Naked-eye point-of-care testing platform based on a pH-responsive superwetting surface: toward the non-invasive detection of glucose

Herein, we demonstrate a contact angle (CA)-based naked-eye point-of-care testing platform with rapid pH-responsive superwettability that can switch between superhydrophilic and superhydrophobic properties for quantitative biosensing. The CA of the droplet on the pH-responsive surface approached ~0° at pH 1 and conversely reached 161.4° ± 6.2° at pH 13. We realized the sensitive detection of the pH, urea, and glucose by monitoring the changes in the CA. The traditional invasive diagnosis of diabetes causes pain and brings the risk of infections, such as acquired immune deficiency syndrome (AIDS), hepatitis B, hepatitis C, and syphilis, to the user. To address this issue, we implemented a method for the non-invasive diagnosis of diabetes in human saliva and urine, which avoided the significant drawbacks mentioned above. The accuracy of this method was demonstrated by comparing the results with those from commercial glucometers and theoretical calculations. Interestingly, we successfully monitored glucose levels in sweat before, during, and after cycling. The sensing performance was barely influenced by the temperature, elevation, and droplet color, illustrating promise for expansion to hundreds of millions of potential customers, especially those with color blindness or color weakness. Given its low cost, lack of instruments, and rapid response (within 1 s), this strategy might overcome the limitations of the mechanical stability and durability of superwettable materials and thus might extend the industrial-scale application of bioinspired superwettable systems. Nanostructured surfaces developed by researchers in China enable patients to visualize approximate blood glucose levels for point-of-care diagnostics. The contact angle between the edge of a liquid droplet and the surface on which it sits depends on the interaction between the droplet and the surface. Fan Xia and Jun Dai from the Huazhong University of Science and Technology and their co-workers now harness this concept to develop a simple blood glucose test. The team made a surface by coating a glass substrate with silicon nanoparticles. Acidic droplets or those with low urea or high glucose levels had a small contact angle, giving the droplet a very flat shape. Lower levels of glucose, higher levels of urea or less acidic samples resulted in a more spherical shape. These surfaces could help test for diabetes. A pH-responsive superwetting surface is fabricated and applied as a point-of-care testing platform for naked eye biosensing. Because of the outstanding switching between superhydrophilicity and superhydrophobicity, contact angle based biosensing method is developed for pH, urea, and glucose detection. Especially, non-invasive detection of glucose is achieved for diabetes diagnosis and exercise monitoring. Given to its low cost, instrument-free, disposable, and rapid response (within 1 s), this strategy not only provides a universal platform of point-of-care testing but also extends the industrial-scale application of bioinspired superwettability systems.