WO2012098242A1

WO2012098242A1 - Optical sensor

Info

Publication number: WO2012098242A1
Application number: PCT/EP2012/050900
Authority: WO
Inventors: Hien Nguyen; Tong Sun; Ken GRATTAN; Susan Taylor; Muhammed BASHEER; Adrian Long
Original assignee: City University; Queens University Of Belfast
Priority date: 2011-01-20
Filing date: 2012-01-20
Publication date: 2012-07-26
Also published as: EP2666010A1; GB201100989D0

Abstract

An optical sensor (1) for pH monitoring in highly alkaline mediums, the sensor (1) comprising: a sensor body (3) that fluoresces when illuminated by light, the sensor body (3) being configured to exhibit a change in fluorescence in response to changing pH in highly alkaline mediums, the sensor further comprising means (5) for coupling the sensor body to a source of illumination. A system (11) is also disclosed, along with methods of synthesising pH sensitive polymerisable fluorescent coumarin dyes, and pH sensitive polymerisable fluorescent coumarin dyes.

Description

OPTICAL SENSOR

Field

This invention relates to optical sensors, and systems employing such sensors. In one envisaged implementation, the sensors are configured to be responsive to the pH of a highly alkaline medium to which the sensor is exposed.

In one implementation, the teachings of the invention may be employed to measure the pH in building materials (such as, for example: concrete, cement, mortar (e.g. limestone mortar)), and the following detailed description will refer to this particular application in detail hereafter. It should be remembered, however, that this application is merely illustrative and hence that the teachings of the invention may otherwise be employed without departing from the scope of the invention.

Background

Optical sensors are used in many applications as such sensors tend to be relatively small in size, and relatively resistant to electromagnetic interference and harsh chemical environments.

In the Civil Engineering Sector (where it is not unusual for the ambient environment to which a sensor is exposed to have a pH of over 10, and often 12 or over) such sensors would be particularly well suited as conventional sensors, such as glass electrode devices, are typically too fragile and generally unsuitable for highly alkaline mediums.

It is not surprising, therefore, that companies such as Ocean Optics (see: www.oceanoptics.com) do offer several optical pH sensors for sale. However, the sensors that are currently available tend to be limited to being responsive to pH's of 12 or less, and tend to have a very short lifetime (typically in the order of weeks).

It would be advantageous, therefore, if an optical sensor could be developed that is responsive to pH's of about 10 or above, in particular to pH's of 12 or above, and which has a longer lifetime. One aim of the present invention is to provide just such a sensor. Summary

To this end, a presently preferred embodiment of the present invention provides: an optical sensor for in-situ pH monitoring in highly alkaline mediums (such as may be found in concrete structures, for example, where the pH is at least 10, and often 12 or over), the sensor comprising: a sensor body that fluoresces when illuminated by light, the sensor body being configured to exhibit a change in fluorescence in response to changing pH in highly alkaline mediums. The sensor body may further comprise means for coupling the sensor body to a source of illumination.

In a preferred arrangement, the change in fluorescence comprises a change in fluorescence intensity. For example, the sensor body may exhibit a reduction in fluorescence intensity as the pH of the medium increases.

The fluorescent sensor body may comprise a polymerised coumarin dye that bears an imidazolyl group. The sensor body may comprise polymerised 7-(4-vinylbenzylamino)-4- ((2-methyl-4-nitro-1 /-/-imidazol-1-yl)methyl)-coumarin or polymerised 7-vinylphenyl-4-((2- methyl-4-nitro-1 /-/-imidazol-1-yl)methyl)-coumarin.

The sensor body may comprise a layer of particles.

The optical coupling means may be configured to be optically transparent to a range of wavelengths including that at which the sensor body fluoresces.

The optical coupling means may be of quartz.

The sensor body may be abutted against the optical coupling means.

The sensor body may be configured to fluoresce when illuminated with light having a centre wavelength of about 370 to 380nm, preferably about 375nm.

The sensor body may be sandwiched between said optical coupling means and a permeable cover. The cover may include a plurality of pores, each of about 20 microns in diameter. The cover may be of nylon.

Another aspect of the invention relates to a system for determining pH, the system comprising: an optical sensor as disclosed herein; a lamp; a spectrometer, and means for coupling the lamp to the optical coupling means of the optical sensor, and for coupling the optical coupling means of the sensor to the spectrometer.

The means for coupling the lamp to the optical coupling means of the optical sensor may comprise an optic fibre. The means for coupling the optical coupling means of the optical sensor to the spectrometer may comprise an optic fibre.

