Luminescence lifetime imaging with transparent oxygen optodes

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 flexible 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 mum per pixel); (b) to a lichen with cyanobacteria as symbionts (endoscope application: resolution of approximately 15-62.5 mum per pixel) and (c) to a foraminifer with diatoms as symbionts (microscope application: resolution of approximately 3.8 mum per pixel). The results demonstrate the performance and some of the limits of the application of transparent optodes. Other possible fields of applications that are not restricted to marine environment are discussed. (C) 2001 Elsevier Science B.V. All rights reserved.