Non-invasive glucose sensor could eliminate painful procedures

People living with diabetes monitor and manage their condition by checking glucose levels in their blood via a finger pin prick to draw blood or by wearing adhesive microneedles. In addition to being painful, these methods can cause itching, inflammation and infection.

Now, researchers at TMOS, the Australian Research Council Centre of Excellence for Transformative Meta-Optical Systems, believe they have taken a significant step towards eliminating this discomfort.

Their RMIT University team has discovered new aspects of glucose’s infrared signature and used this to develop a miniaturised optical sensor measuring 5mm in diameter that could one day be used to provide continuous non-invasive glucose monitoring in diabetes management.

Non-invasive glucose sensing has been a target for almost 30 years due to its implications for pain free monitoring. Optical glucose sensing techniques have been reported; but they require complex optical instrumentation usually found in laboratories, making them unsuitable for regular patient use.

According to the team, the primary challenge in developing affordable, wearable optical glucose testing has been miniaturisation and filtering out the glucose signals from water absorption peaks in the near infrared (NIR) spectrum. Until now, it has been almost impossible to accurately differentiate between water and glucose in the blood.

In first-of-its-kind research, published in Advanced Sensor Research, the team has identified four infrared peaks in glucose that allow selective and sensitive identification in aqueous and biological environments. 

The team has fabricated a miniaturised glucose sensor established on a 1600-1700nm waveband that is Bluetooth enabled and operates using a coin battery, which allows for continuous glucose monitoring.

This compact sensor is said to have demonstrated its viability detecting glucose levels in the human body range from 50 to 400mg/dL in blood plasma, with a comparable limit of detection and sensitivity to larger, laboratory-based sensors. Its small dimensions could see it one day integrated into smart watches and other pain-free wearable health trackers.

In a statement, lead author, RMIT PhD scholar Mingjie Yang, said: “Until now, there is no consensus on the unique spectroscopic signature of glucose, largely because the O-H bonds targeted in near-infrared spectroscopy for glucose detection are also abundant in water. This similarity makes it challenging to distinguish between glucose and water signals, especially in complex biological fluids and tissues.

“We optimised spectroscopy setup and analysed transmittance to identify peaks unique to glucose. Our discovery finally provides the information necessary to move forward with miniaturised optical glucose sensing and we have developed a device prototype to suggest the foundation for futuristic non-invasive glucose sensor.”

The device prototype utilises a surface-mounted device light emitting diode (SMD LED) and circuits made of thin-film copper coated polymide (Cu/PI) 110 microns thick that was developed with a laser patterning technology.

According to TMOS, the millimetre-scale and lightweight design of this device makes it ‘considerably more compact’ than traditional benchtop spectrophotometers. Furthermore, the flexible patch-like design offers the future possibility of direct reading as a wearable device on human skin.

The performance of the device has been evaluated using aqueous glucose solutions and blood plasma. Computational analysis of light-skin interference has been conducted that indicate how the SMD LED will penetrate the skin. Simulation results suggest the promising locations for future exploration of optical glucose sensing in clinical setups.

RMIT University has filed a patent application related to the optical glucose sensor technology and the team is keen to collaborate with academic and industry partners to continue this work.