A Groundbreaking Wearable Sensor Achieves an Unprecedented Level of Solar Power Efficiency
Sweat, akin to blood, holds valuable insights into an individual’s health, and fortunately, its collection is much less intrusive. This forms the foundation for the creation of wearable sweat sensors, crafted by Wei Gao, an assistant professor of medical engineering, Heritage Medical Research Institute Investigator, and Ronald and JoAnne Willens Scholar.
Expanding Substance Measurement and Health Risk Evaluations
During the last five years, Gao has continuously enhanced his wearable devices, enabling them to measure various substances such as salts, sugars, uric acid, amino acids, and vitamins. Additionally, these devices can now detect more intricate molecules like C-reactive protein, offering timely evaluations of specific health risks. Recently, Gao collaborated with Martin Kaltenbrunner’s team at Johannes Kepler University Linz in Austria to integrate flexible solar cells, providing power to these advanced biosensors.
Gao’s lab employs a solar cell constructed from perovskite crystal, a material characterized by the same chemical structure as calcium titanium oxide. Perovskite has garnered considerable attention among solar cell developers due to several advantages
To begin with, it offers a more cost-effective manufacturing process compared to silicon, which has been the primary material in solar cells since the 1950s and requires extensive purification procedures.
Secondly, perovskite solar cell layers are exceptionally thin, almost “quasi-2D” in Gao’s terms, being up to 1,000 times thinner than silicon layers.
Light spectra
Moreover, perovskite can be tailored to different light spectra, ranging from outdoor sunlight to various indoor lighting conditions.
Most importantly, perovskite solar cells boast a higher power conversion efficiency (PCE) than silicon, signifying their ability to convert a larger portion of received light into usable electricity.
While silicon solar cells typically achieve PCE levels ranging from 26 to 27 percent, their practical usage usually stays within 18 to 22 percent. In contrast, Gao’s wearable sweat sensor equipped with a flexible perovskite solar cell (FPSC) sets a groundbreaking record with a PCE exceeding 31 percent, specifically under indoor light illumination.
According to Gao, the objective is not solely reliant on harnessing strong sunlight to energize their wearables. Instead, they prioritize real-life scenarios, encompassing typical office and home lighting conditions. Gao highlights that numerous solar cells may exhibit high efficiency in bright sunlight but falter in weaker indoor lighting settings. However, the FPSC integrated into the sweat sensor proves highly suitable for indoor lighting due to its excellent spectral response, closely aligned with the emission spectrum of common indoor lighting.
Challenges with Lithium-ion Batteries and Silicon Solar Cells
Earlier versions of Gao’s wearable sweat sensors relied on bulky lithium-ion batteries, necessitating recharging with an external power supply. To find a lighter and more sustainable electricity source for these high-demand devices, Gao’s team explored the use of silicon solar cells, but found them to be inflexible, inefficient, and reliant on strong lighting conditions.
They also experimented with harnessing energy from chemicals present in human sweat, considering it a readily available biofuel, as well as from body motion. However, these approaches proved unstable or demanded too much effort from the wearer.
Extended Wear and Enhanced Biomarker Monitoring
The adoption of FPSCs has revolutionized Gao’s sweat sensors, allowing them to be worn continuously for 12 hours a day. These sensors provide uninterrupted monitoring of pH, salt, glucose, and temperature, along with periodic monitoring (every five to 10 minutes) of sweat rate. Notably, all of these functionalities are achieved without the need for batteries or a specially dedicated light source. Additionally, the use of a lighter and less cumbersome power source has opened up space in the wearable for more detectors, enabling the simultaneous monitoring of a greater number of biomarkers.
Multi-layered Construction and Four Interacting Components
Similar to its predecessors, the novel wearable sweat sensor is constructed using an origami-like approach, incorporating distinct layers for different functions. The sensor comprises four key interacting components:
- Power management: This component efficiently distributes the electricity obtained from the integrated solar cell.
- Iontophoresis: The second component induces sweating without requiring any physical exercise or exposure to high temperatures from the wearer. In Gao’s study, iontophoresis was conducted every three hours to ensure a continuous supply of sweat for monitoring biomarkers.
- Electrochemical measurement: The third component facilitates the measurement of various substances present in the sweat.
- Data processing and wireless communication: The fourth component manages data processing and wireless communication, enabling the sensor to interface with a cellphone app, displaying real-time monitoring results.
Once fully assembled, the sensor measures 20 x 27 x 4 millimeters and can endure the mechanical stress associated with being worn on the body. Gao emphasizes that many elements of the sweat sensor, such as the electronics and FPSC, are reusable, with the exception of the disposable sensor patch. This patch can be mass-produced at a low cost using inkjet printing, allowing for customization based on the user’s desired substances to be measured in their body.
The application of these solar-powered sweat sensors extends far beyond the capabilities of current fitness or health trackers. They have the potential to measure a wide range of parameters. For instance, they can aid in diabetes management, as studies have indicated that glucose levels in sweat closely correlate with blood glucose levels. Additionally, these sensors can detect various conditions like heart disease, cystic fibrosis, and gout.
Enabling Precise Monitoring of Cortisol, Hormones, and Metabolites
Their noninvasive nature and ability to conduct multiple measurements in short intervals allow them to establish an individual’s baseline for substances such as cortisol, hormones, or metabolites of different nutrients and medications.
Once these baseline levels are established, any future deviations can serve as a more effective diagnostic indicator compared to a single blood draw. Moreover, due to their relatively low cost, there is optimism that these sensors can become valuable diagnostic tools globally, including in developing countries.
Read the original article on: Tech Xplore
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