Submicron sensors for ion detection based on measurement of luminescence decay time

Submicron optochemical sensors for pH and chloride were developed by coatin g silanised optical fibre tips of similar to 300 nm diameter and aluminium- coated SNOM fibres of similar to 50 nm aperture with polymeric membranes co ntaining luminescent indicators. Luminescence decay time was measured using a phase-modulation technique. Changes in decay time are induced by resonan ce energy transfer from a ruthenium complex (the donor) to the pH indicator bromothymol blue (the acceptor). The donor-acceptor ion pair was immobilis ed in a hydrogel membrane and undergoes a change in decay time with pH. The chloride sensor was made by combining the ion pair for optical transductio n with the chloride-carrier tridodecylmethylammonium chloride in a plastici sed PVC membrane. Chloride ions present in the solution are carried into th e membrane. In order to maintain electroneutrality, an equivalent molar qua ntity of protons is coextracted into the membrane where the dye is protonat ed. Both sensors are suitable for measurements in physiological fluids. (C) 2001 Elsevier Science B.V. All rights reserved.