Electrochemical Sensing of Cytokines Utilizing Carbon Nanotube Fiber-Based Electrodes

Aptamer based biosensors are a promising tool for further understanding mechanisms underlying various systems in the body at a molecular level. Aptamers allow for indirect electrochemical sensing of chemicals and biomolecules. As a specific target molecule binds to the aptamer, there is a conformation change. Scientists have taken advantage of this conformation change and designed aptamers that bring the charged free end closer to the surface of an electrode, sensing an electrochemical change in response to the chemical concentration. However, the binding of aptamers to the surface of metal electrodes has shown to be very fragile, making the lifespan of such biosensors limited. For <i>in vivo</i> and even future clinical applications, the devices need to be stable both in and out of solution for long periods of time. We propose using carbon nanotube fibers (CNTf) to improve the adhesion of aptamers to the surface of electrodes. CNTfs have great chemical stability, electrical properties, and high effective surface area making them ideal candidates for the substrate of the devices. The chemical bond between carbon and the aptamers is more stable than that with gold, a conventional biocompatible electrode material, allowing for a more stable device. To test this device design, we use aptamers that selectively bind to IL-6. The IL-6 aptamers are immobilized and attached to the CNTf using electrochemical conjugations. After successful attachment has been validated, the sensitivity of the device and limit of detection are evaluated and optimized. After optimization, the response time, lifetime, and biofouling response are analyzed. This is initially done in phosphate buffered saline (PBS) solution, but further testing in animal models is planned. The functionalized device can be used to decode immune status in blood using pro- and anti-inflammatory cytokines at physiologically relevant concentrations. This opens the door to being able to both monitor and intervene in the immune system using bioelectronic interfaces, with the CNTf sensor recording real-time immune system status and a future electrical interface with the nervous system modulating the immune system based on data from the sensor, a systems-level approach which has not been done before.