The system may comprise a first optic fibre coupling the lamp to the optical sensor, and a second optic fibre coupling optical sensor to the spectrometer.

The system may comprise a fibre coupler for coupling said first and second optic fibres together in a single cable so that light from the lamp is directed via the first optic fibre to illuminate a first part of said sensor body, and so that fluorescence from said first part is directed via said second fibre to said spectrometer.

The system may comprise a computing resource coupled to the spectrometer for the receipt of data therefrom.

Another aspect of the invention relates to a method of synthesising a pH sensitive fluorescent dye polymer, the method comprising the steps of: (a) synthesising a pH sensitive polymerisable coumarin dye that bears an imidazolyl group, and (b) polymerising the dye to provide a pH sensitive fluorescent polymer.

Yet another aspect of the invention relates to a method of synthesising a pH sensitive polymerisable coumarin dye, the method comprising:

(a) reacting 3-aminophenol with ethyl chloroformate in ethyl acetate (EtOAc) to provide 3-/V-(Carbethoxy)aminophenol;

(b) reacting 3-/V-(Carbethoxy)aminophenol with ethyl 4-chloroacetoacetone in sulphuric acid (80%) to provide 4-Chloromethyl-7-/V-(Carbethoxy)aminocoumarin;

(c) hydrolysing 4-Chloromethyl-7-/V-(Carbethoxy)aminocoumarin using a mixture of concentrated sulphuric acid and glacial acetic acid to provide 4-Chloromethyl-7- aminocoumarin;

(d) reacting 4-Chloromethyl-7-aminocoumarin with 2-methyl-4-nitroimidazole in dimetylformamide (DMF), using NaH in mineral oil (60%) as a base to afford 7-amino-4-((2- methyl-4-nitro-1 /-/-imidazol-1-yl)methyl)-coumarin; and

(e) reacting 7-amino-4-((2-methyl-4-nitro-1 /-/-imidazol-1-yl)methyl)-coumarin with vinylbenzylchlonde in acetonitrile in the presence of potassium carbonate and posstasium iodide to provide 7-(4-vinylbenzylamino)-4-((2-methyl-4-nitro-1 /-/-imidazol-1-yl)methyl)- coumarin.

Another aspect of the invention relates to a method of synthesising a pH sensitive polymerisable fluorescent coumarin dye, the method comprising:

(a) reacting 3-bromophenol with ethyl 4-chloroacetoacetone in sulphuric acid (80%) to provide 4-chloromethyl-7-bromocoumarin;

(b) reacting 4-chloromethyl-7-bromocoumarin with 2-methyl-4-nitroimidazole in dimetylformamide (DMF), using NaH in mineral oil (60%) as a base to afford 7-bromo-4-((2- methyl-4-nitro-1 /-/-imidazol-1-yl)methyl)-coumarin; and

(c) reacting 7-bromo-4-((2-methyl-4-nitro-1 /-/-imidazol-1-yl)methyl)-coumarin with 4- vinylphenylboronic acid in dioxane, using tetrakis(triphenylphosphine)palladium(0) as a catalyst and posstasium carbonate as a base to provide 7-vinylphenyl-4-((2-methyl-4-nitro- 1 /-/-imidazol-1-yl)methyl)-coumarin.

A further aspect of the invention relates to a pH sensitive polymerisable coumarin dye of the formula:

Yet another aspect of the invention relates to a pH sensitive polymerisable coumarin dye of the formula:

Other features, aspects and advantages of the teachings of the invention will be apparent from the following detailed description.

Brief Description of the Drawings

Various aspects of the teachings of the present invention, and arrangements embodying those teachings, will hereafter be described by way of illustrative example with reference to the accompanying drawings, in which:

Fig. 1 is a schematic cross-sectional representation of an optical sensor embodying the teachings of the invention;

Fig. 2 is a schematic representation of a sensing system employing the sensor of

Fig. 1 ;

Fig. 3 is a schematic representation of a typical fluorescence spectrum for the sensor of Fig. 1 ;

Figs. 4 is an illustrative calibration curve for sensors of the type depicted in Fig. 1 when immersed in media of increasing pH; and

Figs. 5 and 6 are diagrammatic representations of illustrative methods of producing a polymerisable coumarin dye for use in a sensor of the type shown in Fig. 1 ; Detailed Description

In general terms, the sensor described hereafter employs a sensor body that comprises a dye polymer which fluoresces when illuminated by light of a given wavelength. The sensor body comprises a coumarin dye that bears an imidazolyl group as a fluorescent indicator, and protonation / deprotonation of nitrogen on the imidazolyl group enables the pH of the medium to be determined in the highly alkaline region of the pH scale where the pH is about 10 or higher, and more particularly in regions where the pH is at least 12.

