Manipulation of biological cells with optical tweezers and lab-on-chip technologies

Abstract

Accurate sorting and manipulation of specific live cells from a small amount of heterogeneous samples are ubiquitous in biological research and clinical medicine. In this study, a generic cell manipulation system that integrates optical tweezers and labon- chip technologies is established, which can be further combined with the developed enhanced cell sorting strategy to realize automatic cell isolation with high accuracy. In addition, a novel cell manipulation tool is developed, which enables many different kinds of techniques for further analysis or manipulation, such as cell recognition, isolation, transportation, and deposition, to be carried out. This thesis includes the following aspects. First, a cell manipulation system for cell isolation and transfer is set up with integrated optical tweezers and microfluidic chip technologies. The sample flow can be driven into the microfluidic chip designed for different applications. Real-time image processing techniques, based on either the intrinsic features, such as cell size, or the extrinsic features, such as fluorescent labels, are developed to recognize the target cells. Calibration of the optical trap is performed to realize robust cell manipulation without cells escaping from the trap. Cell transfer can be achieved by employing single, as well as multiple optical traps, in different regions of interest (ROI). Experiments on yeast cells are performed to test the feasibility of the established system. Second, with the established cell manipulation system, an enhanced cell sorting strategy based on dynamic fluid and dynamic light pattern is developed to isolate rare cells with high recovery rate and high purity. A microfluidic chip with an aqueous two-phase laminar flow is designed for transporting the sample flow and buffer flow separately. The multi-particle tracking algorithm is utilized in the image processing module to distinguish the recognized target cells to optimize the multi-particle parallel sorting process in the same ROI. The motion dynamics of the optical trap in the fluid flow is further analyzed to separate the target cells successfully from the sample flow to the buffer flow. Experiments on the sorting of yeast cells and human embryonic stem cells (hESC) have been performed to demonstrate the effectiveness of the proposed enhanced cell sorting strategy. Third, with the microwell array-based lab-on-chip design, an automatic cell manipulation tool is developed to perform a series of cell manipulation tasks, including target cell recognition, cell levitation, cell transportation to the desired locations, and cell deposition. Unlike traditional microfluidic flow cytometry, this tool allows the cells to be inspected over a period of time in microwells with high spatiotemporal resolution, which makes it more suitable for cell isolation based on complex phenotypes. Furthermore, this tool allows for dynamic and parallel cell manipulation with multiple independent optical traps at the single-cell level, which helps improve manipulation flexibility and productivity. Moreover, the tool can precisely transfer the assembled target cells to the other predefined microenvironments, which can be combined with other on-chip functionalities for further analysis or manipulation. Finally, the experiments on the hESC lines are performed to test the effectiveness of the developed tool. In summary, the proposed cell manipulation tools with combined optical tweezers and microfluidic lab-on-chip technologies can achieve automatic and dynamic cell manipulation and isolation, with unique advantages of high recovery rate and high purity, especially in handling small cell populations. This tool will be particularly useful in applications where the cells of interest, such as stem cells or primary cells, are rare and difficult to obtain. The other on-chip functionalities can be easily integrated with the developed tools for different kinds of cell manipulations without removing the cells from the chip.

Date of Award	3 Oct 2012
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Dong SUN (Supervisor)