Optical pH Detection with U-Shaped Fiber-Optic Probes and Absorption Transducers

Jakub Zajíc,Vlastimil Matějec,Marie Pospíšilová,Lenka Traplová,Ivo Bartoň

doi:10.1155/2015/513621

Abstract

In medicine knowledge of pH values can provide us with information not only about the patients’ status but also about physiological processes in the patient’s body. Measurements of pH in small-sample volumes and online pH monitoring in vivo can be employed to obtain such information. For such measurements we have developed and investigated U-shaped fiber-optic probes with immobilized pH indicators in this paper. U-shaped probes with a diameter of about 2 mm were prepared. Three different pH indicators, methyl red, methyl orange, and bromothymol blue, were immobilized in two types of matrices, namely, porous silica (PS) and ethylcellulose (EC), and applied on the U-shaped probes. Changes in spectra of transmitted power were measured and calibration curves were determined from these spectra. It has been found that a working pH range of prepared probes was from 3.1 to 7.6. The maximum sensitivity was about 0.1 1/pH unit. Effects of structural relaxations of detection layers and indicator leaching observed in experiments are discussed.

Highlights

Measurements of pH are broadly employed in industry, agriculture, biology, or medicine
This paper presents results of the investigation of Ushaped probes provided with three different absorption pH indicators, namely, methyl orange, methyl red, and bromothymol blue
Experimental results determined with a U-shape probe coated with the layer of methyl red in porous silica are shown in Figures 6(a) and 6(b)

Summary

Introduction

Measurements of pH are broadly employed in industry, agriculture, biology, or medicine. Fiber-optic pH sensors are usually based on the evanescent-wave and reflection principles [4, 8,9,10,11]. Reflection-based sensors have been commercialized [4] Such sensors have been used in medicine [11], for example, for monitoring gastroesophageal reflux, because they are small and can be inserted into medical catheters. Several approaches have been tested in order to increase the response of evanescent-wave fiber-optic pH sensing probes [12,13,14]. This paper presents results of the investigation of Ushaped probes provided with three different absorption pH indicators, namely, methyl orange, methyl red, and bromothymol blue. Spectral responses and calibration curves of the probes are reported

Experiment

Results and Discussion

Bromothymol blue Sorensen buffer

Conclusions