The pH of a given medium can be determined from the intensity of fluorescence according to the following equation:

where F is a measured fluorescence intensity of the system, F_max is the fluorescence intensity of the fully protonated system, F_min is the fluorescence intensity of the deprotonated system, and pKa is the variable fitting parameter - which is the pH where 50% of the dye population in solution is protonated.

Referring now to Fig. 1 of the accompanying drawings, the sensor 1 comprises a sensor body 3 sandwiched between a means 5 (such as a quartz disc (for example of about 6mm in diameter) or other material that is optically transparent at the wavelength ranges of interest) for optically coupling the sensor body 3 to a source of illumination and a permeable cover 7. The optical coupling means/sensor body/cover sandwich is kept together by one or more fasteners, such as an o-ring 9 for example.

The sensor body 3 comprises a layer of dye polymer particles, and the cover 7 functions to keep the dye polymer particles closely coupled to the optical coupling means 5, and to prolong the life of the sensor (in particular to reduce the likelihood of the sensor body being mechanically damaged) whilst allowing hydrogen ions to permeate into the sensor body. In one envisaged arrangement the permeable cover 7 comprises a nylon membrane with pores of about 20 microns in diameter, but numerous other suitable materials will be apparent to persons of ordinary skill in the art. The cover may also be dispensed with if the layer of dye polymer particles are fixed to the optical coupling means 5.

In one implementation the sensor body 3 comprises a relatively small amount, say about 4 mg, of dye polymer provided as a layer of particles between the cover 7 and the optical coupling means 5.

In general terms, the sensor body 3 comprises a coumarin dye that was polymerised together with methacrylic acid and bis(acryloyl)piperazine in the presence of pluronic P84 as surfactant at 80 degrees centigrade in the dark for approximately 20 hours. The resultant hard bulk polymer was then crushed and a layer of the dye polymer was sandwiched between the aforementioned optical coupling means and the cover.

Referring now to Fig. 2, the aforementioned sensor 1 may be employed in a system 1 1 for monitoring pH in a highly alkaline medium that has a pH of at least about 10, such as concrete or other building materials.

In the system 1 1 depicted, the aforementioned sensor 1 has been coupled to a lamp 23 and a spectrometer 25 by first and second optic fibres 19, 21. The first optic fibre 21 is arranged to direct light from the lamp 23 towards the sensor 1 , and the second optic fibre 19 directs light (due to fluorescence in the sensor 1) from the sensor 1 to the spectrometer 25 (note that the optical coupling means of the sensor is not visible in Fig. 2 because the sensor is shown as being mounted in a hollow holder 15 that opens at one end to enable the sensor to be exposed to a medium of interest, and at the other end to allow the holder to be coupled to an optic fibre).

The first and second optic fibres 19, 21 are, in this particular configuration, coupled to a fibre coupler 17, in this instance to a 2x1 Y fibre coupler, which combines the first and second fibres 19, 21 into a single cable 13 (where the first and second fibres are combined together within a single jacket) that is coupled to the aforementioned holder 15. This arrangement is preferred because a region of the sensor body that is illuminated by light from the lamp is coincident with a region of the sensor body where the majority of the fluorescence occurs. In another envisaged arrangement, the coupler could be dispensed with and the first 21 and second 19 fibres could be coupled directly to the sensor 1.

As will be appreciated, when the system is operated light from the lamp 23 travels down the first fibre 21 to the sensor 1. The sensor 1 fluoresces when illuminated with light from the lamp 23 and the fluorescence changes (for example the intensity of the fluorescence reduces) when the pH of the medium to which the sensor is exposed increases. Light due to fluorescence within the sensor travels from the sensor to the spectrometer 25 via the second fibre 19. The spectrometer 25 is coupled to a computing resource 27 such as a personal computer (PC) running appropriate software for analysing data output by the spectrometer 25.

In one envisaged implementation, as the pH of the medium increases the nitrogen on the imidazolyl group deprotonates and causes the intensity of fluorescent light travelling to the spectrometer to decrease, and from this decrease in intensity the pH of the medium can directly be inferred using the aforementioned equation.

In an envisaged implementation the fibres are all multimode fibres capable of transmitting UV/Visible light. The lamp 23 comprises an LED light source that emits light with a centre wavelength of between 370 and 380 nm (preferably 375 nm), and the spectrometer comprises an Ocean Optics USB2000 spectrometer (available from Ocean Optics, 830 Douglas Ave., Dunedin, FL 34698, USA - see also: www.oceanoptics.com).

