Polymer microchip CE of proteins either off‐ or on‐chip labeled with chameleon dye for simplified analysis

Microchip CE of proteins labeled either off‐ or on‐chip with the “chameleon” CE dye 503 using poly(methyl methacrylate) microchips is presented. A simple dynamic coating using the cationic surfactant CTAB prevented nonspecific adsorption of protein and dye to the channel walls. The labeling reactions for both off‐ and on‐chip labeling proceeded at room temperature without requiring heating steps. In off‐chip labeling, a 9 ng/mL concentration detection limit for BSA, corresponding to a ∼7 fg (100 zmol) mass detection limit, was obtained. In on‐chip tagging, the free dye and protein were placed in different reservoirs of the microchip, and an extra incubation step was not needed. A 1 μg/mL concentration detection limit for BSA, corresponding to a ∼700 fg (10 amol) mass detection limit, was obtained from this protocol. The earlier elution time of the BSA peak in on‐chip labeling resulted from fewer total labels on each protein molecule. Our on‐chip labeling method is an important part of automation in miniaturized devices.