The chromogenic sensing of ions through synthetic chemoreceptors is gaining momentum in view of their crucial roles in our lives. So far there are only a few reports on the chromogenic sensing of Ni²⁺.

Rakesh K. Mishra and K. K. Upadhyay, Banaras Hindu University, Varanasi, India, synthesized the receptor R1 which gave a visible response to Ni²⁺ at the sub-micromolar level at physiological pH in aqueous ethanolic medium. The receptor is the first example of a coumarin-based chromogenic receptor exhibiting a reconfigurable logic gate pattern.

• Coumarin-Based Chromogenic Receptor for Ni²⁺ in Aqueous Medium Exhibiting a Reconfigurable Logic Gate Pattern,
  Rakesh K. Mishra and K. K. Upadhyay,
  Eur. J. Org. Chem. 2011.
  DOI: 10.1002/ejoc.201100511