Feasibility study of wearable sweat sodium sensor

Author: Tianchi Zhang

Zhang, Tianchi, 2020 Feasibility study of wearable sweat sodium sensor, Flinders University, College of Science and Engineering

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In this study, a new wearable sweat sensor has been introduced. Unlike traditional medical wearable devices, which detect physical information such as pulse or heart rate by physical or mechanical, this new type of wearable device is a real-time biochemical information collection device that can quantitate the concentration of sodium ions from human sweat. Through quantitative analysis of the content of sodium ions in sweat, to infer the health status of the human body.

In this project, the properties of three different types of electrodes were tested. These three kinds of electrodes are saturated calomel electrode, screen-printed electrode and modified electrode. They can all react with the free ions in the solution and detect the potential released when the ions undergo a redox reaction. But they all have their own characteristics and properties. These three electrodes have been analysed and selected modified electrodes have been selected as the most suitable electrode to use on this new type of wearable device.

Firstly, the three electrodes were subjected to an electrochemical reaction under the same conditions. The electrodes were connected to an AUTOLAB electrochemical workstation. Observing the results of the open circuit potential (OCP), it was found that the modified electrode can specifically react with sodium ions in sodium chloride solution, and only the potential of the sodium ion reduction reaction is detected on the working electrode. And its small size makes it suitable as part of wearable devices.

Secondly, using the relevant knowledge of signal processing, a functional circuit is designed to collect and process the signals received by the electrodes. This circuit contains a voltage buffer circuit, a subtractor differential amplifier circuit and a 4th order low-pass Butterworth filter circuit. After simulating the designed circuits, Altium Designer is used to make a printed circuit board (PCB), and then the components of the circuit board are soldered. After the soldering is completed, it is connected to the electrode for testing.

An assembled device connected by functional circuits, electrodes and LED modules driven by Arduino can form a complete system. It can be used to detect, process and display microampere-level electrochemical signals. This provides feasibility for the detection of the electrochemical properties of substances in human body fluids.

Keywords: Electrodes, Sodium Ions Detection, Signal Processing, Printed Circuit Board Build, Digital Display

Subject: Engineering thesis

Thesis type: Masters
Completed: 2020
School: College of Science and Engineering
Supervisor: Youhong Tang