In one envisaged implementation, the sensor and the first and second fibres 21 , 19 could be embedded within a structure when that structure is constructed (leaving tail ends of the fibres extending from the structure so that they can be coupled to the remainder of the system shown in Fig. 2). In another envisaged implementation, the fibres and sensor could be retrofitted to an existing structure.

Referring now to Fig. 3, there is provided a schematic representation of a typical fluorescence spectrum for the system 11 depicted in Fig. 2. As shown in Fig. 3, the spectrum identifies a first region 29 where the spectrometer is saturated with light from the source that is reflected from the sensor 1. The spectrum also includes a second peak 31 attributable to light from the fluorescing sensor body 3.

Fig. 4 is an illustrative calibration curve for sensors of the type depicted in Fig. 1 when immersed in media of increasing pH. As shown in Fig. 4, the sensor 1 shows a very good correlation between intensity ratio and high pH, for example for pH's of 10 and over, in particular for pH's of 12 and above. It is clear, therefore, that the sensor 1 is indeed suitable for detecting pH, and particularly well suited for pH sensing in highly alkaline environments where the pH is at least about 10 or higher.

Methods of synthesising illustrative pH sensitive fluorescent dye polymers will now be described with particular reference to Figs. 5 and 6 of the accompanying drawings.

In general terms, the sensor body 3 comprises a coumarin dye that was polymerised together with methacrylic acid and bis(acryloyl)piperazine in the presence of pluronic P84 as surfactant at 80 degrees centigrade in the dark for approximately 20 hours. The resultant hard bulk polymer was then crushed to provide a polymer powder for use in a sensor of the type shown in Fig. 1.

A first method of making a particular dye suitable for use in the sensor will be described hereafter with reference to Fig. 5 of the drawings. As shown in Fig. 5, a polymerisable pH sensitive dye can be prepared in five steps ((a) to (e)) starting from a commercially available compound: 3- aminophenol (labelled 33 - n.b. labels for compounds shown in Fig. 5 are referred to hereafter in bold type).

In step (a) of this method, 3-/V-(Carbethoxy)aminophenol (35) was prepared using a method similar to that reported in Maly, D.J., F. Leonetti, B.J. Backes, D.S. Dauber, J.L. Harris, C.S. Craik and J.A. Ellman, J. Org. Chem., 2002, 67, 910-915. To a two necked flask equipped with a condenser and a septum were added 3- aminophenol (33) (10.9 g, 100 mmol) and EtOAc (40 ml_). The mixture was heated to reflux for 30 min. Ethyl chloroformate (5.4 g, 4764 μΙ_, 50 mmol) was added via syringe over a 10 min period. The reaction mixture was left to stir for a further 20 min then allowed to cool to room temperature at which time a white precipitate formed. The precipitate was removed by filtration and washed with EtOAc (50 mL) and petroleum ether (50 mL). The combined filtrate was concentrated to give 3-/V-(Carbethoxy)aminophenol (35) as an off-white solid which was further purified by recrystallisation from toluene to afford 3-/V-(Carbethoxy)aminophenol (35) as a white solid.

In step (b) of this method, H₂S0₄ (80%, 40 mL) was pre-cooled in an ice bath. 3-N- (Carbethoxy)aminophenol (35) (1.8 g, 10 mmol) was added, followed by ethyl 4- chloroacetoacetone in portions. The mixture was stirred at room temperature under Ar for 19 hrs, after which it was poured into ice-water (50 mL) and left to stir for a further 30 min. The white precipitate formed was filtered, washed with H₂0 and recrystallised from EtOH to afford 4-Chloromethyl-7-/V-(Carbethoxy)aminocoumarin (37) as fine crystals

In step (c) of this method, 4-Chloromethyl-7-/V-(Carbethoxy)aminocoumarin (37) (563.4 mg, 2 mmol) was suspended in a mixture of concentrated H₂S0₄ (1.7 mL) and glacial acetic acid (1.7 mL). The mixture was heated to 125 °C for 2hrs. After cooling to room temperature, the yellow solution was poured into H₂0 and a voluminous precipitate was formed. 4 M NaOH aqueous solution was added to the mixture to bring the pH to approximately 9. The yellow precipitate was filtered, washed with H₂0, and recrystallised from EtOH to afford 4-Chloromethyl-7-aminocoumarin (39) as a pale yellow solid.

