Bi-enzymatic and capillary electrophoretic analysis of non-fluorescent compounds in microfluidic devices: Determination of xanthine

This report describes general investigations for xanthine determination in microfluidic devices. Xanthine is chosen as a model analyte for the detection of compounds via bi-enzymatic systems on one hand, and via capillary electrophoresis (CE) of non-fluorescent analytes on the other. The bi-enzyme system comprises xanthine oxidase (XOD) and horseradish peroxidase (HRP) with XOD giving the specificity for the analyte and HRP allowing chemiluminescent (CL) detection. Studies include the use of enzyme solutions, as well as enzyme coated beads pumped continuously through the device or trapped in a 330 pL cavity. In a second approach, indirect laser-induced fluorescence (LIF) is used as a detection method for microchip-based CE separations. Although the detection methods are not optimised, this report demonstrates general new possibilities for a fast determination of such compounds, in particular xanthine, in microfluidic devices.