Researchers have come up with a method to print nanoparticles like ink, leading to the creation of affordable sweat sensors that can continuously track various molecules.
The future of healthcare may revolve around tailoring treatments to individual needs—figuring out precisely what someone requires and administering the right blend of nutrients, metabolites, and medications as necessary to enhance their health. To achieve this, doctors first need an effective way to continuously assess and track specific health biomarkers.
With this objective in mind, a group of engineers at Caltech has created a technique to inkjet print arrays of unique nanoparticles, enabling mass production of durable wearable sweat sensors. These sensors have the potential to monitor a range of biomarkers, such as vitamins, hormones, metabolites, and medications, in real-time. This allows patients and their healthcare providers to keep track of fluctuations in these substances.
Wearable biosensors utilizing these new nanoparticles have been effectively employed to track metabolites in patients affected by long COVID, as well as to measure chemotherapy drug levels in cancer patients at City of Hope in Duarte, California.
“These are just two instances of what’s achievable,” says Wei Gao, a professor of medical engineering in the Andrew and Peggy Cherng Department of Medical Engineering at Caltech. “There are numerous chronic conditions and their respective biomarkers that these sensors now enable us to monitor continuously and noninvasively,” Gao explains, who is also the lead author of a paper published in the journal Nature Materials detailing the innovative technique.
Gao and his research team characterize the nanoparticles as core-shell cubic nanoparticles. The cubes are created in a solution containing the target molecule the researchers intend to monitor—like vitamin C. As the monomers come together to form a polymer, the target molecule, which in this case is vitamin C, becomes trapped within the cubic nanoparticles. Subsequently, a solvent is utilized to selectively extract the vitamin C molecules, leaving a polymer shell adorned with holes that are precisely shaped to fit the vitamin C molecules—similar to synthetic antibodies that recognize only specific molecular shapes.
Crucially, in this latest research, the team combines these specially constructed polymers with a nickel hexacyanoferrate (NiHCF) nanoparticle core. This material can either be oxidized or reduced when an electrical voltage is applied and comes into contact with human sweat or other bodily fluids. Taking the vitamin C example again, the fluid will interact with the NiHCF core as long as the vitamin C-shaped holes remain unoccupied, generating an electrical signal.
When vitamin C molecules come into contact with the polymer, they fit into these holes, blocking sweat or other bodily fluids from reaching the core. This results in a decrease in the electrical signal. Therefore, the intensity of the electrical signal indicates the concentration of vitamin C present.
“The core is essential. The nickel hexacyanoferrate core remains highly stable, even in biological fluids, making these sensors perfect for long-term monitoring,” explains Gao, who is also an Investigator at the Heritage Medical Research Institute and a Ronald and JoAnne Willens Scholar.
The newly designed core-shell nanoparticles are highly adaptable and can be utilized in printing sensor arrays that assess the levels of various amino acids, metabolites, hormones, or medications in sweat or bodily fluids simply by employing different nanoparticle “inks” in a single printed array. For instance, in the research described in the paper, the team printed nanoparticles that bind to vitamin C alongside other nanoparticles that bind to the amino acid tryptophan and creatinine, a biomarker frequently evaluated for kidney function. All these nanoparticles were combined into a single sensor, which was then mass-produced. These three molecules are significant in studies focusing on patients with long COVID.
In a similar fashion, the researchers also printed nanoparticles-based wearable sensors that specifically targeted three distinct antitumor drugs on separate sensors, followed by testing on cancer patients at City of Hope.
“To showcase the capabilities of this technology, we were able to remotely track the quantity of cancer drugs present in the body at any moment,” Gao states. “This paves the way towards personalizing dosages not just for cancer but for numerous other medical conditions as well.”
Additionally, the paper reveals that the team demonstrated the ability to print sensors that can be implanted just beneath the skin to accurately measure drug levels within the body.
