A Multiplexed Microfluidic Platform toward Interrogating Endocrine Function: Simultaneous Sensing of Extracellular...

Extracellular Ca²⁺ ([Ca²⁺]_ex) is an important regulator of various physiological and pathological functions, including intercellular communication for synchronized cellular activities (e.g., coordinated hormone secretion from endocrine tissues). Yet it is rarely possible to concurrently quantify the dynamic changes of [Ca²⁺]_ex and related bioactive molecules with high accuracy and temporal resolution. This work aims to develop a multiplexed microfluidic platform to enable monitoring oscillatory [Ca²⁺]_ex and hormone(s) in a biomimetic environment. To this end, a low-affinity fluorescent indicator, Rhod-5N, is identified as a suitable sensor for a range of [Ca²⁺]_ex based on its demonstrated high sensitivity and selectivity to Ca²⁺ in biomedical samples, including human serum and cell culture medium. A microfluidic chip is devised to allow for the immobilization of microscale subjects (analogous to biological tissues), precise control of the perfusion gradient at sites of interest, and integration of modalities for fluorescence measurement and enzyme-linked immunosorbent assay. As this analytical system is demonstrated to be viable to quantify the dynamic changes of Ca²⁺ (0.2-2 mM) and insulin (15-150 mU L^-1) concurrently, with high temporal resolution, it has the potential to provide key insights into the essential roles of [Ca²⁺]_ex in the secretory function of endocrine tissues and to identify novel therapeutic targets for human diseases.