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Updated: May 5, 2026

In Vivo 2-Photon Calcium Imaging in Layer 2/3 of Mice
Published on: March 13, 2008
In Vivo Calcium Imaging in the Near-Infrared II Window
Danyang Xu1,2, Zhisheng Wu1, Hui Yang3
1Department of Electrical and Electronic Engineering, The University of Hong Kong, Kowloon, Hong Kong SAR 999077, China.
Abstract:
Noninvasive deep-tissue calcium imaging of live mammals with high sensitivity and resolution is challenging owing to light scattering experienced by traditional calcium ion (Ca2+) 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 Ca2+ responses to stimulant drugs in cultured mammalian cells with sensitivity comparable to that of visible Ca2+ indicators. We achieve in vivo NIR-II imaging of Ca2+ transients in response to two different tumor treatment strategies in intact tumors with high sensitivity, resolution, and contrast, opening the possibility of noninvasive deep-tissue calcium imaging for assessing treatment efficacy longitudinally.
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