Design of a Flexible, Wearable Interdigitated Capacitive Sensor for Monitoring Biomarkers of Atopic Dermatitis

The emergence of wearable and remote sensing devices in e-health has revolutionized personalized healthcare monitoring, but the field of dermatology has yet to witness significant progress in this area. The diagnosis and monitoring of atopic dermatitis (AD), a common skin disease causing inflammation and rashes, depend on in-person assessment, leading to subjective evaluations and treatment procedures. This work presents a novel interdigitated capacitive sensor, specifically designed to detect biomarkers of AD and to empirically estimate the severity of the condition. The design was proven by finite-element analysis software to detect only biomarkers of AD-dehydration of the outermost skin layer. The IDC sensor has a compact and flexible footprint (sensing area of around 40 mm(2)); it is compatible with a wearable and noninvasive system, and can be used to remotely gather localized data about the condition. To calibrate its measurements, a novel hydration-gradient skin-mimicking phantom was developed, which simulates varying skin hydration conditions on the same substrate. The sensor is compared against a commercial skin hydration device, and its sensitivity is mapped against the arbitrary units (A.U.s) of the commercial device, resulting in a normalized capacitance sensitivity of 13.1 pF/cm(2) per 1 A.U. This novel IDC sensor is the first sensor to accurately measure the permittivity of specific layers of the skin. Its bespoke design is the main enabler of the outermost layer's permittivity to be isolated from the skin. This presents promising prospects for remote patient care, enabling accurate diagnosis, treatment monitoring, and personalized interventions for AD.