Existing biarsenical probes have been used in imaging, biophysical fluorescence studies, fluorophore-assisted light inactivation, and for protein and protein complex isolation. In addition to the original probes, FlAsH and ReAsH, improved dyes with better properties have recently been synthesized.

However, to date all biarsenical probes have the same distance (approximately 6 Angstroms) between the two arsenic moieties, and therefore have optimal binding to the same Tetracoordinate Arsenic Grasp (TAG) motifs (CysCysXXCysCys).

Researchers at PNNL have reported a new Cy3-based biarsenical probe, Ascy3, which binds to the Cy3TAG (CysCysLysAlaGluAlaAlaCysCys). This new Cy3TAG is highly selective in binding Ascy3 over FlAsH. In binding experiments between FlAsH-labeled calmodulin (CaMFlAsHTAG) and a myosin light chain kinase-derived CaM-binding peptide (M13 peptide) containing the Cy3-TAG, it has been shown that Ascy3 is a FRET partner to FlAsH, providing a second binding probe with its own TAG for FRET (Fluorescence Resonance Energy Transfer) measurements. The new probe also displays high brightness and photo-bleaching resistance. The distance between two arsenics is about 14.5 Angstrom.