Solid surface photoluminescence and flow analysis: a happy marriage

Abstract

A specially active field of scientific research in photoluminescence nowadays is its use to study microheterogeneous systems and, conversely, to investigate how the emission properties of a lumiphor can be improved by manipulating the physico-chemical properties of its microenvironment. Applications of such basic chemical knowledge to improve analytical detection, particularly in flowing systems, is arousing a great deal of interest. A major breaktrough in this vein was the use of “organized media” to improve luminescence quantum yields in solution. An alternative to the use of “ordered media” to further enhance the rigidity of the lumiphor is by adsorbing or binding it to a solid matrix, as in solid surface luminescence (SSL). Unfortunately SSL is a rather discoutinuous technique and so less suited than fluid “organized media” for detection in a flow system. An elegant way-out to such a limitation is the coupling (marriage) of SSL with FIA techniques. Solid surface photoluminescence and flow analysis have had a most fortunate encounter, as the merging of the two techniques is providing new avenues for optical sensor transduction and SSL techniques improvement. Fluorimetric advantages of such combinations for new optical sensor development are dealth with and illustrated with the development of a very sensitive and selective optosensor for low aluminium levels in samples of utmost importance in renal failure disease control. However, the potential advantages and increased scope of SSL–FIA combinations are more fully realised when using room temperature phosphorescence (RTP) detection in an aqueous flow system. It is shown how new possibilities for fundamental and applied studies on the SS-RTP phenomenon are opened. SS-RTP—FIA analytical applications to sensing of cations (e.g., by using ferron reagent to bind the cation and retaining this RTP chelate in a flow-through cell), of anions (e.g., an optically “active” phase with the complex Al8-hydroxyquinoline becomes phosphorescent in the flow-through cell only when iodide is bound to it) or oxygen (which quenches the RTP signal of a phosphorescent “active” phase) which can be analyzed in gas mixtures or dissolved in solutions. Finally, basic measurements carried out in our laboratory will be used to explain the amazingly strong RTP signals obtained in aqueous solutions by using anion-exchange resins to retain the studied phosphors.