The University of Southampton
University of Southampton Institutional Repository

Interrogation of optical pH sensor based on sol-gel doped new luminescent europium chelate with compact photon counting system

Interrogation of optical pH sensor based on sol-gel doped new luminescent europium chelate with compact photon counting system
Interrogation of optical pH sensor based on sol-gel doped new luminescent europium chelate with compact photon counting system
Summary: This paper presents recent measurements of novel Eu3+-complex doped sol gel layers (ref 1) which are intended for use as pH indicators, with interrogation by monitoring their fluorescent decay with a compact photon-counting receiver (ref 2). The basic chemistry is outlined and the instrumental arrangement and experimental results are described.

Requirements and basic concept of indicator chemistry. Luminescent lanthanide chelates have many applications, being useful alternatives to standard fluorescent dyes especially when there is significant autofluorescence. They are also useful donors for use in energy transfer experiments to determine static inter-molecular distances. These applications arise because of the chelates' excellent solubility and unusual spectral characteristics, including narrow (<10 nm) spectral emission, large Stokes shifts (>150 nm), potentially high quantum yields.

Selvin et al. have synthesized several lanthanide chelates but all show inconvenient excitation maxima around 340 nm. In contrast, our novel long-wave luminescent dye, based on europium luminescence initiated by a covalently-bonded antenna fluorophor, shows excitation maxima at 370 nm where low cost LEDs are now available. To design sensors of high stability and long lifetime, the sensor matrix and sensor technology are of prime interest. Sol-gel technology enables the production of proton-permeable glassy layers at room temperature and offers simple methods for manipulation of the basic composition, molecular structure, and hence the chemical characteristics of organic matrices.

Time-resolved fluorometry is preferable to conventional fluorometry, since there are no intensity related problems due to turbid samples, self-filter effect, and cuvette geometry. Also, the fluorescence decay time is usually independent of the concentration of the indicator, even when it has been partially modified by leaching out, by decomposition, or by photo bleaching.

In the current work, the Eu3+-complex has been successfully entrapped into tetramethoxysilane (TMOS)-based sol-gel matrices. It was initially found that a Eu3+-complex, which showed useful pH sensitivity in aqueous solution, lost this sensitivity when immobilized in sol-gel matrices. In order to recover this property, the pH indicator bromothymol blue (BTB) was added to the starting sol-gel components and it was found that the useful pH response that was present in water was not only restored, but was actually improved upon.

Instrumentation and experiment for interrogation of Eu3+-complex-doped sol-gel coated layer. The arrangement shown in fig 1 was used for rapid interrogation of fluorescence lifetime. The arrangement improves signal to noise because the sol-gel coating is illuminated directly with a filtered UV LED source, rather than via an optical fibre probe. This increases illumination intensity by removing optical power loss in the launch optics, illuminates a large coating area, and reduces the background auto-fluorescence signal generated from combined launch and return optics. The main excitation peak occurs at 370 nm, which falls in the absorption band of the pH-sensing layer. It should be noted that this arrangement, which was used to improve signal to noise and reduce self-fluorescence in our measurement, was considered to be only an interim step on the way to developing an all-fibre system for illumination and collection of light. Clearly similar gains in signal can be achieved by using larger input and output fibres or fibre bundles, and self-fluorescence can be reduced by use of separate fibre cables for incident and fluorescent light.

Austin, E.A.
5e62fbb2-313b-4368-a371-2d8cb7978109
Dakin, J.P.
490d5873-c444-423b-8d83-c49f118dc4b5
Lobnik, A.
d0937bfa-93d1-4b23-b77a-399403a8e037
Uray, G.
ee29d2fe-981e-4378-b861-3c10381ef53c
Austin, E.A.
5e62fbb2-313b-4368-a371-2d8cb7978109
Dakin, J.P.
490d5873-c444-423b-8d83-c49f118dc4b5
Lobnik, A.
d0937bfa-93d1-4b23-b77a-399403a8e037
Uray, G.
ee29d2fe-981e-4378-b861-3c10381ef53c

Austin, E.A., Dakin, J.P., Lobnik, A. and Uray, G. (2002) Interrogation of optical pH sensor based on sol-gel doped new luminescent europium chelate with compact photon counting system. Europt(R)ode VI, Manchester, UK. 06 - 09 Apr 2002.

