Do you know that female hormones are really important for women's health? Checking these hormone levels in women's body fluids has two major applications. One, it helps them figure out if a woman could have babies and if she's healthy. Two, this test tells us a lot about an individual’s periods, ability to get pregnant, and when menopause might begin.Estradiol is the primary form of the female hormone estrogen, and the most potent and prevalent female hormone during reproductive years. When you're getting ready to release an egg (ovulate) during your menstrual cycle, estradiol gives signals to your body. It's like the conductor of a symphony, telling the orchestra (your hormones) when it's time to play the right notes. Estradiol begins increasing right before ovulation, whereas existing at-home methods like monitoring body temperature or using luteinizing hormone (LH) tests may take longer to reveal what's going on and might not provide as reliable results. Currently, the reliable methods need invasive blood sampling or bulky analytical laboratory equipment. Specially, many individuals will be depressed when faced with the need for frequent hospital visits or multiple daily blood draws. So, when it comes to tracking your fertility, estradiol is like the superhero choice because it gives you the quickest and most accurate info. It's like having a fast and reliable GPS for your baby-making journey!
Well, there's some good news! We propose here a wearable device that can check a female hormone estradiol through your sweat (Figure 1). No needles, no big machines. It's like a small, smart sticker you wear on your skin. This smart sticker can track how your hormone levels change every day, especially during your monthly cycle.
When we started to do this cool thing, it is not easy to realize highly sensitive and selective measurement because estradiol concentration in human sweat is very low (at a few picomolar level). Could we make a sensor to measure estradiol in sweat, even though it's at super tiny level? To address this challenge, we created a special biosensor inside a tiny space (Figure 2a). We put estradiol aptamer which work as a “artificial antibody” inside. It competes with another molecule called "MB-ssDNA," kind of like a little race. When estradiol is around, the aptamer grabs the estradiol molecule and release MB-ssDNA that will move to and recaptured on the surface of working electrodes. The estradiol level can be quantified by measuring the amount of recaptured MB-ssDNA. It is important to note that we used nanomaterials "AuNPs-MXene" in this process, which greatly enhanced the sensitivity due to its high charge transfer efficiency. So, long story short, we made a tiny box with a special race and a magic catcher, and it helps us find estradiol even when it's super tiny.
What's really cool is that we can turn this device into a smart ring. Imagine a comfy, flexible ring on your skin that can measure estradiol in your sweat all on its own. This ring has a special sensor to measure estradiol in your sweat, and it also has other sensors to check things like temperature and pH (Figure 2b). It can even make you sweat a bit locally without the need for you to exercise. We validated this wearable device against gold-standard measurements and tested on participants during their monthly cycles. And guess what? We found that the estradiol levels in sweat matched closely with the ones in blood. So, it's like having a little helper on your skin that tells you all about your female hormones without the hassle!
In a nutshell, we created a wearable system that combines chemistry, materials, and practical devices for non-invasive personalized hormone monitoring. We also discovered a strong link between sweat and blood estradiol levels, and we tracked how sweat estradiol changes during menstrual cycles. We believe that this new technology represents a key advance in the fields of sensors, engineering, and precision medicine.
These results were recently published in Nature Nanotechnology: C. Ye, M. Wang, J. Min, R. Y. Tay, H. Lukas, J. R. Sempionatto, J. Li, C. Xu, W. Gao*, A wearable aptamer nanobiosensor for non-invasive female hormone monitoring, Nature Nanotechnology, 2023, https://doi.org/10.1038/s41565-023-01513-0