Investigation of an integrated flow-cytometry chip using hydro-dynamic focusing and cell sorting

Abstract

Recent years have seen a growing focus in the field of microfluidic technology as a powerful tool in medical diagnostic research. Micro-flow cytometers, micro mixers, cell sorters and cell analysers are only a few examples. Among these examples, cell manipulation has been widely investigated using various methods, like magnetic, electrical, mechanical, and hydrodynamics. In past, quite a few methods and techniques have been used to achieve a tight focused stream of cells and it was observed that contrary to the popular belief, inertia does have a contribution factor in microfluidic phenomena. This thesis utilizes hydro-dynamic focusing as the cell manipulation technique. Out of all the focusing techniques; hydro-dynamic focusing, in particular, was favoured as it requires no external forces resulting in simplified design. Focusing particles in a tight stream is a pre-requisite before counting, detecting and sorting them. Lab-on-a-Chip (LOC) is a device that integrates multiple laboratory functions on a single miniaturized chip. There are three steps to LOC for medical diagnostics; cell focusing, cell sorting and cell counting/analysis. It is a novel technology and still being developed. While researchers have developed and tested their designs, the optimum design is yet to be attained. This thesis presents our own design of the micro-channel to simulate cell focusing using elasto-inertial techniques. Successful simulation were run to validate our design by conforming to a focus cell stream to be detected. Sheathless inertial focusing of particles in microchannels is a great step in lab-ona- chip applications. This technique can provide a high throughput of cell focusing based on the finely tuned balance of wall interaction force, shear gradient force and the drag of secondary flow. We present the three dimensional numerical simulation of the effect of inertial migration in focusing of biological cells in a viscous flow medium at a high throughput. The inertial focusing of the particles is theorized and simulated by undertaking parametric study of the size of the particles, rate of flow, and the dimensions of the microchannel. Since cells focusing is the key point for the correct operation of a flow cytometer, several efforts have been made in order to reproducing it in a proper way on a microchip. In most cases, the traditional hydrodynamic focusing mechanism employing viii sheath fluid has been translated to the micro-scale. The main drawback in the approaches proposed till now, is that multiple inlets are needed. This brings to a high complexity if parallelization has to be introduced into the device. It is important to take in consideration that lab-on-chip technology introduced a breaking point in the design of bio-technological instrumentations, since there is not anymore interest in expensive bench-top instruments able to perform multiple analysis, but in small, cheap and disposable devices ad hoc for a single purpose. For this reason, in this work, it was necessary to define the cellular target, considering that since the optimization of the designed geometry mainly depends on the cell dimension. In particular neutrophil count was chosen as a diagnostic test. Low neutrophil count can be a result of radiation, chemotherapy, or bone marrow transplant, its recovery means that new blood cells are starting to grow and mature. High neutrophil count is an indication of acute bacterial infection, which elevates the WBC count. This paper provides an efficient design of parameters for focusing WBC particles in a microchannel and has application in multiple microfluidic devices.