Researchers at UCLA have developed a fingertip sensor that can rapidly provide data on the levels of lithium in the body. Used as a treatment for bipolar disorder and depression, lithium requires very accurate and sensitive dosing, with too little providing no therapeutic benefit but slightly too much potentially leading to unwanted side-effects. At present, the most common method to assess lithium levels involves a blood draw and subsequent lab testing, which is inconvenient and cumbersome. The new electrochemical sensor incorporates a hydrogel pad that facilitates the sensitive measurements, which require an aqueous environment. An ion-selective electrode detects the lithium ions present in the sweat on the fingertip, providing a result in as little as 30 seconds.
Lithium can be a very effective treatment for bipolar disorder, but it is tricky to get the dose just right to maximize its therapeutic properties while reducing the risk of potentially dangerous side-effects. Another issue with the drug is the potential for poor patient compliance. If a patient misses some doses and their medication does not appear to be working, a clinician typically must perform a blood draw and order a lab test to see if lithium levels are out of whack. This is time consuming, invasive, and expensive.
To address this, these researchers have created a tiny fingertip sensor that can measure the levels of lithium in sweat. “Although it may not be visible, the human body constantly produces sweat, often only in very small amounts,” said Shuyu Lin, one of the creators of the new sensor. “Small molecules derived from medication, including lithium, show up in that sweat. We recognized this as an opportunity to develop a new type of sensor that would detect these molecules.”
The tiny sensor can detect lithium in sweat from a fingertip, although the small amount of sweat that is typically present in that location provided a challenge, as the electrodes in the sensor require an aqueous environment to function. To achieve this, the researchers incorporated a hydrogel on the sensor surface, which creates these conditions. The gel includes glycerol, which helps to prevent it from drying out.
An ion-selective electrode detects the lithium ions, using a paired reference electrode to calculate a difference in electrical potential that indicates the concentration of lithium in the sweat sample. The device can deliver results in as little as 30 seconds.
“Through a single touch, our new device can obtain clinically useful molecular-level information about what is circulating in the body,” said Sam Emaminejad, another researcher involved in the study. “We already interact with a lot of touch-based electronics, such as smart phones and keyboards, so this sensor could integrate seamlessly into daily life.”
The researchers presented their technology at the 2022 fall meeting of the American Chemical Society (ACS).