Dec 4, 2018
Jolley Hall, Room 309
"Biosensing by 'Growing' Antennas and Error-correcting Codes"
Adviser: Shantanu Chakrabartty
Food-borne disease outbreaks not only cause numerous fatalities every year but also contribute to significant economic losses. While end-to-end supply chain monitoring can be one of the keys to preventing these outbreaks, screening every food product in the supply chain is not feasible considering the sheer volume and prohibitive test costs. Fortunately, two converging economic trends promise to make this end-to-end supply chain monitoring possible. The first trend is that passive radio-frequency identification (RFID) tags and quick response (QR) codes are now widely accepted for food packaging. The second trend is that smartphones are now equipped with the capability to interrogate RFID tags or to decode QR codes. Together, they have opened up the possibility of monitoring food quality by endowing these tags and error-correcting codes with the capability to detect pathogenic contaminants. This dissertation investigates a biosensing paradigm of ``growing'' transducer structures, such as RFID tags and QR codes, which is triggered only when analytes of interest are present in the sample. This transducer growth or self-assembly process relies on a silver enhancement technique through which silver ions reduce into metallic form in the presence of a target analyte, which in turn leads to changes in electrical or optical properties. By exploiting this, we first demonstrate two remote biosensor platforms, a RFID tag-based biosensor and a QR code-based biosensor, respectively. For the RFID-based biosensor, a chain of silver-shelled particles is assembled during the analyte detection process, which directly modulates the antenna's effective impedance, and hence leads to an improvement in the tag's reflection efficiency. For the QR code-based biosensor, the operating principle relies on the optical absorption changes resulting from silver enhancement. The target detection process assembles an invalid code-word into a valid QR code. This self-assembly sensing approach should produce few false positives since it is a process which transits from a high entropy state (disassembled transducer) to a low entropy state (assembled transducer). While there can be numerous states of a disassembled transducer structure, there are only a few configurations representing the assembled transducer state. Given that there are no active power sources on the RFID tag or the QR code, it is challenging for the proposed biosensors to perform sample acquisition and pre-processing since they are envisioned to be embedded inside food packages eventually. Paper-based microfluidics have been explored and integrated on the biosensors to provide a self-powered approach for reagent sampling and processing. One use case is to trigger target detection remotely by an end consumer. Thermal absorption properties of graphite have been exploited to drive the process of analyte sampling in paper-based biosensors.