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Non-Invasive Touch-Based Sensor Detects Lithium Levels from Sweat

Lithium can help with the symptoms of both bipolar illness and depression if used at the proper dosage. Amounts that are either too little or too much can have harmful effects. Patients must submit to invasive blood tests to precisely monitor the level of this medicine in the body.

Non-Invasive Touch-Based Sensor Detects Lithium Levels from Sweat

Image Credit: Jade ThaiCatwalk/

Researchers describe the creation of a tiny sensor that, without the need for a trip to the doctor, can quickly and accurately detect the level of lithium in sweat on the surface of a fingertip.

The researchers report their findings at the American Chemical Society’s (ACS) fall meeting. ACS Fall 2022 is a hybrid conference that will be held online and in person from August 21–25, with on-demand access available from August 26th to September 9th. Nearly 11,000 talks covering a wide range of science issues are included in the meeting.

Lithium must be taken at a certain dosage, and patients frequently struggle to take medication as directed and may forget pills. Therefore, health care professionals need to be aware of how much medication the patient is taking when the medication does not seem to be working. But the monitoring options available today have some serious shortcomings.

For instance, blood tests are intrusive and time-consuming, but they yield accurate findings. In contrast, pill counters do not actually track how much medication is consumed. The group decided to use another bodily fluid to overcome these restrictions.

Although it may not be visible, the human body constantly produces sweat, often only in very small amounts. 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,” adds Shuyu Lin Ph.D., a postgraduate student researcher who is co-presenting the work with graduate student Jialun Zhu at the meeting.

Through a single touch, our new device can obtain clinically useful molecular-level information about what is circulating in the body. 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.

Sam Emaminejad PhD, Project Principal Investigator, University of California, Los Angeles

The development of a sensor to detect lithium, however, caused significant technical difficulties. Small amounts of sweat are typically present, but an aqueous, or watery, environment was necessary for the electrochemical sensing required to identify charged particles of lithium.

The scientists created a glycerol-containing water-based gel to deliver it. This additional component kept the gel from drying up and created a regulated environment for the sensor’s electronic components.

The scientists utilized an ion-selective electrode to capture the lithium ions after they had passed through the gel. A differential in electrical potential between the accumulating ions and a reference electrode is produced.

The difference allowed the researchers to determine the amount of lithium in sweat. These parts come together to form a tiny, rectangular sensor that can detect lithium in about 30 seconds and is a little larger than the head of a thumbtack. The sensor is still undergoing preliminary testing, but eventually, the researchers hope to integrate it into a bigger yet-to-be-designed system that gives the patient or provider visual input.

The team first characterized the sensor using a synthetic fingertip before getting real people to test it, including one who was receiving a lithium treatment regimen. The levels of lithium in this person were measured before and after the drug was administered. They discovered that these readings were fairly close to those obtained from saliva, which previous studies have demonstrated to be an accurate way of determining lithium levels. The researchers intend to investigate how lotion and other skin care items affect the sensor’s results in the future.

There are uses for this technology that go beyond lithium. In addition to monitoring alcohol and acetaminophen, a painkiller also known as Tylenol®, Emaminejad is developing comparable touch-based sensors to monitor other substances.

A robotic distribution system that only distributes medication when the patient has a low level in their bloodstream, or encryption protected by a fingerprint for substances that are easy to abuse, might be included in the full sensing systems.

The National Science Foundation, the Brain and Behavior Foundation, Precise Advanced Technologies and Health Systems for Underserved Populations, and the UCLA Henry Samueli School of Engineering and Applied Sciences have all provided funding and assistance to the study.

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