#biosensors

Researchers create biosensor by turning spider silk into optical fiber

Researchers have harnessed the light-guiding properties of spider silk to develop a sensor that can detect and measure small changes in the refractive index of a biological solution, including glucose and other types of sugar solutions. The new light-based sensor might one day be useful for 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 in Taiwan. "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 ideal for this application because it can not only transmit light like an optical fiber but is also very strong and elastic.

Brain Recording Bettered

Mapping electrical activity in the brain during surgery helps doctors determine which parts are functioning, which maybe diseased, and which bits are safe to remove or treat. The surgeon places a flexible sensor – arranged as a grid of typically 16 to 64 channels – directly onto the cortex to get the most accurate readings possible. But while such sensors can resolve electrical signals to approximately the nearest centimetre, a newly developed one (pictured) is set to provide 100x better resolution – to the nearest millimetre. The new sensor has 1024 channels (in a 3.2cm square grid) or 2048 (in an 8cm square) and is made from thinner, more flexible material than previous iterations to enable a better fit to the contours of the cortex. In short, if this device can be proven safe for clinical use it would give brain surgeons unprecedented accuracy in determining borders between healthy and unhealthy tissue.

Written by Ruth Williams

Image by David Baillot, UC San Diego Jacobs School of Engineering

Integrated Electronics and Biointerfaces Laboratory, Department of Electrical and Computer Engineering, University of California San Diego, La Jolla, CA, USA

Image copyright held by the original authors

Research by Youngbin Tchoe, Andrew M Bourhis & Daniel R Cleary, et al Published in Science Translational Medicine, January 2022

Alice Gillen and Nils Schürgers, two of the paper’s authors, making sensor gels out of the new DNA-nanotube complexes. Credit: Alessandra Antonucci

Biosensors are devices that can detect biological molecules in air, water, or blood. They are widely used in drug development, medical diagnostics, and biological research. The growing need for continuous, real-time monitoring of biomarkers in diseases like diabetes is currently driving efforts to develop efficient and portable biosensor devices.

Some of the most promising optical biosensors currently being developed are made using single-walled carbon nanotubes. The near-infrared light emission of the carbon nanotubes lies within the optical transparency window of biological materials. This means water, blood, and tissue such as skin do not absorb the emitted light, making these biosensors ideal for implantable sensing applications. These sensors can thus be placed underneath the skin and the optical signal can still be detected without the need to have electrical contacts piercing through the surface.

However, the omnipresence of salts in biofluids creates a pervasive challenge in designing the implantable devices. Fluctuations in salt concentrations that naturally occur in the body have been shown to affect the sensitivity and selectivity of optical sensors based on single-walled carbon nanotubes wrapped with single-stranded DNA.

In order to overcome some of these challenges, a team of researchers from the lab of Ardemis Boghossian at EPFL engineered stable optical nanotube sensors using synthetic biology. The use of synthetic biology imparts increased stability to the optical biosensors, making them more suitable for use in biosensing applications in complex fluids such as blood or urine and even inside the human body.

“What we did was wrap nanotubes with ‘xeno’ nucleic acids (XNA), or synthetic DNA that can tolerate the variation in salt concentrations that our bodies naturally undergo, to deliver a more stable signal,” says Ardemis Boghossian. Alice Gillen, the lead author of the paper, led the efforts in studying how certain salts affect the optical emission of the biosensors.

The study covers varying ion concentrations within the physiological ranges found in common biofluids. By monitoring both the intensity of the nanotubes’ signal and shifting of the signal’s wavelength, the researchers were able to verify that the bioengineered sensors showed greater stability over a larger range of salt concentrations than the DNA sensors traditionally used in the field.

“This is really the first time a true synthetic biology approach is being used in the field of nanotube optics,” says Boghossian. “We think these results are encouraging for developing the next generation of optical biosensors that are more promising for implantable sensing applications such as continuous monitoring.”

Source : EPFL