A compact and highly sensitive light-emitting diode-induced fluorescence detector for capillary flow systems

A compact and highly sensitive light-emitting diode-induced fluorescence detector (LED-FD) was constructed and evaluated. The LED excitation beam was restricted by a 200 μm diameter pinhole on a 55 μm thick lighttight film. The LED, excitation filter, pinhole, and capillary flow cell were placed tightly against each other without either optical lens or excitation fiber. The performance of the LED-FD was evaluated by flow injection analysis (FIA) of sodium fluorescein solution. The limit of detection (LOD) was determined as 0.75 nM (SNR = 3). Compared with our previous work, a 3.5-fold enhancement on the signal-to-noise ratio (SNR) was obtained. The system exhibited linear responses in the concentration range of 2–200 nM (R = 0.9993). The error of repeatability was within 2.0% R.S.D. on peak height in a ten-repeated injection of 5 nM solution. The reproducibility between devices was within 2.2% R.S.D. on peak height of 10 nM fluorescein solution. Finally, the LED-FD was compared with commercial fluorescence detector, and similar fluorescence signal intensity was obtained.