Miniaturized Absorption Spectrometers And Its Applications

After twenty years'development, microfluidics has been perceived as one of the most promising revolutionary technologies for on-site analysis and point of care testing (POCT) for its advantage of low sample consumption, rapid analysis, automation and miniaturization of device. Nevertheless, there are still two challenges in the miniaturization of absorption detection systems, including the short path-lengths in miniaturized systems constraining the detection sensitivity, and the lack of fully-integrated absorption spectrometers involving absorption detector, controlling circuit and fluid-handling device.In Chapter One, the development and the recent progress of long path length microfluidic absorption detection systems are reviewed. The fluid driving techniques and reagent preloading techniques suitable for point of care application are also introduced.In Chapter Two, a fully integrated hand-held photometer based on the liquid-core waveguide (LCW) detection principle for nanoliter-scale samples was developed. All components of the photometer including light-emitting diode (LED) light source, LCW flow cell, photodiode detector, dropper pump, electronic circuit, liquid-crystal display screen, and battery were fully integrated into a small-sized (12 x 4.5 x 2.1 cm) instrument. A bent optical coupler was developed to conduct the detection light into or out of the LCW flow cell through its sidewall. This design allowed the sampling probe, input and output optical couplers, and LCW flow cell to be integrated in a single Teflon AF capillary, which significantly simplified system structure, improved working reliability, and reduced sample consumption. Two UV-LEDs were used as light source in the photometer to achieve dual wavelength detection at 260 and 280 nm, which was applied to assess on-site the quality and quantity of DNA samples. The effective optical path length of the photometer was-15 mm with a sample consumption of only 350 nL. The potential of the photometer applied in POCT was also demonstrated in the measurement of total cholesterol in serum samples.In Chapter Three, a totally-integrated handheld photometer based on multi-reflection principle for POCT was developed. The photometer consists of a disposable multi-reflection flow cell, a permanent absorption detector and a dropper pump. The disposable multi-reflection flow cell was composed of a fused silica capillary with specular paint coating. The effective optical path length of the multi-reflection flow cell was -8 mm with a detection volume less than 400 nL. The capillary was also functioned as a liquid cartridge which was preloaded with plugs of reagents segmented by oil. A series of operations including liquid metering, introducing, mixing and driving were realized using the dropper pump, to achieve photometer calibration, and absorbance measurements of sample and standard solutions. The present photometer has advantages of low cost and no cross contamination between different samples, and has potential in the application of POCT.