Calcium plays an important role in the heart’s function. The calcium ions regulate the muscle proteins that initiate contraction, helping the heart pump efficiently and maintain a regular rhythm.

Making sure the heart cells have the proper amount of calcium is crucial. Not enough could lead to arrhythmias or sudden heart failure, while too much, known as calcium overload, can result in a heart attack, stroke, or other cardiac incidents.

Knowing a patient’s calcium levels is key to proper care. New research by Northwestern Engineering’s Igor Efimov could be a step toward instantly unlocking that and other knowledge about the heart.

Efimov and collaborators at George Washington University from Luyao Lu’s lab have produced a new wireless device that measures multiple heart functions at the same time. The device uses advanced technology to combine tiny electrodes, lights, and sensors into a flexible structure. Through small animal testing, the team found the device can accurately measure electrical signals and calcium levels in the heart, with applications in both treating patients and advancing research on the progression of cardiac diseases.

“The data we are measuring are crucial for understanding how the heart works. The device works well with living tissue and can help study normal heart rhythms, irregular heartbeats, and treatments,” Efimov said. “The technology could greatly benefit heart research and improve diagnosis and treatment of heart diseases.”

Efimov is a professor of biomedical engineering at the McCormick School of Engineering and a professor of medicine (cardiology division) at the Feinberg School of Medicine. He presented his work in the paper “A Soft Multimodal Optoelectronic Array Interface for Multiparametric Mapping of Heart Function in Vivo,” published February 7 in the academic journal Science Advances. Lu, an associate professor at George Washington University who was trained at Northwestern University, co-led the research with Efimov.

One of the goals of Efimov’s lab is to develop novel implantable, interventional, and wearable bioelectronic devices for real-time device-based diagnostics and therapy of heart diseases and sudden cardiac death.

Building on this work, the team’s device relies on fluorescence microscopy, a technique to visualize molecular changes in living animals. The implant uses advanced materials — conductive silver nanowires coated with gold for improved signal transmission and a system of light-emitting diodes (LEDs) and photodiodes — designed to be sensitive to a calcium-responsive protein. The LEDs illuminate heart tissue, and the photodiodes collect fluorescence emitted by the calcium-responsive protein. This design allows the device to monitor calcium concentration and track electrical signals with each heartbeat, providing real-time insights into cardiac function.

“We can measure electrophysiology, mechanics, signaling, metabolism, and on and on,” Efimov said.

Currently, there are many devices used to monitor heart health, such as implantable pacemakers and defibrillators, stents, and artificial valves. These devices feature electronic components with sensors that track cardiac activity and allow them to adjust accordingly to the heart’s needs depending on the amount of stress, such as increased exercise.

Instead of relying on physiological parameters to prompt a device to kick in, Efimov said his team’s fluorescence-based system could be applied to existing monitoring devices to predict cardiac events before they happen. He said that doctors, hospitals, and patients could quickly access data coming from the sensor, allowing early treatment to fight potentially fatal conditions.

“There's monitoring all the time,” Efimov said, “so a physician or some system will be alerted that a patient is at risk of sudden death.”