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Fluorescent pH sensors with negligible sensitivity to ionic strength
Bernhard M Weidgans1, Christian Krause, Ingo Klimant
1Institute of Analytical Chemistry, Chemo- and Biosensors, University of Regensburg, D-93040 Regensburg, Germany. otto.wolfbeis@chemie.uni-regensburg.de
The Analyst
|June 24, 2004
Summary
New optical pH sensors use novel lipophilic fluorescein dyes embedded in hydrogels. These sensors minimize ionic strength interference, offering accurate pH determination across a wide range.
Area of Science:
- Analytical Chemistry
- Materials Science
Background:
- Optical pH determination is hindered by ionic strength-dependent signals.
- This signal interference arises from the complex interplay between proton activity, dye concentration, and indicator charge within the immobilization matrix.
Purpose of the Study:
- To develop novel optical pH sensors with negligible ionic strength cross-sensitivity.
- To create sensors utilizing lipophilic fluorescein esters embedded in a proton-permeable hydrogel matrix.
Main Methods:
- Synthesized novel lipophilic fluorescein esters with a single negative charge.
- Embedded these dyes within an uncharged, highly proton-permeable hydrogel.
- Modified dye substituents to achieve a range of dissociation constants.
Main Results:
- Developed optical pH sensors exhibiting negligible cross-sensitivity to ionic strength.
- Achieved dissociation constants for the indicators ranging from pH 5.5 to 8.5.
- Demonstrated a broad dynamic pH range of 4.5 to 8 by combining two indicators in a single sensor.
Conclusions:
- The novel lipophilic fluorescein-based optical pH sensors overcome the limitation of ionic strength dependency.
- These sensors offer a robust and accurate method for pH determination in various sample matrices.
- The ability to combine indicators allows for tunable, extended dynamic ranges in optical pH sensing.