Israeli and Dutch scientists have developed two biometric watches − one that measures glucose and hydration levels, the other pulse − that use changing patterns of scattered light to monitor physiological parameters. According to the authors of the paper, described in The Optical Society’s (OSA) journal Biomedical Optics Express, the glucose-monitoring watch is the first wearable sensor that can measure glucose levels in a non-invasive fashion.
The wearable biometric systems were created by researchers from Bar-Ilan University in Israel and the Deft University of Technology in The Netherlands. They both use the ‘speckle effect’, where interference patterns are produced on images when laser light reflects from an uneven surface or scatters from an opaque material. The scattering patterns of light change when the material that the laser reflects or scatters off is moving, for example as blood flows through blood vessels. ‘The speckle pattern changes with changes in the flow,’ said Mahsa Nemati, a biomedical engineer from the Optics Research Group at Deft University of Technology in The Netherlands.
The wearable glucose sensor, which measures glucose concentration and hydration levels, consists of a laser that produces a wavefront of light to illuminate the skin and nearby arteries on the wrist, and a camera that monitors changes in the light as it scatters off the skin. Because glucose, unlike other blood components, demonstrates a ‘Faraday effect’ − whereby the polarisation of the wavefront is altered under the presence of an external magnetic field (produced by a magnet in the watch) − the glucose concentration can be directly measured by examining these changing patterns (see figure 1).
Schematic diagram showing the set-up of the glucose-monitoring wearable device. Credit: Biomedical Optics Express
The rehydration levels are measured because the strength of the signals produced are affected by muscle weakness, one of the major signs indicating mild to moderate dehydration.
Zeev Zalevsky of Israel’s Bar-Ilan University and his team would like to now minimise the margin of error of the readings from the device. ‘Around 96 per cent of our in vivo measurements were within a range of 15 per cent deviation from the readout of a medical reference glucometer device,’ Zalevsky explained. ‘The main factor for errors now is the stability of our device on the wrist of the user. We are currently investing efforts in deriving proper calibration and motion cancellation procedures that will allow us to reduce this sensitivity.’
It is anticipated that the scientists will be able to produce a commercial device and enter the market within the next two or three years. According to Zalevsky, the wearable watch is a major step towards non-invasive, continuous in vivo measurement of glucose, which would have a beneficial effect on the medical field. ‘Glucose is the holy grail of the world of biomedical diagnostics, and dehydration is a very useful parameter in the field of wellness, which is one of our main commercial aims,’ Zalevsky pointed out
The second biometric device, which monitors pulse, was developed by Mahsa Nemati of Delft University of Technology in conjunction with Philips Research, could be the first wearable device to measure pulse without being affected by movement.
The team simulated heartbeats in milk and took pulse measurement from the finger of a volunteer, and discovered that the speckle effect could be used to measure flow pulsations even when the light source used to create the speckle pattern was moving.
‘This paper shows for the first time that a speckle pattern generated from a flowing liquid can give us the pulsation properties of the flow in spite of motion-induced artefacts,’ explained Nemati. ‘Sophisticated optics is not necessary to implement this, so the costs for devices can be kept low. Another advantage is that the devices can be non-contact or far from the sample.’
The scientists are now collaborating with sensor companies to integrate the pulse-monitoring method into existing sensors, to be used in clinical or sport applications, Nemati added.