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 system even under daylight. Optical sensors showing analyte-specific changes of their luminescence decay time were tested and used for sensing pO2, pCO2, pH, and temperature. The luminophores employed are either platinum(II)-porphyrins or ruthenium(II)-polypyridyl complexes, contained in polymer films, and can be efficiently excited by blue LEDs. The decay times of the sensor films vary from 70 μs for 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 chamber with an integrated sensor element. Both luminescence intensity-based and time-resolved images of the sensor spots were evaluated and compared. The combination of optical sensor technology with time-resolved imaging allows a determination of the distribution of chemical or physical parameters in heterogeneous systems and is therefore a powerful tool for screening and mapping applications.
The imaging of two-dimensional (2D) solute distributions with planar optodes has become an important tool in biological and medical research. The development of versatile and¯exible imaging systems, that enable both luminescence intensity and lifetime imaging, has generated various applications of planar oxygen optodes. Most of the applied optodes however, were not transparent. They either contained scattering particles in the sensing layer for signal enhancement and/or an optical insulation to separate the signal from ambient light. Since the modular luminescence lifetime imaging system (MOLLI) enables luminescence lifetime imaging, we used transparent planar oxygen optodes to investigate simultaneously the 2D distribution of oxygen and the structure that causes this distribution. This is done by either using the luminescence intensity images or different spectral illumination for structural imaging and the luminescence lifetime images for oxygen distribution imaging.As the distribution of oxygen plays a key role at different spatial scales, we present results from applications of the transparent optodes to various biological systems: (a) to a coral sand sediment sample (macrolens application: resolution of approximately 50 mm per pixel); (b) to a lichen with cyanobacteria as symbionts (endoscope application: resolution of approximately 15±62.5 mm per pixel) and (c) to a foraminifer with diatoms as symbionts (microscope application: resolution of approximately 3.8 mm per pixel). The results demonstrate the performance and some of the limits of the application of transparent optodes. Other possible ®elds of applications that are not restricted to marine environment are discussed. #
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