Capsicum-Derived Biomass Quantum Dots Coupled with Alizarin Red S as an Inner-Filter-Mediated Illuminant Nanosystem for Imaging of Intracellular Calcium Ions

Calcium ion (Ca²⁺) plays crucial roles in the signal transduction pathways associated with various physiological and pathological events. Monitoring intracellular Ca²⁺ is of great significance for cell biology research. Here, we report the use of biomass quantum dots (BQDs) as a fluorescent reporter for imaging of intracellular Ca²⁺, based on the inner-filter-mediated luminescence which was assisted by a Ca²⁺ chelator alizarin red S (ARS). BQDs were prepared by hydrothermal heating of capsicum. The absorption of ARS overlaps with the excitation of the BQDs, the fluorescence of BQDs being quenched through the inner-filter effect. But the absorption of Ca-ARS complex red shifts and shows a poor inner-filter effect. Thus, Ca²⁺ can be detected by the inner-filter-mediated luminescence using the BQDs-ARS nanohybrid system. Using the proposed nanosystem, the imaging of intracellular Ca²⁺ and real-time monitoring of the Ca²⁺ level change under histamine stimulation were also achieved. Thus, this nanosystem holds potential applications in other Ca²⁺-related signal transduction study.