Measuring Electrodermal Activity Underwater using Graphene Electronic Tattoos

Oxygen, while essential for human function, can be harmful in the context of underwater diving. Divers, to stay safe underwater, need to breathe pure, pressurized oxygen known as hyperbaric oxygen; however, breathing too much of this hyperbaric oxygen at certain depths and pressures risks the development of Central Nervous System Oxygen Toxicity (CNS-OT). CNS-OT can lead to sympathetic overstimulation and cause seizures, which are due to abnormal electrical activity in the brain. Electrodermal Activity (EDA) is a quantitative index of sympathetic nervous system activity measured through changes in skin conductance, which vary according to sweat levels caused by emotional arousal or stress. A significant surge in EDA amplitude is a precursor to epileptic seizures and used as an early indicator for CNS-OT risk. Developing a method to identify the onset of CNS-OT risk underwater means introducing a safety monitoring approach previously unavailable in diving. Currently, commercial EDA devices, while effective, lack the flexibility and wearability of GETs and are not waterproof. We propose a graphene electronic tattoo (GET) capable of EDA data processing while immersed in saltwater conditions through a four-part experimental process. First, we established a control group by measuring bioimpedance with uncovered GETs in air, DI water, and saltwater. Next, we found the best waterproofing sealant by comparing the baseline measurements of bare GETs to GETs covered individually by three sealants. After finding that Nexcare Skincrack Care (NCC) produced the clearest bioimpedance readings in each condition, we used this sealant for electrocardiogram measurements in the same fluid conditions to validate our GETs capacity for underwater measurements. Finally, we took EDA measurements using a Neulog device by simulating three emotional states: meditative, focused, and stressed through meditation, boring videos, and horror videos. We established an EDA baseline using the commercial electrodes in each emotional state in air then proceeded to measure EDA with our GET sealed by NCC in the conditions of air, DI, and saltwater. The maximum stimulated EDA change obtained by our graphene electrodes in saltwater is 0.217 μS with a response time of 4 seconds, which is comparable to the commercial electrodes in air with a similar response time. As a result, we find that the combination of NCC and a GET enabled successful EDA monitoring in seawater conditions, advancing GETs in underwater medicine.