Wearable Electrochemical Microneedle Sensors Based on the Graphene-Silver-Chitosan Nanocomposite for Real-Time Continuous Monitoring of the Depression Biomarker Serotonin

Wearable microneedle-based electrochemical sensor technologies are promptly growing due to their unique capabilities, such as minimally invasive, painless, real-time, continuous monitoring, etc. Strong disruptions or imbalances of neurotransmitter systems are associated with many chronic diseases and mental disorders, including Parkinson's, depression, anxiety, memory loss, significant changes in weight, and chronic physical or emotional stress. The captivating advantages of the wearable microneedle-based sensor enable continuous monitoring of various biomarkers and pharmaceutical drugs in interstitial fluid (ISF). In this present work, we have developed a sensor for continuous monitoring of the biologically important neurotransmitter Serotonin (5-hydroxytryptamine, 5-HT) through a microneedle patch. The new microneedle sensor array relies on Ag/rGO-modified carbon paste microneedle electrodes for square wave voltammetry and amperometry detection of the 5-HT target. Such real-time orthogonal sensing offers distinct, unique information and the desired analytical performance. The surfaces of the working electrodes have been characterized with electroanalytical and surface morphological techniques. The developed sensor was able to detect 5-HT target from phosphate-buffered saline buffer within linear ranges of 3–21 and 6–60 μM (both short and long ranges) with well-defined linearity. The continuous monitoring and biofouling studies of the microneedle sensor were demonstrated in artificial ISF containing bovine serum albumin by using chronoamperometry. The sensor exhibited linearity in the range of 13.5–95 μM. The long-term monitoring capability of the sensor was demonstrated in an artificial ISF medium. The specificity of the sensor was exhibited in the presence of potentially interfering substances. The excellent performance shown in the skin-mimicking model proved that the microneedle sensor platform holds considerable promise for real-time detection of the important neurotransmitter 5-HT in the ISF.