Platinum octaetylporphyrin based planar optodes combined with an UV-LED excitation light source: An ideal tool for high-resolution O-2 imaging in O-2 depleted environments

A planar optode system based on an O-2 quenchable luminophore platinum(II) 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin (PtOEP) and UV-light emitting diodes (LEDs) was developed and tested for high precision measurements in O-2 depleted aquatic environments. The luminescence lifetime (T) of the PtOEP optode changed from 85.7 to 26.7 mu sec as seawater changed from anoxic to an O-2 concentration of 219 mu M (100% air-saturation at S=35.0, 23.0 degrees C). The dynamic range was up to 18 times higher than a parallel optode measurements performed by conventional ruthenium complexes and blue LED's (depending on the O-2 concentration). The sensitivity of the PtOEP planar optodes remained unchanged even after 19 h of continuous UV radiation at intensity comparable to that of standard measuring conditions. The prototype of a newly developed, multi-gateable CCD camera with a 14 bit AID converter was used for imaging at a 14 bit digital resolution using a CCD-chip of 1344 x 1024 pixels. The calibrated signal correlated well to that of simultaneously obtained microelectrode measurements (R-2=0.999) and the image accuracy (pixel-to-pixel variation) at anoxia and at 175 mu M (80% air-saturation) was +/- 0.4 and +/- 7.0 mu M, respectively. Pixel-to-pixel calibration of acquired images combined with image averaging and moderate pixel binning resulted in a very high precision O-2 images. Laboratory measurements in small flume aquaria documented that PtOEP based optodes combined with UV excitation was an attractive alternative to other established planar optode systems for measurements in O-2 depleted environments. The described system was used for detailed investigations along the anoxic isoline of an intertidal sediment and continuous O-2 imaging revealed previously unresolved microscale O-2 dynamics along this interface. Local O-2 depleted microniches (1.0 x 1.0 mm) appeared and reoxidized within minutes. The dynamics were induced by meiofauna activity and the observation can have important implications for early diagenesis in marine sediments. (c) 2005 Elsevier B.V. All rights reserved.