Multifunctional aggregation-based fluorescent probe for visualizing intracellular calcium dynamic fluctuations

Calcium ion (Ca²⁺) is an indispensable second messenger in living organisms. The impaired Ca²⁺ handling can induce many diseases. In this paper, we developed a simple and effective method to encapsulate a coumarin-based Ca²⁺ probe ((E)-2-hydroxy-N'-((7-hydroxy-2-oxo-2H-chromen-8-yl)methylene)-2-phenylacetohydrazide, CPM) into nanoparticles (NPs), and CPM NPs with blue fluorescence were obtained, whose maximum excitation and maximum emission wavelengths were characterized at 365 nm and 450 nm, respectively. The CPM NPs show significant fluorescence enhancement toward Ca²⁺ over other metal ions, with a limit of determination (LOD) of 0.04 μM. To optimize the optical property of the NPs, CPM and curcumin, which were introduced as the Förster resonance energy transfer (FRET) donor and acceptor, respectively, were co-encapsulated, and bright green CPM@Cur NPs with large stokes shift and narrow emission band width were constructed. Due to their low cytotoxicity and excellent stability, CPM NPs and CPM@Cur NPs were further successfully used to discriminate the primary aortic smooth muscle cells isolated from mice with abnormal Ca²⁺ homeostasis from their littermate controls. It is worth noting that CPM@Cur NPs exhibit stronger fluorescence signal and diminished background interference, which make them have great potential in the Ca²⁺ monitoring during biological processes. This strategy opens a new way to synthesize NPs with high brightness and has a potential application prospect in composite sensing and intracellular imaging. CPM@Cur NPs are developed and applied in biological sensing and intracellular Ca²⁺ imaging, as well as discriminating the cells with abnormal calcium homeostasis.