Self-powered biosensors that run on urine glucose as fuel can now be embedded into diapers to rapidly and wirelessly monitor urine sugar levels.
What was once viewed as futuristic technologies have now become part of everyday life. From self-driving cars to self-ordering kiosks, science has granted us a wide variety of tools that allow us to live in ease and comfort. In the field of medicine, scientists and clinicians also strive for simplicity and convenience, hence the development of wearable electronics and biosensors that allow medical staff and non-medical people to remotely monitor relevant bodily variables. Such innovations have been especially important for many diabetics who require life-long monitoring of blood sugar levels.
At present, urine sugar levels are being used as a biomarker to obtain information about blood sugar levels. Although it only reveals indirect data, collecting urine sugar is preferable to drawing blood as it is easy, painless, and suitable for elderly and long-term patients. Therefore, scientists have sought to embed wireless sensors into diapers, where it can directly detect and transmit information on urine sugar levels. However, digital devices like sensors and wireless transmitters require an energy source to function. Powering them with batteries is possible, but in practice, installing them in diapers is neither practical nor environmentally sustainable.
Fortunately, a battery-free solution has been proposed in a recent study by scientists from Japan. Associate Professor Isao Shitanda, Professor Masayuku Itagaki, and Mr. Yuki Fujimura from Tokyo University of Science collaborated with Associate Professor Seyia Tsujimura from the University of Tsukuba to develop self-powered diaper sensors that can run entirely on urine glucose. The success of their novel technology rests on a paper-based biofuel cell that converts urine glucose into electricity that powers biosensors.
When Shitanda and colleagues were developing the sensor, they identified several fundamental issues with their proposed solution of using a biofuel cell. They first had to determine the amount of urine needed to generate enough power to fuel the sensor. They also had to find a way to ensure that their device remains stable and durable even for long-term use.
To address the issue of durability, the team developed a special anode using a process called “graft polymerisation.” This technique allowed them to firmly anchor glucose-reactive enzymes and mediator molecules to a porous carbon layer, which served as the base conductive material. With this anode, the scientists were able to construct a paper-based biofuel cell that generates electrical power that is proportional to the amount of glucose in the urine. The fuel cell harnesses the power of electrochemistry and works through a pair of oxidation and reduction reactions.
To determine whether their new biosensor can function as intended, the researchers tested the biosensor in diapers using artificial urine at different glucose concentrations. They used the generated energy to power up a Bluetooth Low Energy transmitter and remotely measured the concentration using a smartphone. Their findings revealed that the biofuel cell could rapidly detect urine sugar within a second, thus validating its potential use for clinical applications.
“Besides monitoring glucose in the context of diabetes, diaper sensors can be used to remotely check for the presence of urine if you stock up on sugar as fuel in advance. In hospitals or nursing care sites, where potentially hundreds of diapers have to be checked periodically, the proposed device could take a great weight off the shoulders of caregivers,” commented Dr. Shitanda.
It is also worth noting that the new sensor is expected to make diaper management more efficient and responsive without compromising the environment. With these strengths, Dr. Shitanda believes that “the concept developed in this study could become a very promising tool towards the general development of self-powered wearable biosensors.”
Source: Shitanda et al. (2021). Self-Powered Diaper Sensor with Wireless Transmitter Powered by Paper-Based Biofuel Cell with Urine Glucose as Fuel. ACS Sensors.