Effective Coupling of Light Emitting Diode to a Commercial Capillary Electrophoresis Laser-Induced Fluorescence Instrument for High-Sensitivity Analysis of Fluorescently Labeled Glycans

Light-emitting diodes offer a low-cost, power-efficient, and compact solution for fluorescence excitation in analytical instrumentation. This study discusses the coupling of a near-ultraviolet light-emitting diode (340 nm) to a commercial capillary electrophoresis instrument and presents two feasible strategies: a simple, robust, and low-cost option with moderate efficiency and a more complex but significantly more efficient design for applications demanding maximum sensitivity. The coupling efficiency was assessed using capillary zone electrophoresis of maltooligosaccharides labeled with the UV-excitable fluorophore, 6-[4-(4-methylpiperazin-1-yl)phenyl]pyridine-3-carbohydrazide. Compared to a commonly used indirect light guide coupling approach, the new direct coupling design, incorporating a single ball lens, provided a 10.7-fold increase in the fluorescence signal. The design incorporating two plano-convex lenses increased the fluorescence signal by a factor of 31.2 and achieved limits of detection between 99 and 105 nmol/L for the analyzed labeled maltooligosaccharides. This optimized configuration enabled the successful N-linked glycan analysis from minute sample quantities, specifically, 28.8 ng of ovalbumin and 7.49 ng of ribonuclease B.