Optochemical sensing by immobilizing fluorophore-encapsulating liposomes in sol-gel thin films

The chemical stability of optochemical sensors depends largely on the physi ochemical properties of the supportive matrix of the sensor and on the meth od used to immobilize sensing reagents to the supportive matrix of the sens or. Leaking of physically immobilized sensing reagents from the matrix supp ort decreases the stability of the sensor and its overall usefulness. Coval ent immobilization eliminates leakage of the sensing reagent from the suppo rt but may lead to alteration of spectral properties and loss of analyte re sponse. This paper presents a new method for physical immobilization of pol ar fluorescence dyes in a sensing support. The method is based on the immob ilization of fluorescent dye encapsulating liposomes in a sol-gel film of m icrometer thickness. The encapsulation of the dye molecules in the liposome s effectively increases the molecular dimensions of the sensing reagent, th us preventing its leakage from the matrix support. This paper describes the analytical properties of a pH sensor fabricated by immobilizing carboxyflu orescein-encapsulating liposomes in a sol-gel thin film. The sensor shows e xcellent stability with respect to dye leaking which in turn leads to high reproducibility and sensitivity of about 0.01 pH units. The linear dynamic range of the sensor is between pH 6 and 7.5 and its response time is at the sub-seconds time scale. (C) 1999 Elsevier Science B.V. All rights reserved .