Ultralow Detection Limits for an Organic Dye Determined by Fluorescence Spectroscopy with Laser Diode Excitation

Fluorescence of IR-140, a laser dye in methanol solution, is excited by a semiconductor laser diode. Analytical figures of merit are compared for three different instrumental configurations, with the dye measured in a cuvette, a liquid Jet, and a compact instrument. The best limit of detection, 46 000 molecules, was achieved with a liquid Jet. Linear dynamic range was 6 orders of magnitude. The laser diode operates in the near-Infrared region, resulting in low background fluorescence.