Ultrasensitive cross correlation electrophoresis on microchip devices

Cross-correlation electrophoresis with fluorescence detection on a microchi p device was used to resolve a mixture of 63 pM fluorescein and 70 pM dichl orofluorescein. The signal-to-noise ratios of analyte peaks in a correlogra m derived from a 9-bit pseudorandom injection sequence were similar to 17 f or dichlorofluorescein and similar to 6 for fluorescein. In contrast, neith er peak was detected in a conventional electropherogram obtained on the mic rochip. Detection limits estimated from a correlogram derived from the aver age of 12 7-bit correlograms were 6.5 pM dichlorofluorescein and 21 pM fluo rescein. These are the lowest detection limits reported for a microchip sep aration device using analog detection and the first example of crosscorrela tion electrophoresis on a monolithic device. The small injection volumes, i njection reproducibility, and rapid separations enabled by microchip device s make cross-correlation multiplex injection schemes a viable approach for achieving enhanced sensitivity.