UC San Diego

Facing unprecedented population-ageing, noncommunicable diseases (NCDs) have become the primary risk of death. According to the World Health Organization (WHO), more than 80% of deaths are caused by NCDs in countries where at least 20% of the population is over 60 years old. Inevitably, the growing impact of NCDs necessitates changes to the contemporary healthcare system that was designed many decades ago. One of the key factors of NCD management is to transition diagnostics from centralized laboratories closer to the patient in point-of-care (PoC) settings. PoC settings provide high effectiveness, low cost, easy access, and fast turnaround, PoC diagnostics exhibits timely detection and treatment monitoring of cancers where early detection has a huge impact on the treatment outcome and survival rate while simultaneously reducing the economic burden. Optical-based instrumentation is still the workhorse in clinical diagnostics, however, such instrumentation requires complex optics, lasers, and photodetectors making it hard to translate to the PoC. To address cancerous detection for NCD control, a magnetic biosensor provides an alternative platform for PoC-friendly settings like rapid turnaround time and miniaturization without the loss of sensitivity.

In this dissertation, magneto-biosensing techniques for cellular and molecular assays are presented. We developed a magnetic flow cytometer (MFC) using a giant magnetoresistive (GMR) biosensor and matched filtering to perform aptamer-based cellular assays. This work established the strategy of system design for dynamic throughputs and improved the accuracy to 95%. We extended the results to detect pancreatic cancer cells with over-expressed epidermal growth factor receptor (EGFR). The magnetic measurements were highly correlated with optical signal, revealing the future clinical potential. In terms of molecular detection, we implemented time-domain magnetorelaxometry (MRX) on GMR devices. An ultrafast electromagnet was designed to minimize the deadzone and allow the investigation of Néel relaxation. The effect of the applied magnetic field and magnetization time were explored to understand the relaxation process. The results showed excellent agreement with the empirical trend describing the relaxation based on natural-log behavior. We used these findings to optimize the system and perform a proof-of-principle magnetic immunoassay, the first time that GMR sensors have been reported for an MRX bioassay.