Tuning SLOCK toward Chronic Disease Diagnostics and Management: Label-free Sweat Interleukin-31 Detection

Abstract

SLOCK (sensor for circadian clock) is an electrochemical sweatbased biosensing platform designed for the diagnosis and management of circadian abnormalities. Previously, the SLOCK platform was designed to detect adrenal steroids, cortisol, and DHEA for tracking the circadian rhythm. This work aims at tuning this SLOCK platform toward the detection of the cytokine, interleukin-31, for building a noninvasive, chronic disease diagnostics and management platform. This research provides a detailed characterization of the sensing surface and immunochemistry. The results show that SLOCK has good sensitivity to IL-31 concentrations in synthetic and human sweat. The limit of detection is 50 and 100 pg/mL for synthetic and human sweat, respectively. The dynamic range of the system is 50−1000 pg/mL, which encompasses the physiological ranges of 150−620 pg/mL. This is the first demonstration of sweat-based, label-free, electrochemical detection of IL-31. In addition to this, the data show good correlation (R 2 > 0.95) for the signal sensitivity to biomarker concentration. Finally, cross-reactivity studies highlight the specificity of SLOCK even in the presence of highly cross-reactive species. Thus, this novel SLOCK biosensor can be successfully used to track IL-31 in a sensitive and noninvasive manner and could be used to identify chronic pathophysiologies present in the body.

Passive Sweat-Based Pruritic Cytokine Detection and Monitoring System

“…This affinity-based sensing chemistry was previously characterized using FTIR, SPR, and impedance analysis. 19,22 This confirmed the successful functionalization of immunochemistry on the electrode surface. Nonfaradaic electrochemical impedance spectroscopy (EIS) is used as the detection modality in this work.…”

“…Previously, the SLOCK platform (Sensor for circadian clock) was characterized for its sensitivity to IL-31 in sweat. 22 The results from this work highlight the ability of the platform to detect IL-31 over the dynamic range of 50-1000 pg ml −1 . It also shows high specificity to IL-31 even in the presence of similarly structured molecules like IL-6.…”

“…Additional details about the substrate and fabrication has already been provided in the previously published works. 21,22,27 Experimental design for single frequency EIS.-Single frequency EIS was performed using a Gamry Reference 6000 potentiostat (Gamry Instruments, PA, USA). The EIS experiments involved a 10 mv sinusoidal input and the impedance was recorded as the output.…”

“…The temporal analysis was performed at 15 hz, where maximum capacitive behavior of the system was observed. 22 Simulated profiles were created by dosing with spiked synthetic and human sweat. These concentrations are presented as ratio change from baseline, which is blank synthetic sweat or unspiked human sweat.…”

Wearable electrochemical biosensors to measure biomarkers with complex blood-to-sweat partition such as proteins and hormones

“…The enlargement of the scope analysis of the SLOCK platform for cytokines present at eccrine secretion was made recently by Prof Prasad's lab researchers. An LDR of 50–1000 pg·mL −1 for IL-31 [ 108 ] suggests the real possibility of ILs monitoring into the sweat by WEB-SPEs. The outstanding device called EnLiSense's skin-SWEATSENSER is capable of sensing four different inflammatory cytokines (i.e., IL-6, IL-8, IL-10, TNF-α) from passive eccrine sweat in a continuous real-time manner (Fig.…”