Electrochemical Sensing of Environmental and Biological Samples
Creators: name: Nelson, Anna
Publisher: name: My University
Year: 2023
Subjects: subject: Electrochemical Detection
subject: Ion Analysis
subject: Immunoassays
subject: Microfabrication
subject: Traumatic Brain Injury
subject: Chemical Engineering
subject: FOS: Chemical engineering
subject: Engineering

description: Recent advancements in the sensor manufacturing industry have facilitated the development of rapid, inexpensive, and user-friendly sensors for end-point monitoring of different environmental (e.g., water) and biological (e.g., urine, blood) samples. However, developing portable, simple and long-term sensors with minimal maintenance still remains a challenge as sensors are often reliant on the user with bulky instrumentation and thus, quantification of analytes of interest are primarily conducted by sending samples to a local or central laboratory. Recently, electrochemical sensors have shown promise to develop end-point monitoring systems as they are rapid, easily miniaturized, and inexpensive. In this doctoral research, we focus on development of electrochemical sensors for near real-time monitoring of lead ions in water, quantification of chloride ions in urine samples, and assessment of traumatic brain injury (TBI) biomarkers in blood samples. Lead contamination of drinking water from lead infrastructure used in buildings prior to 1986 is difficult to predict and hazardous to human health. Changes in water chemistry and aging infrastructure can result in large scale public health crisis, as evidenced by the 2014 Flint Water Crisis. Presently, heavy metal water testing is reliant on the user to send water samples into a lab with multi-week wait times. We have developed an end-point sensor capable of monitoring drinking water for 15 ppb lead. The sensor captures electrodeposited lead oxide and triggers when the electrodeposit bridges two electrodes in the four-electrode sensor through a diffusion limited process. We were able to re-design the sensor to reduce the detection time by 40%. Ion monitoring in urine also relies on laboratory testing with long turnaround times. Urinary chloride, one of the most prevalent electrolytes in the body, has been an underutilized indicator of hydration, kidney and heart health. By providing near real-time quantification of urinary chloride concentration, laborious 24-hour fluid collection can be mitigated. To this end, we developed a chronopotentiometry sensor capable of rapid chloride quantification in 3 seconds. With a swept current density algorithm, we demonstrate improved sensor range by quantifying 5-200 mM chloride with a single sensor. We also investigate sensor reusability and effect of pH, temperature, conductivity, and additional ions relevant to the urinary parameter space. Finally, we investigate sensing systems for conditions where present diagnostic tools are lacking, such as traumatic brain injury. Mild TBI is notoriously difficult to identify, and often relies on invasive computerized tomography scans. In 2018, the Food and Drug Administration approved glial fibrillary acidic protein (GFAP) and ubiquitin c-terminal hydrolase L1 (UCH-L1) biomarkers that elevate after a TBI. However, quantification of these biomarkers is primarily dominated by optical detection systems that are high throughput but are limited by bulky detection systems. To improve portability, we develop an enzymatic sandwich immunoassay for electrochemical identification of TBI biomarkers. We use high throughput optical methods to develop a working assay and translate this protocol to achieve electrochemical detection. We then demonstrate rapid amperometric sensing can be achieved in under 5 s for both GFAP and UCH-L1 biomarkers. Lastly, we propose a design and fabrication process for developing a credit card sized variable height microfluidic platform that can be used to multiplex TBI biomarkers of interest. Overall, this work presents sensing systems that can be employed at the end-point for rapid, portable monitoring to provide actionable data to identify harmful substances, disease, and injury progression.