Power/Performance Bits: Jan. 10

Muscle-tracking clothing
Researchers from the University of Utah and Gyeongsang National University developed a low-cost bioelectrical sensor that can be integrated into clothing.

The sensor measures electromyography (EMG) signals that are generated in muscles when they contract. EMG signals are useful for studying muscle fatigue and recovery and could potentially be used to inform diagnosis and treatment of neuromuscular diseases.

“The signal we measure is a voltage over a time,” said Huanan Zhang, an assistant professor of chemical engineering at University of Utah. “Every time your finger moves, the potential of the body, of the muscle, changes. So, we are able to detect that difference in potential.”

By embedding the sensor in clothing, it can both be more comfortable and have better contact with skin. Initially, the researchers printed silver paste directly onto fabric. However, prolonged exposure can lead to skin irritation.

To solve the issue, the team deposited a layer of gold nanoparticles on top of the silver. The gold completely encapsulated the silver particles, preventing them from touching the skin. The detector that was both conductive and nonirritating to the skin and used a small enough amount of gold and silver to remain inexpensive.

The sensor was tested by placing it on the bicep and fingers and monitoring the detected signal as those muscles progressed through various exercises. It also withstood washing: they retested sensor performance after multiple washings and found its performance remained high.

“This work not only designs a wearable device, which has the convenience factor, but it also has great performance and is biocompatible,” said Zhang.

Candy health sensors
Researchers from Korea University propose using soft candies as cheap, disposable sensors for single-use diagnostic testing to monitor ovulation or kidney health.

The researchers said that while disposable test strips for single-use diagnostic testing are becoming common, they can be expensive and generate a large amount of waste. Instead, they used electrically-conductive Tootsie Rolls as an electrode to detect salt and electrolyte levels in saliva. Saliva would be collected by licking the candy sensor.

To make the prototype sensor, the Tootsie Roll was flattened and pressed with a crosshatch pattern to hold the saliva sample. Then, they inserted two thin, reusable aluminum tubes, which acted as electrical contacts, connecting the candy electrode into a circuit with a current source and an output voltage detector. In preliminary tests, the device could measure salt levels that were physiologically relevant for health monitoring in a salt-water solution and artificial saliva.

When covered in diluted artificial saliva, the sensor could reliably measure a change in voltage low enough to detect the 10-30% drop in salts that occurs when a person ovulates. While the maximum salt content in the artificial saliva samples was similar to that of a healthy adult, the researchers used calculations to estimate that conductivities three times higher, which signal a problem with the kidneys, would be within the measurable range of the device.

The sensor still needs to be tested with real human samples, but the researchers hope that using soft candy as electrodes could lead to low-waste, inexpensive electrochemical sensors and circuits in the future.