Higher Education Press Dec 27 2024 Mitochondrial calcium signaling is crucial for energy metabolism and calcium homeostasis, but monitoring it accurately is challenging due to pH fluctuations. Existing GECIs are often sensitive to pH changes, leading to artifacts and inaccurate measurements. Additionally, the limited availability of cyan fluorescent GECIs hinders multiplexed imaging. Building on the bright cyan fluorescent protein mTurquoise2, TurCaMP offers an inverse response to Ca2+