Development of a far-red to near-infrared fluorescence probe for calcium ion and its application to multicolor neuronal imaging

J Am Chem Soc. 2011 Sep 14;133(36):14157-9. doi: 10.1021/ja205809h. Epub 2011 Aug 18.


To improve optical imaging of Ca(2+) and to make available a distinct color window for multicolor imaging, we designed and synthesized CaSiR-1, a far-red to near-infrared fluorescence probe for Ca(2+), using Si-rhodamine (SiR) as the fluorophore and the well-known Ca(2+) chelator BAPTA. This wavelength region is advantageous, affording higher tissue penetration, lower background autofluorescence, and lower phototoxicity in comparison with the UV to visible range. CaSiR-1 has a high fluorescence off/on ratio of over 1000. We demonstrate its usefulness for multicolor fluorescence imaging of action potentials (visualized as increases in intracellular Ca(2+)) in brain slices loaded with sulforhodamine 101 (red color; specific for astrocytes) that were prepared from transgenic mice in which some neurons expressed green fluorescent protein.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Calcium / analysis*
  • Cations, Divalent / analysis
  • Fluorescent Dyes / chemistry*
  • Hippocampus / chemistry*
  • Hippocampus / cytology
  • Mice
  • Neurons / chemistry*
  • Rhodamines / chemistry*
  • Spectrometry, Fluorescence / methods*
  • Spectroscopy, Near-Infrared / methods*


  • Cations, Divalent
  • Fluorescent Dyes
  • Rhodamines
  • Calcium