Luminescence lifetime imaging with transparent oxygen optodes

The imaging of two-dimensional (2D) solute distributions with planar optode s has become an important tool in biological and medical research. The deve lopment of versatile and flexible imaging systems, that enable both lumines cence intensity and lifetime imaging, has generated various applications of planar oxygen optodes. Most of the applied optodes however, were not trans parent. They either contained scattering particles in the sensing layer for signal enhancement and/or an optical insulation to separate the signal fro m ambient light. Since the modular luminescence lifetime imaging system (MO LLI) enables luminescence lifetime imaging, we used transparent planar oxyg en optodes to investigate simultaneously the 2D distribution of oxygen and the structure that causes this distribution. This is done by either using t he luminescence intensity images or different spectral illumination for str uctural imaging and the luminescence lifetime images for oxygen distributio n 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 applica tion: resolution of approximately 50 mum per pixel); (b) to a lichen with c yanobacteria as symbionts (endoscope application: resolution of approximate ly 15-62.5 mum per pixel) and (c) to a foraminifer with diatoms as symbiont s (microscope application: resolution of approximately 3.8 mum per pixel). The results demonstrate the performance and some of the limits of the appli cation of transparent optodes. Other possible fields of applications that a re not restricted to marine environment are discussed. (C) 2001 Elsevier Sc ience B.V. All rights reserved.