Ultrasensitive Magnetometry for the Quantitation of Magnetic Assays

The accessibility of reliable diagnostic, play a vital role in health care costs, decisions, treatment and possible survival rates. Point-of-Care (POC) diagnostic is currently the most accessible form of medical diagnostic because it is affordable, sensitive, specific, user-friendly, rapid/robust, equipment-free/minimal, and distributable to those in need. A familiar POC device is a pregnancy test strip. It can be purchased at a local store for less than the cost of a meal, and the consumer can perform the test and interpret the results without training or prior knowledge. Unfortunately, the low sensitivity of the test strips limits its applications to health issues that produce copious amounts of diagnostic markers.

In this dissertation, we investigate a transformative biosensor based on the principles of magnetic induction that can enhance the sensitivity of the test strip. The radical design was modeled, simulated, constructed and evaluated to demonstrate feasibility. The knowledge gained from the first prototype lead to a couple of innovations in design and fabrication. The second generation sensor is approximately the size of a dime and costs several dollars in parts. The sensitivity is comparable to the state-of-the-art commercial system which costs over $50,000.

The third generation of the sensor, named femtoMag, further increases the sensitivity 100 folds and can detect magnetic moments as low as $10-10$ emu or 20000 number of magnetic nanotags. The biosensor platform was demonstrated by reading a pregnancy test strip where the target labels are replaced with magnetic nanotags. The femtoMag was able to detect as little as 0.01 ng/mL of hCG, the pregnancy hormone.