also be analyzed, e.g. storage materials [2, 82,294], enzymes and protein content [6,338], or the cell size [60,61]. The physiological state can also be rapidly assessed [331]. Furthermore, this technique allows the separation of certain cells using a cell sorter, e.g. for strain improvement [28]. The flow cytometry technique has also been used in connection with molecular probes for identification and viability determination of microbial communities [98]. This application of viability estimation is becoming increasingly important [63, 136, 188, 454]. Unfortunately, the equipment is expensive and most of the measurements are tricky and laborious and not well designed for on-line application. 

Downstream sorting is used, and the design of the sorting system limits the number of orders that may be in process at one time. Note that the number of orders in process can often exceed the number of output chutes of a conveyor sorter (Bozer et al. 1988). 

Optical sensors can be used to separate plashes based on either color or transparency. This technique is used to separate bottles by color because clear PET has more value than colored PET. Developed from the coffee bean separators that are used to eliminate unripe green beans from the mix, these computer-controlled systems can rapidly differentiate between the various hues of the plastic regrind. The color of each piece of plastic is quickly established using a type of CCD camera and is either allowed to flow downward or is ejected with a puff of air into the reject or collection pile. Satake [77], for example, produces equipment that is specifically designed to separate plastics by color but their main business is still from the agricultural industry. Satake s ScanMaster IE, SE, and DE Optical Sorters are used to differentiate the colors of HDPE and PET materials in recycling operations. 

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