In Vivo Calcium Imaging in the Near-Infrared II Window

Abstract Non-invasive deep-tissue calcium imaging of live mammals with high sensitivity and resolution is challenging owing to light scattering experienced by traditional calcium ion (Ca 2+ ) indicators with excitation and emission wavelengths within 400-750 nm. Here, we report near-infrared II (NIR-II) calcium imaging beyond 1000 nm by exploring a natural protein derived from a bacterium ( Thermochromatium tepidum ) living in a calcium carbonate-rich environment. This highly photostable fluorescent protein enables NIR-II imaging of intracellular Ca 2+ responses to stimulant drugs in cultured mammalian cells with sensitivity comparable to that of visible Ca 2+ indicators. We achieve in vivo NIR-II imaging of Ca 2+ transients in response to two different tumor treatment strategies in intact tumors with high sensitivity, resolution, and contrast, opening the possibility of non-invasive deep-tissue calcium imaging for assessing treatment efficacy longitudinally. TOC Graphic