Rapid melatonin test can help astronauts and others easily monitor their biological rhythm

PULLMAN, Wash. - A simple test developed at Washington State University could eventually allow astronauts and others in round-the-clock occupations to monitor their biological rhythms in just minutes using a drop of blood, a paper test strip and a smartphone-based reader.

An interdisciplinary team of WSU researchers created an inexpensive, 15-minute test using fluorescent nanoparticles to measure melatonin levels, which rise and fall along with a person's internal biological clock.

That clock orchestrates circadian rhythms, or 24-hour cycles, throughout the body, from digestion and metabolism to brain functioning and alertness levels. Monitoring circadian rhythms is vital in shift work settings - and especially in space operations, where the normal 24-hour rhythms of light and darkness are disrupted and the biological clock becomes dysregulated. This interferes with optimal brain functioning, which in space can make the difference between mission success and disaster.

The work, published in Nanoscale Horizons, describes a melatonin assay integrated with a 3D-printed fluorescence smartphone reader that can quantify melatonin at levels relevant to identifying the start of a person's biological night.

"One motivation for this study is monitoring astronauts' circadian cycles, that's the target," said Annie Du, a research professor in the College of Pharmacy and Pharmaceutical Sciences, and corresponding author of the new publication.

"We focused on developing the sensing method, connected with a smartphone reader that can quantify the result. That is very important because it allows measurements to be taken on the spot, without needing to send blood samples to a laboratory for analysis. The method involves a 'lateral flow immunoassay' based on a paper strip, similar to COVID or pregnancy test strips. The method provides exact melatonin levels, not just a yes or no answer."

The new test can make melatonin testing in space easy and quick. It is the latest of a number of simple test-strip-and-smartphone systems Du has created for monitoring health conditions, including one that allows firefighters and others to quickly check their personal exposure to wildfire smoke. Her work has also focused on developing nanomaterials-based drug delivery techniques for treating cancer, arthritis, and other conditions.

Melatonin is a hormone produced by the pineal gland in the brain, with levels rising in the evening and dropping in the morning. Melatonin thus acts as an internal time cue signaling "physiological nighttime" - knowing when an individual's physiological night begins is useful in scheduling jobs that require high performance at night or over long stretches. It is also important for diagnosing and treating so-called "circadian rhythm sleep disorders," which are caused by problems with the biological clock.

Melatonin concentrations in blood samples are low, making it difficult to detect with conventional techniques. The researchers developed the test-strip method using nanoparticles made of europium, a rare-earth material known for strong fluorescent properties, to improve the sensitivity of the assay.

The fluorescent nanoparticles helped researchers achieve the "gold standard" level of sensitivity for measuring melatonin, an accuracy of up to 10 picograms per milliliter. That level indicates the beginning of an individual's physiological night, the point at which the biological clock no longer promotes alert wakefulness and brain functioning may be compromised.

Researchers are now validating the device by testing plasma samples from individuals studied in WSU's Sleep and Performance Research Center. Eventually, Du hopes the technology can be used to create a continuous melatonin monitoring system, akin to glucose monitoring systems used by people with diabetes.

The project brought together researchers in pharmaceutical science, engineering and sleep science across WSU. Authors on the paper include Zhansen Yang, Xinyi Li, Hans Van Dongen, Yuehe Lin, Yang Song and Dan Du.

This work was partially supported by the NASA-funded state of Washington, Biology in Space Consortium, BioS-ENDURES.

Media Contacts

• Annie Du, WSU College of Pharmacy and Pharmaceutical Sciences, 509-368-6700, [email protected]
• Shawn Vestal, WSU News & Media Relations, [email protected]