A simple and inexpensive high resolution color ratiometric planar optode imaging approach: application to oxygen and pH sensing

A simple, high resolution colormetric planar optode imaging approach is presented. The approach is simple and inexpensive yet versatile, and can be used to study the two-dimensional distribution and dynamics of a range of analytes. The imaging approach utilizes the inbuilt color filter of standard commercial digital single lens reflex cameras to simultaneously record different colors (red, green, and blue) of luminophore emission light using only one excitation light source. Using the ratio between the intensity of the different colors recorded in a single image analyte concentrations can be calculated. The robustness of the approach is documented by obtaining high resolution data of O-2 and pH distributions in marine sediments using easy synthesizable sensors. The sensors rely on the platinum(II) octaethylporphyrin (PtOEP) and lipophilic 8-Hydroxy-1,3,6-pyrenetrisulfonic acid trisodium (HPTS) salt derivate for O-2 and pH measurements, respectively. The brightness of both indicators is dramatically enhanced by making use of energy transfer from a donor molecule (Macrolex yellow coumarin). Furthermore, the emission from the donor serves as an internal reference for the O-2 sensor. The approach relies on semitransparent sensors, facilitating visual inspection of the sediment behind the sensors during measurements. Software for data acquisition and calibration will be available from the authors, whereas all hardware is available from a range of commercial sources. The total cost of the complete measuring system is approximately $3000 US.