Stability of pyrene-1-carboxylic acid and other pyrene derivatives immobilized on silane gels

The main aim of this research was to select a silane gel with appropriate composition containing fluorophore immobilized in it, in view of application of this carrier in the construction of a fluorescence optical sensor. Results of stationary fluorescence studies on gelation of silane gel with different composition, obtained as a result of acidic or basic hydrolysis using the fluorophores: pyrene-1-carboxylic acid and 1,3-bis(1-pyrenyl)propane, are presented. The form of probe during sol–gel transition and in the formed gel is discussed. The presence of a protonated form of PyCOOH 2 + was observed in the gel obtained by acidic hydrolysis and of PyCOO − ions and neutral form of PyCOOH in the gel obtained with the use of basic hydrolysis. The aim of the research was also to estimate suitability of the silane gel, which contained a selected immobilized fluorophore, for application in the optical sensor. This criterion includes determination of the kinetics of fluorophore elution from the gel as well as estimation of the interactions of fluorophore immobilized in the gel with microenvironment. Therefore, to carry out this part of the research, the silane gel was formed into a thin layer deposited on a glass surface. Next, the kinetics of elution of pyrene-1-carboxylic acid, 1,3-bis(1-pyrenyl)propane as well as pyrene and aminopyrene from this layers by water and ethanol was investigated. Elution rate constants were determined with the use of the first-order kinetics. Three stages of the elution with different duration were distinguished: I 0–4 min, II 4 min–1 h and III, the slowest one—above 1 h. Stability of the probes immobilized in these gels during storage in water or ethanol for several days was also determined.