Bioimpedance & dielectrophoresis instrumentation equipments for living cells manipulation and monitoring

Abstract

Since the first microfluidic device was developed in the early 1950s, when the basics for today’s inkjet technology were set, thousands of publications have appeared related to the topic. The increasing interest on these technologies is caused by its ability to be scaled and its rapid development, which allows manipulating and detecting small quantities of analites even at the cellular scale. The integration of microfluidic technologies with specific sensors and actuators at minute scales in order to achieve a set of automated laboratory operations and perform a particular solution for a specific application, generally on the life sciences and chemistry fields, was defined as Lab-on-a-chip (LoC). LoC devices have the potential to become a powerful technology for some fields, such as health, food security or environmental control. Their low cost and portability make them also suitable to improve medical diagnosis and research in developing countries. Moreover, these systems permit also to explore new methods for manipulation and characterization of cells by means of electrical cell properties, by using techniques such as dielectrophoresis (DEP) or impedance spectroscopy (IS). In fact, the dielectrophoretic force allows manipulating cells, taking advantage of their electrical properties, by applying an electric field. Likewise, impedance allows measuring electrical properties of materials and, used wisely, inform about characteristics such as presence, composition or size of cells or other biological materials.

This work aims, in its final stage, to exploit the combined potential of both techniques, DEP and IS, in a compact system for bioanalytical bench-top applications. The creation of the complete device has been a long procedure alternating theoretical calculations and experimental tests. It has included different steps such as the design of the need electronic equipment stages, the study of different microfluidic designs, an accurate bacteria concentration and manipulation protocol definition, and the study of the viability of the bacteria populations recovered with our device. These studies have made possible to finally obtain an automated bacteria concentrator for microbiology, food, water and environmental control applications while performing impedance cell analysis to monitor bacteria accumulation during the process. The system has been adjusted and proved for the real case of Escherichia Coli (E. coli) concentration and analysis. E. coli presents pathogenic variants that cause morbidity and mortality worldwide being therefore a topic of interest. E. coli is one of the main antimicrobials resistant pathogens in healthcare-associated infections reported to the National Healthcare Safety Network, being the primary cause of widespread pathologies such as significant diarrheal and extra-intestinal diseases or urinary tract infections. Furthermore, E. coli can be found as a bacterial food contamination and causes avian coli-bacillosis, one of the major bacterial diseases in the poultry industry and the most common avian disease communicable to humans. Currently, bacterium presence detection involve long time culture processes only to obtain a valid sample which could be properly detected. DEP concentration is a strong selective manipulation method which allows reducing sample preparation time. Moreover, by taking profit of IS, E. coli could be rapidly detected in the same equipment. For that reason, it is thought the proposed devices will be a useful tool for some current microbiology laboratories.

Hence the mainly aims of the present thesis are: (I) to prove the feasibility of custom DEP generator for controlling bacteria and find the best signal to accomplish this, (II) to look for the best microfluidic chip option for bacteria preconcentration purposes on bioanalytical applications, (III) to test the feasibility of a custom IS device and (IV) to use the previous studies to design a complete electronic equipment, taken profit of combination of both techniques to have an autonomous system (V) To demonstrate the proof of concept of the full device with the real case of E. coli concentration.

El objetivo de esta tesis es el diseño de una instrumentación capaz de manipular y caracterizar células, a fin de realizar análisis más exhaustivos de elementos biológicos y acelerar procesos de detección de patógenos para aplicaciones de diagnóstico o de control de calidad de alimentos. El dispositivo se centra en dos tipos de técnicas eléctricas para la manipulación y detección de células: La dielectroforesis (DEP) y la medición de la bioimpedancia.

La DEP permite manipular material biológico por medio de campos eléctricos, aprovechando las propiedades eléctricas de la célula y el medio en que se encuentra. La manipulación es por tanto ajustable, mediante el control de estas propiedades, así como a través de la geometría de los electrodos usados, la frecuencia y el módulo de la tensión aplicada. Por otro lado, la IS permite caracterizar material biológico mediante su comportamiento eléctrico en frecuencia. La medida se realiza a través de la aplicación de una corriente alterna controlada y la monitorización del efecto sobre el tejido mediante potencial eléctrico. Los dispositivos de IS son fácilmente integrables con técnicas dielectroforéticas de manipulación, fusionando manipulación con detección.

En esta tesis, la combinación de estas técnicas permite la concentración de pequeños patógenos en grandes volúmenes de muestras y su posterior detección. Para ello, se crean diversos módulos de instrumentación electrónica. Algunos, están dedicados a generar señales alternas desfasadas a frecuencias óptimas para la manipulación de patógenos (módulo DEP). Otros, combinan módulos de generación, lectura y tratamiento digital, para la monitorización del comportamiento eléctrico de células (IS). Los módulos diseñados son validados en un entorno real controlado para concentrar y detectar la bacteria Escherichia Coli en grandes volúmenes de agua. Como resultado, se obtiene una electrónica modular válida, autónoma, portátil y de bajo coste, capaz de disminuir tiempos de preparación y detección de muestras en laboratorio.