Using Native Chemical Ligation for Site‐Specific Synthesis of Hetero‐bis‐lanthanide Peptide Conjugates: Application to Ratiometric Visible or Near‐Infrared Detection of Zn2

The interest in ratiometric luminescent probes that detect and quantify a specific analyte is growing. Owing to their special luminescence properties, lanthanide(III) cations offer attractive opportunities for the design of dual‐color ratiometric probes. Here, the design principle of hetero‐bis‐lanthanide peptide conjugates by using native chemical ligation is described for perfect control of the localization of each lanthanide cation within the molecule. Two zinc‐responsive probes, r‐LZF1Tb|Cs124|Eu and r‐LZF1Eu|Cs124|Tb are described on the basis of a zinc finger peptide and two DOTA (DOTA=1,4,7,10‐tetraaza‐cyclododecane‐1,4,7,10‐tetraacetic acid) complexes of terbium and europium. Both display dual‐color ratiometric emission in response to the presence of Zn2+. By using a screening approach, anthracene was identified for the sensitization of the luminescence of two near‐infrared‐emitting lanthanides, Yb3+ and Nd3+. Thus, two novel zinc‐responsive hetero‐bis‐lanthanide probes, r‐LZF3Yb|Anthra|Nd and r‐LZF3Nd|Anthra|Yb were assembled, the former offering a neat ratiometric response to Zn2+ with emission in the near‐infrared around 1000 nm, which is unprecedented. Two are better than one: Site‐specific decoration of a zinc finger peptide with two distinct lanthanide(III) cations affords luminescent probes emitting in the visible or the near‐infrared for dual‐color ratiometric detection of Zn2+. This illustrates a general strategy relying on native chemical ligation for the site‐specific anchoring of two distinct DOTA‐lanthanide(III) (DOTA=1,4,7,10‐tetraaza‐cyclododecane‐1,4,7,10‐tetraacetic acid) onto a peptide to access ratiometric probes.