Microfluidic biosensing using giant magnetoresistance sensors

Abstract

In this thesis, an integrated microfluidic biosensing system using GMR sensors for detecting pathogens according to their velocity in a static fluid is presented. Current carrying conductors are used to displace magnetic microparticles, which are used to label the pathogens, along the detection chamber. Specifically, the magnetic particle (MP) volume increases once a pathogen is attached to its functionalized surface (LMP). If the bare MPs and the LMPs, with the increased non-magnetic volume, are displaced over a certain distance by the same external magnetic field the LMP will travel this distance slower than the bare MP. The velocity of the LMP inside the detection channel is measured and compared to the velocity of the MP inside the reference channel. A GMR sensor is positioned at the inlet of the reference and detection channels respectively and it registers a change in the resistance once the MP and the LMP are introduced. Then they are being accelerated by the magnetic field generated by the current carrying conductors. Once they reach the outlets the GMR sensor positioned there registers a change in the resistance. By knowing the time between the inlet and outlet recorded signals and the traveled distance the velocities of the MP and LMP are calculated. This thesis concentrated on creating an improved measurement system replacing a more expensive bulky device with a cheaper, faster and easier technique. The developed technique uses a PC sound card and MATLAB script to process the signal. Also electronics that will help reducing the effect of thermal fluctuations on the signal by controlling the sensor current flow were developed. Experiments on detecting only a single MP were carried out successfully and a proof of concept of detecting multiple bare MPs and magnetically label E. coli (LMPs) is presented.