Jang, K., Kajale, S.N., Joy, B.C. et al. A wearable device for continuous monitoring of circulating cells at single-cell resolution. npj Biosensing 2, 10 (2025). https://doi.org/10.1038/s44328-025-00032-3

Abstract

Continuous monitoring of circulating cells can revolutionize various medical fields by enabling real-time measurement of clinically important cells’ population. Although methods such as blood drawing-based technology and in vivo flow cytometry (IVFC) have been developed for monitoring circulating cells, they are limited to providing only discontinuous monitoring, which can lead to missing critical treatment windows. Thus, continuous monitoring of circulating cells remains an unmet goal till date. To overcome this challenge, we present CircTrek, a wearable device that for the first time enables continuous monitoring of circulating cells at single-cell resolution and is compatible with cell labeling techniques approved for humans. To ensure wearability, a critical feature for continuous monitoring devices, we custom-designed all necessary circuits and components, resulting in a compact size of 44 mm × 39 mm × 15.5 mm—comparable to a commercial smartwatch. Focused and pulsed excitation light, along with serial electrical filters, are employed to maximize the signal-to-noise ratio (SNR). CircTrek was tested using an in vitro setup which recreates the subcutaneous pulsating blood flow and skin-light interaction in humans. The results demonstrated CircTrek’s ability to detect single cells under the skin phantom, with an average SNR of 11.9. Additionally, the device’s safety and reliability for human use were assessed through simulations and mathematical modeling. CircTrek offers a path to harnessing previously inaccessible information, enabling timely treatments, and supporting accurate clinical decisions with comprehensive real-time data.