Doctor of Philosophy (PhD)


Engineering Science

Document Type



Centrifugal microfluidics has emerged as a reliable and proven technology with a wide range of applications in various fields, including clinical chemistry, immune-diagnostics, molecular diagnostics, food, water, oil spill, and soil analysis. Nowadays, exploring the possibilities of centrifugal microfluidics is a hot research topic. Enzyme-linked immunosorbent assay (ELISA) is increasingly gaining popularity due to its high sensitivity, accuracy, and visual results. ELISA has become a gold standard tool for clinical diagnostics. Moreover, efficient mixing is often a critical step in sample dilution, chemical reactions, bioassays, and medical analysis. An effective mixing process accelerates the speed of reaction, enhances system sensitivity, and even significantly impacts the distribution of final product. Particularly, mixing is a crucial step in competitive ELISA. In this study, lab-on-a-CD immunoassay systems were designed, fabricated using FDM 3D printing technology, and tested. The centrifugal platform mainly consisted of a motor and a high-speed camera.

In the initial phase of the study, A 3D printing technology was utilized to design and create an impingement micromixer with arrays of micronozzles, also known as jet micromixer, obtaining better efficiency. This innovative mixer significantly enhanced the interfacial area of two different liquids by utilizing colliding plumes generated from two opposing sets of micronozzles, resulting in superior mixing effect. The mixing performance of the jet mixer was evaluated in contrast of the widely employed Y-shaped micromixer. Remarkably, effective mixing was achieved within a remarkably short duration of just 3 seconds. The 3D printed jet mixer holds immense potential for integration into diverse 3D printing equipment utilized in microfluidic platforms for various practical applications.

The second part of the paper introduces a novel, simple, and powerful 3D-printed mixing device, called the gravity mixer, for centrifugal microfluidic platforms. The mixer features a slope structure that allows for accurate and sequential control of micro-volume liquids by using capillary, centrifugal and gravitational forces, enabling efficient mixing. By controlling the slope geometry, micro-volumes of liquids in the mixer can be manipulated across a broad spectrum of rotational speeds. The study investigates the effect of slope geometry, such as the angle of the slope and the number of mixing cycles, on the mixing efficiency. The results show that the sharpest slope mixer (with the maximum angle) achieves the best mixing efficiency, with a standard deviation of 2.39. The design and implementation of the gravity mixer offers a potential for developing complex 3D printed lab-on-chip devices.

In the third part of our study, firstly we developed a microfluidic cartridge on a compact disk (CD) for immunoassays based on FDM 3D printing and LCD 3D printing. Based on FDM 3D printing as FDM microfluidic CD, the microfluidic CD was fabricated using transparent Polycarbonate (PC) as the structural material. To ensure precise control of the immunoassay system, we incorporated three capillary and mechanical valves to regulate the fluids’ sequence. Based on LCD 3D printing as LCD microfluidic CD, the microfluidic CD was fabricated using clear photopolymer resin as the printing materials. The microfluidic CD design combined the capillary valve, hydrophobic valve with siphon valve to control the sequence of liquids’ release. The microfluidic unit operations in the cartridge included sample preparation, incubation, washing, mixing, detection, and waste disposal. As the model application, we tested the feasibility of the proposed devices (microfluidic CD based on FDM 3D printing and LCD 3D printing) for immunoassay applications by performing a competitive chemiluminescent estradiol immunoassay with a series of different estradiol concentrations. Then, we compared the results between the microfluidic devices. This shows the automatization of conducting ELISA detection and be realized and it has the high potential to realize the application in point of care testing (POCT).



Committee Chair

Dr. Wanjun Wang

Available for download on Wednesday, August 14, 2030