Biomedical Engineering · us
One Patch Tracks Serotonin and Glucose Simultaneously: Microneedle Sensing Enters the Moving Body
A battery-free wireless microneedle operated continuously for 12 hours on freely moving rats, recording molecular fluctuations associated with stress, feeding, and circadian rhythms; moving from animal experiments to human monitoring still requires overcoming hurdles in accuracy, durability, and clinical significance.
Most health wearables detect heart rate, body temperature, and movement, while the molecular changes that actually help regulate physiology remain hidden beneath the skin. A study published in *Nature Nanotechnology* presents a battery-free wireless microneedle patch that can simultaneously track serotonin and glucose, seeking to move molecular monitoring out of the laboratory and into the everyday context of freely moving animals.
The patch uses microneedles to contact dermal interstitial fluid, avoiding repeated blood draws without requiring complete implantation in the body. Serotonin is recognized by an aptamer sensor, while glucose is measured by an enzyme sensor, with signals then read through wireless electronics. The research team continuously monitored freely moving rats for 12 hours, capturing molecular fluctuations accompanying acute stress, feeding, and circadian changes.
The core of this work is not merely miniaturizing the sensors, but addressing interference caused by movement. When the skin bends, stretches, or is compressed, contact between the microneedles and tissue can change easily, causing electrochemical signal drift. The researchers used a retaining ring and compression structure to mechanically decouple the sensing area from skin deformation. In compression and bending tests on live rats, as well as vibration tests on excised skin, this design maintained stable contact better than fixation with medical tape alone.
The manufacturing method also targets the gap between precision and mass production. The team first used two-photon polymerization to create a high-resolution master mold, then replicated microneedles with tips approximately 430 nanometers wide and hierarchical surface microstructures through ultrasound-assisted molding. Nanostructured gold and platinum electrodes respectively increased the current signal and effective electrochemical surface area, enabling sensing with a single microneedle.
However, these results cannot yet be considered equivalent to a health patch suitable for human use. The study remains an experiment in rats, and 12 hours of data are insufficient to address signal drift, biofouling, skin reactions, and sensor calibration during wear lasting days or weeks. Serotonin in interstitial fluid is also not equivalent to serotonin in the brain; what has been observed so far is that it changes in synchrony with stress or circadian rhythms, and the readings therefore cannot be interpreted directly as indicators of mood or mental state.
If subsequent human studies can confirm the relationship between these measurements and blood or clinical indicators, this type of multiplex molecular patch could potentially provide information beyond that offered by existing continuous glucose monitoring, helping researchers study how metabolism, stress responses, and hormonal signals interact and change in real life. For now, a more accurate characterization is that it is a preclinical platform integrating manufacturability, tolerance of movement, and multiplex sensing—not a product ready for diagnosis or personal health interpretation.