Resumen de Optofluidic device for cytometric measurements and study of inertial focusing conditions in asymmetric serpentines
In this thesis we study the cytometric capabilities of a microfluidic device and the focusing behavior of particles under inertial focusing conditions. Since its gradual implementation throughout the 80's, microfluidics has demonstrated unmatched capabilities to perform cytometric measurements by means of the join application of different physical processes in a single microfluidic device. Additionally, the implementation of microfluidics to conventional industrial processes, chemical analyses,... is commonly attributed with inexpensive approaches. It is therefore a good candidate for low-cost solutions in the fields of engineering, chemical and medical sciences.
This work presents an optofluidic device capable to detect and classify individual cells by means of an hydrodynamical focusing scheme and two interrogation regions. The device captures the luminous signal from fluorescent-labeled cells through optical fibers inserted in the device. In order to illuminate the cells, pump light is injected to the device with optical fibers which are carefully aligned with the microfluidic channel where cells flow through. The use of two interrogation regions permits a correlation analysis which translates in higher signal-to-noise ratios from the detection of cells without the need of noise reduction devices. Our device is able to classify the detected cells according to their luminous signature in sample ratios prepared in the laboratory. The intended use of this device is the detection of circulating tumor cells in blood samples.
This thesis also presents results in the field of inertial microfluidics and, more specifically, in the field of inertial focusing for rigid spherical particles in serpentine channels. This is a very interesting effect since the precise focusing of particles/cells is a long pursued topic in the field of flow cytometry, where the positioning of cells is a determinant factor in the validation of the outcome in any cytometric measurement. Inertial focusing allows the precise positioning of cells along equilibrium trajectories when they are flowing within a microfluidic channel under inertial focusing conditions, that is, when the flow rate is sufficiently high. The process of particle focusing and alignment is, on the other hand, a completely passive effect; no external force or agent has to be applied in order for the cells to focus, which greatly reduces the complexity of the measurement process and improves its repeatability. The use of a curved geometry (a serpentine) causes the emergence of transverse flows which, working in conjunction with the inertial migration of the particles, improves their focusing efficiency. Our results are presented along simulations performed under the same experimental conditions to visualize the behavior of the flow and the particles when these are completely focused in this somewhat exotic regime. Further results reveal the relationship between the slight variations of the flow conditions around the particles and their focusing degree and how they tend to translate along vortices' centerlines in curved channels. The purpose of this work is to provide with additional knowledge about the behavior of particles in these conditions so new tools can be used and inertial focusing mechanisms can be more efficiently utilized in the field of flow cytometry.
