ClopHensor is a ratiometric, non-FRET based biosensor that can be used to measure changes in Cl[-] and intracellular pH simultaneously. It consists of the E[2]GFP and monomeric DsRed fluorescent proteins fused via a flexible 20 amino acid linker. E[2]GFP was derived from EGFP, by introducing the T203Y amino acid substitution, which results in a Cl[-] binding site; binding of Cl[-] to E[2]GFP induces static quenching of its fluorescence. Monomeric DsRed is insensitive to both pH and Cl[-] ion concentration (PMID:20581829).