An ultrathin sensor spun from gold can be attached directly to the skin without irritation or discomfort. Developed by researchers at the University of Tokyo, the sensor is enabled by Raman spectroscopy and can measure different biomarkers or substances to perform on-body chemical analysis. It can be finely tuned to be extremely sensitive and is robust enough for practical use.
Current wearable technologies can be bulky and costly and are typically limited to functions such as monitoring heart rate. Chemical analysis, highly useful for medical diagnostics, has remained elusive. Prompted by these shortfalls, researchers from the Department of Chemistry at the University of Tokyo sought a way to sense various health conditions and environmental matters in a noninvasive and cost-effective manner.
Surface-enhanced Raman spectroscopy (SERS) can be used to detect the presence of a chemical indirectly by using laser light and a specialized sensor. The gold mesh provides an ideal surface for taking measurements as it does not interfere with the substance being measured. Courtesy of the University of Tokyo.
“A few years ago, I came across a fascinating method for producing robust stretchable electronic components from another research group at the University of Tokyo,” said Limei Liu, a visiting scholar at the time of the study and currently a lecturer at Yangzhou University in China. “These devices are spun from ultrafine threads coated with gold, so can be attached to the skin without issue as gold does not react with or irritate the skin in any way.
“As sensors, they were limited to detecting motion however, and we were looking for something that could sense chemical signatures, biomarkers, and drugs,” Liu continued. “So we built upon this idea and created a noninvasive sensor that exceeded our expectations and inspired us to explore ways to improve its functionality even further.”
The main component of the sensor is the fine gold mesh, as gold is unreactive, meaning that when it encounters a substance the team wishes to measure — for example, a potential disease biomarker present in sweat — it does not chemically alter that substance. But because the gold mesh is so fine, it can provide a surprisingly large surface for the biomarker to bind to. A low-power laser is pointed at the gold mesh, with some of the laser light being absorbed and some reflected.
The gold nanomesh at different magnifications. The individual fibers are much thinner than the thickness of human hair. Courtesy of the University of Tokyo.
Of the light reflected, most has the same energy as the incoming laser light. Some incoming light loses energy to the biomarker or other measurable substance, and the discrepancy in energy between reflected and incident light is unique to the substance in question. A spectrometer uses this unique energy fingerprint so that a user can identify the substance.
“Currently, our sensors need to be finely tuned to detect specific substances, and we wish to push both the sensitivity and specificity even further in future,” said assistant professor Tinghui Xiao. “With this, we think applications like glucose monitoring, ideal for sufferers of diabetes, or even virus detection might be possible.”
“There is also potential for the sensor to work with other methods of chemical analysis besides Raman spectroscopy, such as electrochemical analysis, but all these ideas require a lot more investigation,” said professor Keisuke Goda.
Goda believes the recent research could lead to a new generation of low-cost biosensors.
The research was published in Advanced Optical Materials (www.doi.org/10.1002/adom.202200054).