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.