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Investigation of porous glass-like substrates for use in fibre-optic chemical sensors

Badini, G E. (1995). Investigation of porous glass-like substrates for use in fibre-optic chemical sensors. (Unpublished Doctoral thesis, City, University of London)


Fibre optic chemical sensors (FOCSs) are reviewed and a general scheme of a typical sensor is given with details of the various component sections. The interest in FOCSs is presented from the stand-point of the potential advantages which they can offer, but reasons are also proffered for the hitherto small presence of these instruments in the market place. The subject is further developed by considering the types of optical sensors which have been described in the literature. Attention is focussed on the types of sensing materials which have been investigated with particular reference to pH sensing.

A description is given of two opto-electronic configurations which were developed specifically for this investigation. The first consists of a fibre-optic link to a commercial spectrophotometer. The second involved the use of an argon ion laser and was constructed to illustrate some of the other design principles which feature in FOCS. The arrangement of fibres in a simple fibre optic bundle is considered and its optimum configuration is illustrated by experiment.

A data acquisition program which was designed specifically for this work is outlined and, in practice, the use of this program greatly facilitated the acquisition and evaluation of data from the opto-electronic configurations described.

The fluorophore fluorescein isothiocyanate (FITC) is discussed and its fluorescence properties are assessed. The suitability of FITC as a pH sensitive reagent is confirmed using the opto-electronic configurations developed for this study.

The use of porous glass (PG) as a support for the analyte-sensitive reagent in FOCS is investigated in order to gain further understanding regarding the advantages and disadvantages of the use of PG for such applications. Microanalysis was used in an attempt to assess the effect of certain reaction parameters on the efficiency of each of the two steps involved in immobilising FITC onto the glass surface. The low organic content of the derivatised samples limits the overall usefulness of this analytical approach Nevertheless, a model is presented which, with some modification, can explain most of the observations concerning the two step immobilisation reaction involving 3-aminopropyltriethoxysilane (3APTSJ and FITC.

It is found that refluxing in 3APTS in the first step significantly improves the loading of the fluorophore on the porous glass, but that the type of porous glass pretreatment and the concentration of the FITC solution do not result in differences which can be measured by conventional microanalysis.

The fluorescence response of the derivative porous glass, both dry and in solution, was recorded. The fibre optic configuration described resulted in strong fluorescent signals but a longer than desirable response time. Generally, it was found that the fluorescence intensity of the dry PG was greater when lower concentrations of FITC had been used in the immobilisation step.

The sol-gel process is introduced and its potential applicability to preparing glass-like structures which can be used in FOCS is reviewed and further explored.

The main features of sol-gel processing which are potentially relevant to the preparation of a high surface area solid support for use as a sensor substrate are presented. From the literature reviewed it was not possible clearly to define an ideal sol composition which would lead to a material with properties that could best be tailored to FOCS. Nevertheless, there was much evidence that such a material could be prepared and work was conducted in order to investigate this approach with a view of the possible application of such materials in FOCS.

FITC containing monoliths were prepared by two routes; impregnation of the FITC into already formed gels and the incorporation of FITC into the gel at the sol stage. The properties of these materials are discussed with respect to the applicability in FOCS and their stability, both from the point of view of a wet-dry-wet cycle and in terms of storage stability over a number of years.

The preparation of FITC containing coatings is also discussed and appears to offer the best opportunity for use of this technology in FOCS.

Publication Type: Thesis (Doctoral)
Subjects: T Technology > TK Electrical engineering. Electronics Nuclear engineering
Departments: School of Science & Technology > Engineering > Electrical & Electronic Engineering
School of Science & Technology > School of Science & Technology Doctoral Theses
Doctoral Theses
[thumbnail of Badini thesis 1995 PDF-A.pdf]
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