Smart, Wearable and Power-Controlled Mixed-Signal Platform for Screening and Follow-Up of Cystic Fibrosis Based on Real-Time Chloride Concentration Evaluation in Sweat
Cystic fibrosis (CF) is a severe genetic disorder caused by mutations in the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene. It mainly affects the lungs and digestive system. Diagnosis relies on the sweat chloride test, which measures chloride ion concentration in sweat. Although reliable, it requires adequate sweat collection, trained staff, a laboratory setup, and pilocarpine-induced iontophoresis, making accurate interpretation critical. With the advent of CFTR modulators and administration of the drugs that correct the defective protein, frequent monitoring of sweat chloride has become vital for evaluating therapy. However, traditional methods are costly, time-intensive, and inconvenient.
To address these challenges, researchers have developed a wearable sweat sensor system designed for continuous, at-home monitoring of CF. The device is integrated into a flexible armband and is optimized for low power consumption, comfort, and portability. It combines replaceable, biocompatible potentiometric electrodes, onboard data analysis capabilities, Bluetooth Low Energy (BLE) communication, and a microcontroller-based control system to support real-time diagnostics. The system is capable of acquiring, processing, and wirelessly transmitting test results to healthcare providers via Fast Healthcare Interoperability Resources (FHIR)-compliant servers, supporting remote care and long-term treatment evaluation.
The hardware comprises a flexible printed circuit board (FlexPCB) with compact electronics measuring just 49.4 × 39.5 mm, enabling the device to be comfortably worn even on small children or infants. The sensing mechanism includes working and reference electrodes fabricated on a plastic substrate, with the reference electrode treated using silver oxide. Chloride ion concentration is detected using an Open Circuit Potential (OCP) sensing block and a precision signal-processing chain featuring a fourth-order Sallen-Key low-pass filter with a cut-off at 195.6 Hz. The microcontroller (NINA-B306 based on nRF52840) operates at 64 MHz and is supported by 1 MB flash and 256 kB RAM. Signal conditioning is achieved using low-bias current op-amps (MAX44242, MAX4477), and a 14-bit DAC (LTC2611) calibrates voltage offsets to maximize analog-to-digital conversion range.
The firmware, termed “Sweat Test Controller,” automates data acquisition and analysis. Activation can be triggered via battery insertion, the touch sensor, and the real-time clock (RTC). The firmware supports various modes such as calibration using sodium chloride solutions, real-time testing, and output offset adjustment. The device’s power management is highly optimized. During active operation, components like the op-amps and BLE module draw about 1.78 mA on average, while standby mode consumes only ~100 µA. A 3.7 V, 200 mAh coin-cell battery provides power regulated to 3.3 V, offering a battery life of approximately 82 days based on an average power draw of 350 µW. After maintaining non-pathological readings, the device enters a system-off mode, concluding the monitoring cycle.
This wearable sweat sensor offers a compact, reliable, and user-friendly platform for real-time, remote CF monitoring. Future enhancements may include a micro-heater to stimulate sweat by warming the skin to 25 °C for 10 minutes, consuming just 20 mW, further extending its functionality for on-demand testing without compromising energy efficiency.