Iron specificity of a biosensor based on fluorescent pyoverdin immobilized in sol-gel glass

Many medical diagnoses, research studies, and industrial processes could benefit from an economical, rapid, sensitive iron biosensor because of the widespread importance of iron, even at ppb levels. Current techniques for measuring iron may be very accurate [1] but can be very expensive, may involve large pieces of equipment, and the procedures can be time-consuming. Colorimetric methods (using ferrozine or 1,10-phenanthroline) with a spectrophotometer are only specific for ferrous iron, and are generally less accurate than methods such as atomic absorption and plasma emission spectroscopy (which measure total iron). Ion-selective electrodes for iron are not commercially available.Various metal binding ligands and techniques have been proposed for the determination of iron. These include: iron sensors based on 1,10-phenanthroline entrapped in sol-gel glass [2,3] ; various fluorescent probes used to detect iron in biological systems [4] ; and ferric ion biosensors using fluorescent siderophores such as azotobactin δ [5], parabactin [6], and pyoverdin [7-10] .Pyoverdin (also called pyoverdine or pseudobactin) is an extracellular fluorescent siderophore produced by some Pseudomonas bacteria growing in low iron environments. There are more than 60 different pyoverdin molecules identified to date, and they all consist of a dihydroxyquinoline chromophore attached to a variable peptide chain (6 to 12 amino acids, of L- and D-form) and a variable side chain [11]. Pyoverdin has potential as an iron biosensor because the fluorescence is quenched by the binding to ferric ion [7].Previously, pyoverdin from P. fluorescens was immobilized on controlled pore glass to produce a biosensor for ferric ion [7] and a biosensor for ferric ion and total inorganic iron [9]. Also, a ferric ion biosensor was developed by immobilizing pyoverdin (from P. fluorescens) in sol-gel glass [8]. In these three iron biosensors based on pyoverdin, the interference due to ferrous ion (Fe2+) and other me