LIFGO: A modular laser-induced fluorescence detection system based on plug-in blocks.

In this work, a laser-induced fluorescence (LIF) detection system built in a modular assembling mode was developed based on commercial LEGO blocks and 3D printed blocks. We designed and fabricated a variety of 3D printed building blocks fixed with optical components, including laser light source, filters, lens, dichroic mirror, photodiode detector, and control circuits. Utilizing the relatively high positioning precision of the plug-in blocks, a modular construction strategy was adopted using the flexible plug-in combination of the blocks to build a highly sensitive laser-induced fluorescence detection system, LIFGO. The LIFGO system has a simple structure which could be constructed by inexperienced users within 3 h. We optimized the structure and tested the performance of the LIFGO system, and its detection limits for sodium fluorescein solution in 100 µm i.d. and 250 µm i.d. capillaries were 7 nM and 0.9 nM, respectively. Based on the LIFGO system, we also built a simple capillary electrophoresis (CE) system and applied it to the analysis of DNA fragments to demonstrate its application possibility in biochemical analysis. The separation of 7 fragments in DL500 DNA markers were completed in 600 s. Because of the features of low cost (less than $100) and easy-to-build construction, we introduced the LIFGO system to the experimental teaching of instrumental analysis for undergraduate students. The modular construction form of the LIF detection system greatly reduces the threshold of instrument construction, which is conducive to the popularization of the LIF detection technique in routine laboratories as well as the reform of experimental teaching mode.

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 mm3, 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.