Record type: Conference or Workshop Item (Paper)

Abstract

Summary: This paper presents recent measurements of novel Eu3+-complex doped sol gel layers (ref 1) which are intended for use as pH indicators, with interrogation by monitoring their fluorescent decay with a compact photon-counting receiver (ref 2). The basic chemistry is outlined and the instrumental arrangement and experimental results are described.

Requirements and basic concept of indicator chemistry. Luminescent lanthanide chelates have many applications, being useful alternatives to standard fluorescent dyes especially when there is significant autofluorescence. They are also useful donors for use in energy transfer experiments to determine static inter-molecular distances. These applications arise because of the chelates' excellent solubility and unusual spectral characteristics, including narrow (<10 nm) spectral emission, large Stokes shifts (>150 nm), potentially high quantum yields.

Selvin et al. have synthesized several lanthanide chelates but all show inconvenient excitation maxima around 340 nm. In contrast, our novel long-wave luminescent dye, based on europium luminescence initiated by a covalently-bonded antenna fluorophor, shows excitation maxima at 370 nm where low cost LEDs are now available. To design sensors of high stability and long lifetime, the sensor matrix and sensor technology are of prime interest. Sol-gel technology enables the production of proton-permeable glassy layers at room temperature and offers simple methods for manipulation of the basic composition, molecular structure, and hence the chemical characteristics of organic matrices.

Time-resolved fluorometry is preferable to conventional fluorometry, since there are no intensity related problems due to turbid samples, self-filter effect, and cuvette geometry. Also, the fluorescence decay time is usually independent of the concentration of the indicator, even when it has been partially modified by leaching out, by decomposition, or by photo bleaching.

In the current work, the Eu3+-complex has been successfully entrapped into tetramethoxysilane (TMOS)-based sol-gel matrices. It was initially found that a Eu3+-complex, which showed useful pH sensitivity in aqueous solution, lost this sensitivity when immobilized in sol-gel matrices. In order to recover this property, the pH indicator bromothymol blue (BTB) was added to the starting sol-gel components and it was found that the useful pH response that was present in water was not only restored, but was actually improved upon.

Instrumentation and experiment for interrogation of Eu3+-complex-doped sol-gel coated layer. The arrangement shown in fig 1 was used for rapid interrogation of fluorescence lifetime. The arrangement improves signal to noise because the sol-gel coating is illuminated directly with a filtered UV LED source, rather than via an optical fibre probe. This increases illumination intensity by removing optical power loss in the launch optics, illuminates a large coating area, and reduces the background auto-fluorescence signal generated from combined launch and return optics. The main excitation peak occurs at 370 nm, which falls in the absorption band of the pH-sensing layer. It should be noted that this arrangement, which was used to improve signal to noise and reduce self-fluorescence in our measurement, was considered to be only an interim step on the way to developing an all-fibre system for illumination and collection of light. Clearly similar gains in signal can be achieved by using larger input and output fibres or fibre bundles, and self-fluorescence can be reduced by use of separate fibre cables for incident and fluorescent light.

Text
2352.pdf - Other
Download (132kB)

More information

Published date: 2002
Venue - Dates: Europt(R)ode VI, Manchester, UK, 2002-04-06 - 2002-04-09

Identifiers

Local EPrints ID: 17064
URI: http://eprints.soton.ac.uk/id/eprint/17064
PURE UUID: 12047412-8da2-4be5-bcf1-2fa3256cc9c8

Catalogue record

Date deposited: 13 Sep 2005
Last modified: 22 Jul 2020 16:33

Export record

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of http://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×