Copper calcein

A fluorimetric FIA system based on the fluorescence enhanced effect of cyanide on the copper- bis[N,N-bis-(carboxymethyl)aminomethyl]fluorescein (calcein) complex has been used for cyanide determination [34]. Also, a flow-through sensing approach was developed based on the immobilization of the calcein on a nonionic resin. Both systems are based on the interaction between the nonfluorescent copper-calcein complex and cyanide. Interaction of cyanide with the Cu(II) ions boimd to calcein resulted in the restoration of the calcein fluorescence. Linear dynamic range from the quantification limit is up to 0.4 mM CN , detection limit 4 x 10 mM CN, relative standard deviation 1.2%, and sampling frequency is 30 Hz h in the FIA system. For the flow-through approach, the linear dynamic range from the quantification limit was up to 0.2 mM CN, the detection limit 5 X 10 mM CN, the relative standard deviation 3.7%, and the sampling frequency is 10 Hz hr ... 

By introducing the complexing moiety —CH2N(CH2C02H)2 into fluorescein or umbelliferone metallochromic indicators termed calcein or fluorexone, and calcein blue or umbellicomplexone are formed. These indicators exhibit green (and blue) fluorescence in dilute alkali which disappears at pH 12 but reappears on the addition of calcium, strontium, or barium. Problems arise from the difficulty of freeing the indicators from fluorescent impurities, from self-fluorescence, and from the quenching effect of copper ions. 

A particularly elegant solution for the assay of proteases and acylases is offered by the fluorogenic detection of free amino acids by decomplexation of copper from calcein, which removes its quenching effect This principle has been used for assays of acylases, amidases, and proteases (Scheme 1.13) [52, 53]. For the case of proteases combinatorial assays are particularly in demand for testing multiple peptides in parallel and determining the cleavage specificity [54]. New solutions... 

Gholivand, M. B. Sohrabi, A. Abbasi, S. Determination of copper by adsorptive stripping voltammetry in the presence of calcein blue. Electroanalysis 2007, 19, 1609-1615. 

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