Luminescence lifetime imaging of oxygen, pH, and carbon dioxide distribution using optical sensors

We present a modular system for time-resolved two-dimensional luminescence lifetime imaging of planar optical chemical sensors. It is based on a fast, gateable charge-coupled device (CCD) camera without image intensifier and a pulsable light-emitting diode (LED) array as a light source. Software was developed for data acquisition with a maximum of parameter variability and for background suppression. This approach allows the operation of the syst em even under daylight. Optical sensors showing analyte-specific changes of their luminescence decay time were tested and used for sensing pO(2), pCO( 2), pH, and temperature. The luminophores employed are either platinum(II)- porphyrins or ruthenium(II)-polypyridyl completes, contained in polymer fil ms, and can be efficiently excited by blue LEDs. The decay times of the sen sor films vary from 70 mu s far the Pt(II)-porphyrins to several 100 ns for the Ru(II) complexes. In a typical application, 7 mm-diameter spots of the respective optical sensor films were placed at the bottom of the wells of microtiterplates. Thus, every well represents a separate calibration chambe r with an integrated sensor element. Both luminescence intensity-based and time-resolved images of the sensor spots were evaluated and compared. The c ombination of optical sensor technology with time-resolved imaging allows a determination of the distribution of chemical or physical parameters in he terogeneous systems and is therefore a powerful tool for screening and mapp ing applications.