Hydrogel-based Graphene Electrochemical Tattoo (GECT) Sensor for Tyrosine Sensing in Sweat

Abstract

Bloodwork is the most common clinical method for assessing physiological health, both for diagnosing illness and for monitoring chronic conditions. In most cases, blood samples are analyzed using complex lab equipment, which often takes a few days for the results. Yet, despite its routine use, blood samples are obtained through invasive methods, raising the question of why such fundamental health related issues should rely on procedures that come with discomfort and limited availability. The rise in alternative sensors that use other biofluids rather than blood for diagnostics was an approach to address this problem. Tears and saliva are popular alternatives; however, they also face specific challenges in terms of continuous monitoring and comfort. Meanwhile, sweat offers continuous access and comfort. Biomarkers in sweat are closely correlated with their levels in blood, enabling reliable results and assessment. One of these biomarkers is tyrosine. Tyrosine is a non-essential amino acid and the principal precursor for the synthesis of catecholamine neurotransmitters, including dopamine (DA), norepinephrine (NE), and epinephrine. These neurotransmitters are critical for a wide range of physiological and cognitive functions, such as mood regulation, attention, stress response and motor control. However, in order to collect and keep the sweat on the sensing area, microfluidics has been proposed. While they perform excellently in delivering the fluid to the sensor, they are often fabricated from materials with form factors far from skin, causing discomfort to the skin. As the sensor’s thickness increases, it requires additional adhesive material to maintain the wearability goal. Hence, there is a need for a better structure for sweat delivery and collection. This thesis presents a stretchable hydrogel-based graphene electrochemical tattoo (GECT) sensor for tyrosine sensing in sweat. The sensor consists of serpentine graphene-based electrodes, which makes the overall structure stretchable, enabling long-term use up to 4 days.