Spider silk-based fibre optic sensor gets the measure of glucose

The new light-based sensor developed by a team in Taiwan could eventually find use in measuring blood sugar and other biochemical analytes.

“Glucose sensors are crucial to people with diabetes, but these devices tend to be invasive, uncomfortable and not cost-efficient,” said research team leader Cheng-Yang Liu from National Yang Ming Chiao Tung University. “With spider silk attracting attention for its superior optomechanical properties, we wanted to explore using this biocompatible material to optically detect various sugar concentrations in real-time.”

Liu and colleagues from Taiwan Instrument Research Institute and Taipei Medical University describe their new sensor in Biomedical Optics Express. They show that it can be used to determine concentrations of fructose, sucrose and glucose sugars based on changes in a solution’s refractive index. Spider silk is said to be suited for this application because it can transmit light like an optical fibre and is very strong and elastic.

“Our new spider silk-based fibre optic sugar sensor is practical, compact, biocompatible, cost-effective and highly sensitive,” Liu said in a statement. “With further development, it could lead to better at-home medical monitoring devices and point-of-care diagnostic and testing devices.”

To make the sensor, the researchers harvested dragline spider silk from Nephila pilipes, a species of golden orb-web spider. They enveloped the silk with a biocompatible photocurable resin and cured it to form a smooth protective surface. This created an optical fibre structure that was 100 microns in diameter, with the spider silk acting as the core and the resin as the cladding. They then added a biocompatible nanolayer of gold to enhance the fibre’s sensing abilities.

This process formed a thread-like structure with two ends. To use the fibre to take measurements, the researchers immersed one end in a liquid sample and connected the other end to a light source and a spectrometer, which allowed the researchers to detect the refractive index of the solution and use it to determine the type of sugar and its concentration.

“The spider silk-based sugar sensor is reusable, cost-effective, easy to use and offers real-time detection,” said Liu. “Moreover, because it is compact it could allow access to hard-to-reach areas such as the brain and heart. With further development, it is also hoped that this silk-based fibre optic sugar sensor could be used in implantable medical devices and treatment strategies in biomedical applications.”

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To test the repeatability and stability of the sensor, the researchers used it to measure solutions with unknown concentrations of fructose, sucrose or glucose sugars at room temperature. The measurements were each repeated 10 times at five-minute intervals.

To quantitatively determine the performance of the silk-based fibre optic sensor, the researchers compared the light intensity spectra produced by the sensor with refractive index measurements acquired with a commercial refractometer. The sensor was able to identify the type of sugar in the solution and provide a readout of the concentration.

Before the sensor can be used for real-time measurements it will be necessary to improve its accuracy and enhance its stability under environmental changes so that it can be used for longer periods of time.

The researchers are also working on software that would allow the sensor to be used with mobile devices for point-of-care readings. They also want to extend the sensor’s functionality so that it could be used to measure different biochemical components in human blood such as lactose and fat.