A new Raman chemical sensor made from noodle-like threads of gold

Researchers created a special ultra-thin sensor, spun from gold, that can be attached directly to the skin without irritation or discomfort. The sensor can measure various biomarkers or substances to perform chemical analyzes on the body. It works using a technique called Raman spectroscopy, in which laser light aimed at the sensor is slightly altered depending on the chemicals currently on the skin. The sensor can be fine-tuned to be extremely sensitive and is robust enough for practical use.

Wearable technology is nothing new. Maybe you or someone you know wears a smartwatch. Many of these can control certain health issues, such as: heartbeat, but currently they cannot measure chemical signatures that could be useful for medical diagnoses. Smartwatches or more specialized medical monitors are also relatively bulky and often quite expensive. In response to such shortcomings, a team consisting of researchers from the Department of Chemistry at the University of Tokyo sought a new way to detect various health problems and environmental issues in a non-invasive and cost-effective way.

“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 researcher at the time of the study and currently a lecturer at Yangzhou University in China. “These devices are spun from ultra-fine threads covered in gold, so can be attached to the skin without any problem, as gold does not react with or irritate the skin in any way. However, as sensors they were limited to detecting movement, and we were looking for something that could detect chemical signatures, biomarkers and drugs, so we built on this idea and created a non-invasive sensor that exceeded our expectations and inspired us to explore ways to further improve its functionality.”

The most important part of the sensor is the fine gold mesh, because gold is non-reactive, meaning that when it comes into contact with a substance the team wants to measure, for example a possible biomarker for disease present in sweat, it substance does not chemically change. But instead, because the gold mesh is so fine, it can provide a surprisingly large surface area for that biomarker to bind to, and this is where the other components of the sensor come in.

Because a low-power laser on the gold mesh, some of the laser light is absorbed and part is reflected. Most of the reflected light has the same energy as the incident light. However, some of the incident light loses energy to the biomarker or other measurable substance, and the difference in energy between reflected and incident light is unique to the substance in question. A sensor called a spectrometer can use this unique energy fingerprint to identify the substance. This method of chemical identification is known as Raman spectroscopy.

“Currently, our sensors need to be fine-tuned to detect specific substances, and we want to increase both sensitivity and specificity even further in the future,” said assistant professor Tinghui Xiao. “With this, we think that applications such as glucose monitoring, which is ideal for diabetic patients, or even virus detection are possible.”

“There is also a possibility that the sensor will work with other methods of chemical analysis in addition to Raman spectroscopy, such as electrochemical analysis, but all these ideas require much more research,” says Professor Keisuke Goda. “In any case, I hope that this research can lead to a new generation of low-cost biosensors that can revolutionize health monitoring and reduce the financial burden of health care.”