New wearable sensor tracks vitamin B6 levels in sweat

Vitamin B6, which is absorbed from a broad range of foods, helps bolster immune system function and neurotransmitters in the brain. But some patients with chronic conditions like diabetes might experience low concentrations of vitamin B6, leading to reduced mental and physical health function, with possible symptoms including irritability, depression, anemia, numbness or muscle twitching. Expensive blood draws are currently the only way to monitor B6 levels, but a team led by Huanyu "Larry" Cheng, the James L. Henderson, Jr. Memorial Associate Professor of Engineering Science and Mechanics at Penn State, has developed a new, non-invasive approach that could allow for continuous monitoring, even at home. 

The researchers created an on-skin sensing platform to detect vitamin B6 in small concentrations of sweat, instead of relying on laboratory tests. The sensor can also detect glucose at a high sensitivity, allowing patients with diabetes to non-invasively monitor glucose and vitamin B6 simultaneously, Cheng said. The team published their approach in Composites Part B: Engineering. 

To create the highly sensitive probe for vitamin B6, Cheng's team produced laser-induced graphene (LIG) nanocomposites - a process that involves patterning atomically thin carbon layers to develop a sensor scaffold upon which they can build the other functional components that target the biomarker of interest. In this study, they used molecularly imprinted polymers (MIPs) to target a very small amount of vitamin B6 present in sweat. 

MIPs are synthetic polymers with pre-defined recognition sites that mimic biological receptors like antibodies to bind to target molecules, Cheng explained. When imprinted in the presence of vitamin B6, MIPs operate as the artificial enzyme that then selectively binds to targets, such as vitamin B6 and glucose, in this case. 

"Since vitamin B6 is a very trace molecule available in the sweat only at small quantities, we had to determine a different approach for detecting it using an artificial enzyme, or MIP," Cheng said. "The MIP in the testing platform binds to the target molecule, giving it a one-to-one process match with a high selectivity to the target molecule, like a toddler fitting a shape into a shape sorter." 

The researchers combined the MIPs with Prussian blue redox probes, a material used to facilitate or indicate reactions and give off an electrical signal in the presence of certain molecules. Together, the MIPs and Prussian blue redox probes underpin the newly developed sensor, which measures vitamin B6 in sweat by detecting changes in electrical current. Typical B6 levels in sweat are around 100 nanomolar, and the sensor has a limit of detection of just .93 nanomolar, which is well within the detectable range. 

Researchers also conducted on-body testing of the sensor for glucose and achieved a limit of detection of 93 nanomolar, which Cheng said is considered highly sensitive compared to other monitors that can detect glucose in sweat.  

"Due to the versatility and adaptability of using MIPs, the sensing platform is versatile and will work to also detect other biomarkers, like glucose," Cheng said. "We would just change the MIP to target other proteins of interest, such as female reproductive hormones or proteins indicating an infectious disease, like sepsis, which we hope to do in subsequent phases of research." 

Monitoring vitamin B6 and other vitamins can be useful for improving patient health, Cheng explained, because fluctuations in vitamin B6 can indicate a compromised immune system. 

"If health care providers detect a large fluctuation of vitamin B6 in the sweat, it can indicate that the patient will be more vulnerable to disease conditions, particularly if they have chronic conditions like diabetes," Cheng said. "The production of antibodies and the corresponding health of the immune system relies on a steady source of B6, so patients could potentially make changes before they get sick." 

The National Institutes of Health, the U.S. National Science Foundation and Penn State supported Cheng's contributions to this research.