Single-use, Multichannel Microfluidic Chips for CE

微流控技术的发展及其在生物医学检测中的应用有可能提高许多广泛使用的技术的质量和通量。特别是，基于微芯片的毛细管电泳可以产生更快的分析时间，更低的试剂消耗和更易于使用的硅胶毛细管电泳。然而，更常用的玻璃微芯片制造成本昂贵，并且可能不适合交叉污染问题和需要一次性设备的应用。相比之下，塑料或聚合物微流控芯片可以用热压或注射成型技术制造，每个芯片只需要几美分。然而，激光诱导荧光检测在聚合物微芯片提出了一些独特的挑战。由于塑料衬底比独立的二氧化硅毛细管具有更强的荧光性，因此需要空间选择性检测来隔离来自通道内的荧光信号，以达到所需的灵敏度。在过去，这需要一个共聚焦系统，通过对光学元件的机械扫描来测量多个通道。

The development of microfluidic technology and its application to biomedical assays has the potential to improve the quality and throughput of many widely used techniques. In particular, microchip-based capillary electrophoresis could yield faster analysis times with lower reagent consumption and greater ease of use than CE in silica capillaries. However, the glass microchips more commonly used are expensive to manufacture, and can be ill-suited to applications for which cross-contamination is an issue and single-use devices are desired. In contrast, plastic, or polymeric microfluidic chips can be manufactured with hot-embossing or injection molding techniques for pennies per chip. However, laser-induced fluorescence detection in polymeric microchips presents some unique challenges. Because the plastic substrate is substantially more fluorescent than freestanding silica capillaries, spatially selective detection is required to isolate the fluorescent signal originating from within the channel in order to achieve the desired sensitivity. In the past, this has required a confocal system, with the measurement of multiple channels achieved by mechanical scanning of the optical elements. We have developed and demonstrated a new scheme for sensitive, spatially selective and spectrally resolved laser-induced fluorescence detection from multiple microfluidic channels, and applied this scheme to 10 Hz five-color forensic DNA analysis in a polymeric microfluidic device. Free-space 488 nm laser excitation is spread into a collimated line with two cylindrical lenses and then split into multiple focused spots using an array of spherical plano-convex lenses with diameters equal to the microchannel spacing. At each excitation spot, a ball lens and an optical fiber is positioned underneath the microchannel. The spatial selectivity is achieved by using a high refractive index ball lens and a substantially smaller-diameter optical fiber positioned to obtain focused light from the channel. The detection optics can be freely positioned near each channel, placing minimal constraints on channel layout and design. The other ends of the optical fibers are formed into a 1-D array and directed onto the entrance slit of an imaging spectrograph. Analysis of standard DNA base-pair ladders in an eight-channel configuration shows comparable sensitivity to that obtained with measurements of a single channel using a commercial confocal microscope. Although this technology has been evaluated using short-tandem repeat DNA separations, the instrument can easily be used for most multi-color, multi-channel CE analyses. In particular, we plan to explore the possibilities for multiplexed free-zone CE immunoassays within the next year. The prototype instrument is robust, versatile, contains only fixed optical parts, and has the potential to be more cheaply implemented than competing technologies. The economies of parallel detection and the importance of spatial selectivity make this method generally useful for separations in polymeric substrates with multiple microchannels.