Doctor of Philosophy (PhD)
Solid phase extraction (SPE) is a widely used method to separate and concentrate the target molecules in liquid mixture. Traditional SPE has to be conducted in the laboratory with professional equipment and skilled operators. The microfluidic and 3D printing technology have opened up the opportunity in developing miniaturized automatic instruments. The main contribution of this research is to integrate the SPE process on a novel centrifugal platform. Various valves are applied on the platform to help control the aqueous sample and reagents in the cartridge.
First, a centrifugal microfluidic platform was built for automatically detecting trace oil pollution in water. Mechanical valves were used to control the flow of the reagents and water sample in the device. The prototype of the proposed system was fabricated using 3D printing technology and tested with 10ppm standard oil-water mixing sample. Different stationary sorbents were tested and compared and the 3D printed porous polymer showed the best performance. The experimental results had proved that the detection sensitivity of the water-oil mixture sample can be significantly enhanced after it was enriched using the centrifugal microfluidic platform.
Then, a truly three-dimensional (3D) microfluidic cartridge for SPE was fabricated and tested on the centrifugal platform. A novel gravity valve was designed and applied in the centrifugal cartridge. Unlike the traditional capillary valves, which can only be sequentially opened via increasing the spinning frequency, the gravity valve was more flexible. Gravity valves, traditional capillary valves, and Coriolis switching valves were integrated in one cartridge to manipulate reagents and the sample involved in the SPE process. All the valves can be simply controlled by the rotating direction and speed of the cartridge. The prototype microfluidic cartridge was 3D printed and experimentally tested. Anthracene, which was one of the Polycyclic Aromatic Hydrocarbons (PAHs), was used as the target analyte and tested with the presented design. C18 was used as the stationary sorbent and fluorescence method was adopted to detect anthracene. The original testing samples of anthracene were 1 µg/L (1ppb), 5 µg/L, and 10 µg/L (anthracene/water), respectively. The volumes of testing sample and eluent (nonane) were 10 mL and 1 mL respectively. Experiments showed that the prototype device performed well and fluorescence intensities after SPE were 7 to 11 times of the original sample. Perylene of 1 µg/L (perylene/water) was also tested on the platform and the integrated fluorescence intensity after SPE was 8.3 times of the original sample.
Finally, solid phase extraction and fluorescence detection experiments were conducted for the crude oil- containing seawater samples using the prototype device. Oil-seawater samples with oil concentrations of 10 ppm, 5 ppm, and 2 ppm were prepared respectively. The volumes of oil-seawater mixed sample and eluent (nonane) were 10 mL and 1 mL respectively. The integrated fluorescence intensities of the eluent after SPE were measured to be about 4.8 to 6.9 times of the oil-water mixed samples. More importantly, the SPE process eliminated the interference of the CDOM in the seawater.
Zhang, Yong, "Centrifugal Microfluidic Platform for Solid-Phase-Extraction (SPE) and Fluorescence Detection Applications" (2020). LSU Doctoral Dissertations. 5397.