Researchers from ICFO-The Institute of Photonic Sciences have developed the next generation flexible, transparent wearable. These wearables can noninvasively, continuously and accurately monitor multiple vital health signs. These non-invasive, comfortable wearables using optical based sensor are capable of measuring respiration rate, heart rate, arterial oxygen saturation and exposure to UV radiation from the sun. An advantage of this device is that it can be charged wirelessly through a mobile phone which means it can function without a battery. The parameters measured by the device can be visualized and stored on a mobile phone which is connected to it by Bluetooth.
Monitoring of vital health signs with non invasive devices are becoming popular not just for fitness monitoring but also for the early detection and prevention of common health problems like hypertension, heart failure, stress related complications. Such wearable non-invasive technologies, especially the ones based on optical detection, are drawing attention for the improvement of public health. Presently wearable devices use rigid and non flexible components which is its drawback. Currently available devices also track a limited number of vital signs and do not have the accuracy. The flexible wearable device developed by the research team, which uses optical detection mechanism, can non-invasively track the body’s internal function has overcome the drawbacks of its predecessor.
Currently available wearable electronic devices use the skin, which is a unique medium for electronic devices to monitor wellness and health status of the body, to measure vital health signs. Devices which use optical detection mechanism have great demand since they non-invasively track one’s health status. Photoplethysmography (PPG), a powerful, non-invasive technique, which functions by sending light of a certain wavelength into the skin forms the basis of optical vital sign monitoring mechanism. Commercial consumer devices already use the PPG technique to measure the heart rate and arterial oxygen saturation. These devices which are already available are made out of rigid silicon photodiodes which make them non flexible so they cannot interact with the skin properly which reduces the accuracy of the data measured. Also such rigid and non flexible devices can be worn in limited areas on the body. Thick, visible bulky sensors with rigid sensors are neither comfortable to wear nor aesthetical pleasing hence have a lesser demand from consumers.
Researchers from ICFO by integrating GQD (graphene sensitized with semiconducting quantum dots) photodetectors (PDs) on flexible substrates have created the next generation flexible and transparent comfortable wearable devices. Graphene being transparent and flexible is a potential candidate for wearable sensors.
By creating a number of flexible prototypes the researchers have demonstrated a wide range of potential applications for their advanced light sensing technology by integrating GQD PDs into health-tracking wearables. The various prototypes include flexible and transparent wearable bracelet, health patch on mobile phone and near-field communication (NFC) circuitry for tracking health signs and exposure of skin to ultraviolet (UV). According to the researchers the prototype can provide real time and continuous measurements.
Flexible and transparent wearable bracelet:
The team had incorporated a flexible light sensor into the bracelet which can optically record changes in volume of blood vessels due to the cardiac cycle. It can then decipher various vital signs like heart rate, respiration rate and blood pulse oxygenation. According to the researchers the bracelet has been designed to adapt to the skin surface in such a manner so that it can continuously measure even during physical activity.
Health patch on mobile phone screen:
The team had integrated a graphene health patch on a mobile phone screen to fabricate the heart patch. The heart patch is capable of instantly measuring and displaying real time vital signs whenever a user places a finger on the screen. A distinctive property of the prototype is that it operates with ambient light which leads to lower power consumption thereby health signs can be monitored continuously over a long period of time.
The researchers have taken their technology to the next level by extending its functionality beyond the visible range. Based on the same core technology they integrated the GQD PDs into the NFC antenna circuitry to develop a flexible wearable UV patch. The patch is capable of detecting environmental UV index. It operates without a battery and is capable of wireless data and power transfer. The patch can detect UV radiation efficiently. It can be used to track radiation from the sun in order to warn the user of overexposure. This flexible wearable UV patch can be attached to the skin or clothes.
ICFO researchers have used two types of nanomaterials to develop this advanced light sensing technology. Transparent and highly flexible nanomaterial graphene, made of one-atom thick layer of carbon atoms, was combined with the other nanomaterial a light absorbing layer of quantum dots to make a graphene-quantum-dots-based device which formed the basis of the technology developed to give flexibility and design freedom to wearables. The researchers designed the wearable based on graphene light sensing components by utilizing the advantages of both flexible and rigid components. For vital sign sensing they used the flexible components on the other hand they used the benefits of high performance and miniaturization of conventional rigid electronic components.
They have overcome another drawback of the currently available devices which require amplifiers. By overcoming this drawback the team has achieved a large degree of design freedom. Thus the device can be used to efficiently and precisely measure vitals not only on the finger and arms but also on the forehead, foot and chest. Since the team has established a broad wavelength detection range of the device the team intends to increase the number of vital signs that can be monitored with this wearable. The team is optimistic they could further develop the device to measure vitals such as hydration and muscle microvascular blood oxygenation.
As claimed by the research team their scalable, low-power device is capable of overcoming the challenges and meeting the demands of the expanding wearable industry. The researchers have proposed that the flexible GQD assembly may be seamlessly integrated into jewellery, headwear, footwear and garments making it a unique application of the technology which will be of great demand. Comfortable wearable flexible devices which can monitor bodily functions are on top priority for users. Thus researchers are optimistic this device will be attractive to them.
Emre O. Polat, Gabriel Mercier, Ivan Nikitskiy, Eric Puma, Teresa Galan, Shuchi Gupta, Marc Montagut, Juan José Piqueras, Maryse Bouwens, Turgut Durduran, Gerasimos Konstantatos, Stijn Goossens, Frank Koppens. Flexible graphene photodetectors for wearable fitness monitoring. Science Advances, 2019; 5 (9): eaaw7846 DOI: 10.1126/sciadv.aaw7846
Available from: https://advances.sciencemag.org/content/5/9/eaaw7846