Researchers have exploited the light-guiding properties of spider silk to develop a sensor capable of detecting and measuring small changes in the refractive index of a biological solution, including glucose and other types of sugar solutions. The new light-based sensor could one day be useful for measuring blood sugar and other biochemical analytes.
“Glucose sensors are essential for people with diabetes, but these devices tend to be invasive, uncomfortable and uneconomical,” said research team leader Cheng-Yang Liu of National Yang Ming University. Chiao Tung in Taiwan. “With spider silk attracting attention for its superior optomechanical properties, we wanted to explore the use of 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 the journal Optica Publishing Group Express Biomedical Optics. They show that it can be used to determine the concentrations of fructose, sucrose and glucose sugars based on changes in the refractive index of a solution. Spider silk is ideal for this application because it can not only transmit light like an optical fiber, but it is also very strong and elastic.
“Our novel spider silk-based fiber optic sugar sensor is convenient, compact, biocompatible, economical, and highly sensitive,” Liu said. “With further development, this could lead to better home health monitoring devices and point-of-care diagnostic and testing devices.”
From silk to sensor
To make the sensor, the researchers harvested dragline spider silk from the giant wood spider. Pilipes of Nephila, originally from Taiwan. They wrapped the silk, which is just 10 microns in diameter, in a biocompatible photo-curable resin and hardened it to form a smooth protective surface. This created a fiber optic structure 100 microns in diameter, with the spider silk serving as the core and the resin as the sheath. They then added a nano-layer of biocompatible gold to improve the fiber’s sensing capabilities.
This process formed a wire-like structure with two ends. To use the fiber to take measurements, the researchers immersed one end in a liquid sample and connected the other end to a light source and a spectrometer. This 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,” Liu said. “Additionally, because it is compact, it could provide access to hard-to-reach areas such as the brain and heart. With further development, it is also hoped that this silk-based fiber optic sugar sensor may be used in implantable medical devices and treatment strategies in biomedical applications.
Consistent and accurate readings
To test the sensor’s repeatability and stability over time, 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 5 minute intervals.
To quantitatively determine the performance of the silk-based fiber 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 both identify the type of sugar in the solution and provide a reading of the concentration.
“The measurement accuracy and detection sensitivity we obtained suggests that the sensor can accurately estimate the concentration of an unknown sugar solution,” Liu said. “Furthermore, the detection sensitivity of our proposed sensor completely encompasses the range of sugar concentrations found in human blood.”
Before the sensor can be used for real-time measurements in a clinic or home-use device, it will be necessary to improve its accuracy and stability in the face of 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 expand the functionality of the sensor so that it can be used to measure different biochemical components in human blood, such as lactose and fats.