Fiber-optic sensor from spider silk points to new point-of-care diagnostics

10 Aug 2022

NYCU Taiwan project uses material's light-guiding properties to detect sugar concentrations.

The prospect of exploiting spider silk's combination of optical and mechanical properties has been an attractive proposition to designers for some time.

Back in 2008 a project at Tufts University investigated whether a silk worm's cocoon could be turned into fully functioning optical components that were biodegradable and biocompatible. In 2016 a UK team used silk from the golden silk orb-weaver spider to function as a naturally occurring superlens, said to be the first time that a naturally occurring biological material has been used as such a component.

A project at National Yang Ming Chiao Tung University (NYCU) in Taiwan has now made a further advance, creating a highly sensitive fiber optic sugar sensor by coating spider silk with a nanolayer of metal.

As reported in Biomedical Optics Express, the sensor was highly sensitive in the detection of fructose, sucrose, and glucose concentrations. This work may provide a new way to realize precise and sensitive online sugar measurements for point-of-care diagnostics.

"Glucose sensors are crucial to people with diabetes, but these devices tend to be invasive, uncomfortable and not cost-efficient," said NYCU's Cheng-Yang Liu. "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."

The glucose sensors currently used for blood sugar monitoring have a number of potential drawbacks. The skin punctures required can be painful and risk infection, and the tool used to make the puncture can only be used once, making the procedure wasteful.

Fiber-optic sensors detecting glucose via its effects on refractive index are potentially smaller, easy to handle and non-invasive, and could provide a new way to take precise online sugar measurements for point-of-care diagnostics, according to the NYCU team.

Easier testing for sugars, lactose and fat in blood

The project's sensor was manufactured by taking 10-micron silk fiber from Nephila pilipes, a local species of giant wood spider, and coating its surface with first a photocurable resin and then with a nano-layer of gold by sputter deposition, to create a dielectric silk-based optical fiber 100 microns in diameter.

In proof-of-concept trials, the researchers immersed one end of the fiber in liquid samples of fructose, sucrose, and glucose, and connected the other end to a light source and a spectrometer. Recording the transmission spectra as the three sets of sugar solutions passed through the fiber at varying sugar concentrations allowed those concentrations and types of sugar found in the solutions to be assessed.

"The measurement precision and sensing sensitivity we achieved suggests that the sensor can accurately estimate the concentration of an unknown sugar solution," said Liu. "The sensing sensitivity for our proposed sensor completely encompasses the range of sugar concentrations found in human blood."

For use in contact with blood, rather than sugar solutions, the sensor's accuracy and stability under variable environmental conditions will need to be improved, along with extending the length of time the device can be used. Software integrating the senor with mobile devices is another priority, a key requirement for point-of-care readings of sugars in blood and potentially other components such as lactose and fat.

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