Issue 7, 2004
From the journal:

Analyst

Fluorescent pH sensors with negligible sensitivity to ionic strength

Bernhard M. Weidgans,a   Christian Krause,b   Ingo Klimantc  and  Otto S. Wolfbeis*a  

* Corresponding authors

a Institute of Analytical Chemistry, Chemo- and Biosensors, University of Regensburg, D-93040 Regensburg, Germany
E-mail: otto.wolfbeis@chemie.uni-regensburg.de
Fax: +49 (0)941 943 4064
Tel: +49 (0)941 943 4066

b PreSens GmbH, Josef-Engert-Str. 9, D-93053 Regensburg, Germany
E-mail: christian.krause@presens.de
Fax: +49 (0)941 942 7227
Tel: +49 (0)941 942 720

c Institute of Analytical Chemistry, Micro- and Radiochemistry, University of Technology, A-8010 Graz, Austria
E-mail: klimant@analytchem.tu-graz.ac.at
Fax: +43 (0)316 873 4328
Tel: +43 (0)316 873 4328

Abstract

Optical pH determination has the fundamental disadvantage of measuring a signal that depends on the ionic strength of the sample. The problem originates from the complex relationship between the proton activity and the concentration of the pH-sensitive dye. The effect of ionic strength on the signal depends on the charge of the indicator and its environment, e.g. the immobilisation matrix. We present novel lipophilic fluorescein esters carrying one negative charge. They are embedded in an uncharged, highly proton-permeable hydrogel to give optical pH sensors that show a negligible cross-sensitivity towards ionic strength. The fluorescent dyes differ in their substituents. This variation of substituents results in dissociation constants between 5.5 and 8.5. The indicators were made lipophilic by esterification of the carboxy group with a C18 alkyl chain. Since their spectral properties are quite similar, two indicators may be used in one sensor. This results in an optical pH sensor with a dynamic range that extends from pH 4.5 to 8.

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Article information

DOI
https://doi.org/10.1039/B404098H
Article type
Paper
Submitted
18 Mar 2004
Accepted
30 Apr 2004
First published
07 Jun 2004

Analyst, 2004,129, 645-650

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Fluorescent pH sensors with negligible sensitivity to ionic strength

B. M. Weidgans, C. Krause, I. Klimant and O. S. Wolfbeis, Analyst, 2004, 129, 645 DOI: 10.1039/B404098H

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