High-resolution Imaging of pH in Alkaline Sediments and Water Based on a New Rapid Response Fluorescent Planar Optode

Abstract

A new dual-lumophore optical sensor combined with a robust RGB referencing method was developed for two-dimensional (2D) pH imaging in alkaline sediments and water. The pH sensor film consisted of a proton-permeable polymer (PVC) in which two dyes with different pH sensitivities and emission colors: (1) chloro phenyl imino propenyl aniline (CPIPA) and (2) the coumarin dye Macrolex® fluorescence yellow 10 GN (MFY-10 GN) were entrapped. Calibration experiments revealed the typical sigmoid function and temperature dependencies. This sensor featured high sensitivity and fast response over the alkaline working ranges from pH 7.5 to pH 10.5. Cross-sensitivity towards ionic strength (IS) was found to be negligible for freshwater when IS <0.1 M. The sensor had a spatial resolution of approximately 22 μm and aresponse time of <120 s when going from pH 7.0 to 9.0. The feasibility of the sensor was demonstrated using the pH microelectrode. An example of pH image obtained in the natrual freshwater sediment and water associated with the photosynthesis of Vallisneria spiral species was also presented, suggesting that the sensor held great promise for the field applications.

Background-Free Fluorescence-Decay-Time Sensing and Imaging of pH with Highly Photostable Diazaoxotriangulenium Dyes

“…Clearly, because of the self-referenced character of the decay time, the new materials are very promising for lifetime-based micro- and macroscopic imaging using a FLIM technique. pH imaging with planar optodes is important in marine biology, , soil and plant research, , medicine, and other areas, and it is currently performed either in ratiometric mode or using a so-called dual-lifetime-referencing technique. These methods typically require the addition of other luminescent reference emitters, which makes the systems more complex and does not eliminate some interferences (e.g., from light scattering or background fluorescence).…”

Optical Sensing and Imaging of pH Values: Spectroscopies, Materials, and Applications

“…Specially designed software and hardware (now commercially available) makes it possible to control the illumination with photodiodes and to use virtually any consumer RGB camera for imaging. Han et al 991 report on a ratiometric optode for imaging slightly alkaline sediments. It is making use of an indicator immobilized in PVC (p K a ´ of 9.0 at 15 °C).…”

“…Several reported systems utilize a consumer camera, a high power LED for excitation and a trigger to ensure illumination of the sensor foil only during the image acquisition time. Planar optodes have been used for imaging of pH values in marine sediments (Figure B), , seawater, wounded tissues, and for visualization of bacterial metabolism in Petri dishes. , A commercial VisiSens system is available from PreSens GmbH and includes an RGB camera and a set of planar optodes (pH, oxygen, and carbon dioxide). Application of this system for imaging of pH gradients (also pO 2 and pCO 2 gradients) in rhizosphere was demonstrated …”

Noise versus Resolution in Optical Chemical Imaging─How Reliable Are Our Measurements?

“…While the latter one is a self-referenced method that is less susceptible to optical interferences than intensity-based imaging techniques, it requires, however, a more complex and sophisticated detection system. In recent years, optical chemical imaging has advanced tremendously, particularly since it became possible to image analyte distributions using simple and affordable color cameras. ,, Since then, optodes have proven to be valuable tools for various biological, environmental, and medical applications, especially when it comes to the mapping of analyte distributions and dynamics in heterogeneous and complex samples at the microscale − or across scales. − …”