A sensor membrane has been developed for the determination of copper(II) ions that displays excellent performance due to internal referencing of luminescence intensities. The applied sensing scheme (dual lifetime referencing) makes use of the indicator lucifer yellow (LY) and an inert reference luminophore (a ruthenium complex entrapped in polyacrylonitrile beads). Both are contained in a hydrogel matrix. The copper-dependent fluorescence intensity change of LY can be converted in either a phase shift or time dependent parameter. The sensing membrane is capable of determining copper(II) with an outstanding high selectivity over a dynamic range between 1 and 1000 muM in neutral or weekly acidic conditions. The advantages of the referencing method over intensity based measurements was demonstrated by the measurement of turbid solutions. The scheme was also applied to two-dimensional measurements in the time domain. Sensor integrated microtiterplates were imaged with a CCD camera gated with square pulses in the microsecond range. (C) 2002 Elsevier Science B.V. All rights reserved.