Nitrate-selective optical sensor applying a lipophilic fluorescent potential-sensitive dye

An optical sensor has been developed for continuous determination of nitrat e that is based on a polymer-stabilized emulsion system consisting of a hyd rogel with entrapped plasticizer droplets. The droplets contain a cationic potential-sensitive fluorescent dye (PSD) located near its surface. The cat ionic PSD also acts as an anion-exchange catalyst that extracts nitrate out of the aqueous solution to form a complex (PSD+/NO3-) that moves into the plasticizer droplet due to its lipophilicity. This process causes a decreas e of micro-polarity near the dye, resulting in an increase in the fluoresce nce intensity of the PSD. In a second detection scheme, the fluorescence in tensity information of the PSD is converted into a fluorescence phase shift by mixing into the membrane particles that contain an inert long-lifetime reference luminophore. The second sensing scheme is referred to as "dual li fetime referencing". Both schemes can be used for reversible sensing of nit rate in the 0.1-50 mM range, with response times in the order of 3 min. (C) 2001 Elsevier Science B.V. All rights reserved.