Our technology is based on the proprietary fluorophore silicon rhodamine (SiR). SiR is a bright and photostable rhodamine-like dye. Its key features are its cell permeability, fluorogenic character and compatibility with super-resolution microscopy The fluorescence excitation and emission of SiR are in the far-red, reducing phototoxicity in live-cell imaging experiments. SiR is compatible with most microscopes as it can be used with standard Cy5 settings. The combination of all these properties set SiR-based probes apart from other fluorescent probes. Read more in this Nature Chemistry paper about the properties of SiR.

Fluorogenic probes for live-cell imaging of the cytoskeleton
Our first two products are SiR-actin and SiR-tubulin, two powerful fluorescent probes for live-cell imaging of the cytoskeleton. SiR-actin and SiR-tubulin were recently introduced in a landmark paper published in Nature Methods. The probes combine minimal cytotoxicity with excellent brightness for fluorescence imaging of actin and tubulin. Combined with super-resolution microscopy, SiR-actin and SiR-tubulin permit live-cell imaging of the cytoskeleton with unprecedented resolution.
SiR-actin and SiR-tubulin can be used without transfection and without washing steps. An experiment that highlights these features is the use of SiR-actin to stain the actin fibers of erythrocytes by simply adding SiR-actin to whole blood. Furthermore, their far-red excitation and emission spectra make them compatible with genetically encoded reporters.

Create your own SiR-based probes
SiR derivatives exist in equilibrium between a non-fluorescent spirolactone (“OFF” state) and a fluorescent zwitterion (“ON” state). Aggregation of SiR derivatives favors the “OFF” state, whereas their interaction with polar protein surfaces switches the fluorophore into the “ON” state. Therefore, SiR-based probes are fluorogenic and become fluorescent only when binding to their cellular target. By coupling different ligands to SiR, for example using our NHS ester or by starting from the free acid, you can now create your own powerful probes. More information on the required properties of the ligand can be found here. Our chemists are happy to help you to convert your ligand into a fluorogenic probe; please contact us for further discussions!


  1. Fluorogenic probes for live-cell imaging of the cytoskeleton, G. Lukinavičius et al., Nature Methods, 11, 731–733 (2014)
  2. A near-infrared fluorophore for live-cell super-resolution microscopy of cellular proteins G. Lukinavičius et al., Nature Chemistry, 5, 132–139 (2013).
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