| dc.description.abstract | Continuous real-time surveillance of biological markers can have significant implications on disease prognosis. To date, most commercially available continuous monitoring health systems are physical sensors due to the ease of use and non-invasive detection systems. On the other hand, continuous glucose monitoring (CGM) systems that tracks ISF glucose levels are the only commercially available wearable biochemical sensors. These wearable CGM systems significantly improve patients’ diabetes management and prognosis, illustrating that biochemical wearable sensor to monitor other biomarkers, such as lactate, can be highly beneficial. As a product of anaerobic metabolism, blood lactate levels are often used to evaluate health conditions such as endurance capabilities, severe infection, and respiratory failure management of critically ill patients. There are major development and commercialization of blood lactate monitoring systems, but commercially available sensors are hand-held devices that require frequent extraction of blood samples. Thus, there is dire need for a wearable lactate sensor. This thesis presents and investigates the development of wearable carbon nanotube (CNT) based lactate biosensors.
A stable enzyme matrix is one of the most important components of biosensors. Covalently linking the enzyme with glutaraldehyde is a common approach but can decrease the enzyme activity. The non-covalent technique relies on using a semi-permeable membrane, such as Nafion, to stabilize the immobilized enzymes. Nafion has been widely used for enzyme immobilization for its high stability and ionic conductivity. Our results demonstrated that the non-covalent approach retained higher enzymatic activity for the glucose sensor compared to the covalent cross-linking technique. Through electrochemical impedance spectroscopy, the 1% Nafion membrane was shown to be stable on for 24 hours.
The incorporation of carbon nanotubes in biotransducers have improved sensors’ sensitivity due to their high aspect ratio and ballistic electrical conduction due to the sp2 hybridized carbon. However, many CNT sensor designs fail to take full advantage of the CNTs’ high surface area by placing the CNTs between the enzymes and electrode, squandering a significant portion of conductive surface area that can be used to transmit signals. The multiwalled carbon nanotube (MWNT) used was grown through chemical vapor deposition and had an average diameter and length of 8.28 nm and 150 µm, respectively. Unlike commercially available MWNTs that require purification in acidic solution which consequently introduced defects, the MWNT forest was pristine and preserved the electrical properties. The MWNT was coated with chitosan (CHIT) to improve solubility and integrated in the enzyme matrix to create a porous 3D CNT-enzyme matrix. Our results show that the CNT integrated enzyme matrix slightly increased in sensitivity. The fabrication of a conductive and hydrophilic matrix depends on the optimal ratio of CNT to CHIT and CNT-CHIT to LOx.
Lastly, we developed a wearable microneedle platform that consists of a hollow microneedle array, polydimethylsiloxane (PDMS) chamber, and sensor strip. The platform utilizes a pressure-driven convection technique by designing a pumping mechanism on the top of the PDMS chamber. The platform successfully extracted up to 500 µL of solution with a viscosity comparable to blood.
This study investigates the development of biochemical sensors for continuous monitoring. Our 3D CNT-enzymatic matrix offers new insights and approaches to produce stable and sensitive sensors towards the actualization of wearable biochemical sensors. | en |
