The Design Of Semiconductor Solid-State Light Sources Induced Fluorescence Detection For Flow Analysis System

Laser-induced fluorescence detection (LIF-D) is one of the most sensitive methods developed so far in the world. The concentration of lowest detection limits (known as CLODs) of the best CE/LIF systems usually fall into the range of 10-9 to 10-12M. LIF-D is the most commonly applied detection method for the determination of trace components in environmental and biological samples. The limitations in high sensitive LIF-D systems result from bulky size, high cost and complicated optical structures. These characteristics make the traditional detectors incompatible with the alleged microscale separation techniques. It is, therefore, interesting to develop compact and portable LIF-D for flow analysis systems such as HPLC, FIA, CE and μ/TAS.A compact LIF-D system, based on laser diode (LD) emitting at 635nm as excitation source and confocal optical configuration, was developed and evaluated. Parameters affecting the detection sensitivity and reproducibility were investigated. The GLOD of the detector was 3.7nM by using Cy5 as fluorophore. The performance is comparable to that of the commercial detectors and the data in literatures.Two types of LD-DPSSL emitting at 532nm and 473nm were used as excitation source for the construction of portable LIF-D based on confocal optical configuration. Modular design is adopted for the LIF-D, in which a separate flow cell module is inter-changeable according to the application. When the LIF-D is used for differentflow analysis system, such as HPLC, CE or TAS, only the flow cell module needs to be changed. The CLOD of Rh B and FITC was 0.3 nM and 5pM, respectively. A novel flow cell for HPLC was designed in the confocal LIF-D. It has the advantages of low extra-column diffusion effect, easy machining and easy changeable.A miniaturized fluorometer was constructed and evaluated using light emitting diode (LED) as excitation source. In this configuration, an optical fiber was used to collect the fluorescence and the combination of lens and aperture was utilized to realize the effective coupling between the excitation source and capillary flow cell. To overcome the difficulty of optical alignment for the on-column detection scheme, a simple and effective optical alignment device was designed. Three measures were taken to enhance the sensitivity of LED-induced fluorometer, including the pulse current drive and the reduction of the thickness of the dome to increase the effective light output of LED, the ball shaped head of optical fiber to improve the efficiency of fluorescence collection, and the decrease of background scatter light. The concentration and mass detection limits observed for fluorescein were 1.8 x 10-7 mol/L and 4.3 fmol, respectively. The optical alignment in on-column fluorescence detection can be effectively carried out by a T-shaped device. Some novel fluorometer-based different detection cell was also constructed.