Handheld laser-induced fluorescence detection systems with different optical configurations.

There is a growing urgent requirement for miniaturized laser-induced fluorescence (LIF) detection systems in many research fields. In this work, miniaturized LIF detectors with three different optical configurations of orthogonal, confocal, and oblique were developed, using a laser diode as the excitation source and a photodiode as the photodetector. The computer simulation and experimental methods were used to investigate the distributions of laser scattered light and fluorescent light near the detection window. Other conditions including the solution preparation, sample flow rate, alignment method and filter model were also optimized. Under the optimized conditions, the detection limits of sodium fluorescein for orthogonal and confocal LIF detectors were 40 pM and 50 pM, respectively, while the limit of detection (LOD) for oblique LIF detector were 1 nM (45°) and 7 nM (67.5°). We further built a fully integrated handheld orthogonal LIF detector with a total size of 50 × 20 × 46 mm, a cost of $380, and a detection limit of 10 pM for sodium fluorescein. It is expected that such a LIF detector could be applied in field analysis as a portable instrument or in other analysis systems as a detection module.