Pure and Applied Chemistry

Abstract: The design principles of fluorescence-based siderophore sensor molecules for detection of heavy transition-metal (HTM) ions are first reviewed. As an example, fluorescein-desferrioxamine (FlDFO), a highly efficient fluorophore molecule combining a specific Fe ion receptor and a fluorescence-sensitive signalling site has been designed, synthesized, and used for dosing with Fe ions. Its response test shows its high selectivity and sensitivity to Fe^III ions and its potential for nanobiosensor design. This work clearly identified that among two FlDFO positional isomers differing by the attachment of DFO at the 5- or 6-position of the bottom benzene ring of Fl, the fluorescence of 6-FlDFO is insensitive to the complexation with Fe ions. This is independent of the linkage used between Fl and DFO. Only 5‑FlDFO could be a highly potential sensor molecule since it has been revealed that in a free state without complexation with Fe ions, this fluoroionophore sensor molecule gave a maximum fluorescent signal. With successive Fe ion complexing, the fluorescence of 5-FlDFO decreased very sensitively and proportionally with ion concentration. The response speed has been evaluated as a function of Fe ion concentration. Responses to other metal ions present in the solution, such as Cu²⁺, Ca²⁺, Ni²⁺, and Al³⁺, and the effect of pH value on the efficiency of the sensor molecules have also been investigated.