Polymer Lab-on-a-Chip System With Electrical Detection

Two important challenges of the rapid development of microfluidic chip systems are addressed in this paper: 1) new polymer materials and technologies for chip preparation and 2) a label-free method for analyte detection in microchannels. One of the general pacemakers in lab-on-a-chip concepts, capillary electrophoresis (CE) in chip format, was used as workhorse for demonstration. CE chips were fabricated and characterized using polymers such as PMMA, polystyrene and polycarbonate, cycloolefine copolymer, and for the first time, the outstanding high-performance polymer polyether ether ketone (PEEK). Especially for one of the most critical steps in microchannel preparation, bonding of the cover layer to the microstructured substrate, an advanced plasma preconditioning process has been developed. An electrical detection method, capacitively coupled contactless conductivity measurement (CCD), was transferred to the chip level. A high signal-to-noise ratio was obtained by using sputtered thin-film electrodes. It was additionally improved by the very thin channel cover layer thickness, which could be easily obtained by polymer technology. CCD was used for analyte detection near the outlet of the CE separation channel. Further, to demonstrate generally the benefit of CCD for microfluidic flow control, measurement electrodes were positioned at the CE chip injection cross to monitor the reliability of the sophisticated injection processes. A completely miniaturized CE device (ldquoMinCErdquo), was developed for low cost application. Potential applications were demonstrated on selected typical examples: for in situ food analysis, the determination of saccharides in beverages, for medical point-of-care diagnostics, the quantitative determination of antidepressant lithium in blood serum, and for bio analytics, the detection of proteinogenic amino acids. Biological macro molecules-in particular, for life sciences fundamental DNA-have not been in focus of contactless conductivity measurements until now. However, it was possible for the first time to detect DNA highly sensitive by conductivity measurement. The extremely low detection limits achieved are competitive with laser induced fluorescence (LIF) in commercial CE-chip-devices and could provide a highly cost-efficient alternative.