In step (d) of this method, NaH in mineral oil (60%, 40 mg) was added to a solution of 2-methyl-4-nitroimidazole (127.1 mg, 1 mmol) in dimethylformamide (DMF) (4 mL). The resulting mixture was heated to 1 10 °C for 10 min and then cooled down to 60 °C, after which 4-Chloromethyl-7-aminocoumarin (39) (209.6 mg, 1 mmol) suspended in DMF (4 mL) was added. The reaction mixture was left stirring at the same temperature for 18 hrs and then poured into ice. The precipitate formed was collected by filtration, washed with water and purified by flash chromatography on silica gel using CH₂CI₂-MeOH (8:2, v/v) as eluent to afford 7-amino-4-((2-methyl-4-nitro-1 /-/-imidazol-1-yl)methyl)-coumarin (41) as a yellow solid, which was further purified by recrystallisation from ethanol.

In step (e) of this method, a mixture of (300.3 mg, 1 mmol), vinylbenzylchloride (152.6 mg, 1 mmol, 1 mol equiv), potassium carbonate (400.8 mg, 2.9 mmol, 2.9 mol equiv), posstasium iodide (49.8 mg, 0.3 mmol, 0.3 mol equiv) and MeCN (12 mL) was heated to 100 °C for 2 days. The crude product was purified by flash chromatography on silica gel using CH₂CI₂-MeOH (8:2, v/v) as eluent to afford 7-(4-vinylbenzylamino)-4-((2-methyl-4- nitro-1 /-/-imidazol-1-yl)methyl)-coumarin (43) as a yellow solid.

To prepare a polymer of the dye resulting from step (e), 7-(4-vinylbenzylamino)-4-((2- methyl-4-nitro-1 /-/-imidazol-1-yl)methyl)-coumarin (43) (20.8 mg, 0.05 mmol), methacrylic acid (8.6 mg, 8.5 μΙ_, 0.1 mmol), 1 ,4-bis(acryloyl)piperrazine (97, 1 mg, 0.5 mmol) and pluronic P84 (84 mg) were weighed into a borosilicate glass vial and dissolved in dimethylformamide (500 μΙ_) . Azobis(isobutyronitrile) (AIBN) (5 mg) was then added. The vial was placed in a sonicating water bath until AIBN was fully dissolved, then purged thoroughly with argon for about 2 min before being tightly capped and sealed. Polymerisation was carried out at 80 °C in the dark for approximately 20 h. The resulting hard bulk polymer was then hand ground with a mortar and pestle until fine particles were obtained. The polymer particles were washed to remove unreacted materials by repeated incubation in MeOH (50 mL solvent each), centrifugation and re-suspension (4x0.5h incubations), followed by the same procedure with H₂0 (2x0.5 h incubations) and finally on a sintered filter with MeOH (50 mL). After washing, polymer particles were dried in vacuum and stored in the dark until use.

A second method of making a particular dye suitable for use in the sensor will be described hereafter with reference to Fig. 6 of the drawings. As shown in Fig. 6, a polymerisable pH sensitive dye can be prepared in three steps ((a) to (c)) starting from a commercially available compound: 3-bromophenol (45).

In step (a) of this method, H₂S0₄ (80%, 40 mL) was pre-cooled in an ice bath. 3- bromophenol (45) (1.73 g, 10 mmol) was added, followed by ethyl 4-chloroacetoacetone in portions. The mixture was stirred at room temperature under Ar for 22 hrs, after which it was poured into ice-water (50 mL) and left stirring for a further 30 min. The white precipitate formed was filtered, washed with H₂0, dried over phosphorus pentoxide and recrystallised from EtOH to afford 4-Chloromethyl-7-bromocoumarin (47) as a white solid

In step (b) of this method, NaH in mineral oil (60%, 80 mg) was added to a solution of 2-methyl-4-nitroimidazole (254.2 mg, 2 mmol) in DMF (8 mL). The mixture was heated to 1 10 °C for 10 min and then cooled down to 60 °C, after which 4-Chloromethyl-7- bromocoumarin (47) (547.0 mg, 2 mmol) suspended in DMF (8 mL) was added. The reaction mixture was left stirring at the same temperature for 20 hrs and then poured into ice. The precipitate formed was collected by filtration, washed with water, dried and recrystallised from EtOH to afford 7-bromo-4-((2-methyl-4-nitro-1 /-/-imidazol-1-yl)methyl)- coumarin (49) as an off-white solid.

In step (c) of this method, 7-vinylphenyl-4-((2-methyl-4-nitro-1 /-/-imidazol-1- yl)methyl)-coumarin (51 ) was prepared from 7-bromo-4-((2-methyl-4-nitro-1 /-/-imidazol-1- yl)methyl)-coumarin (49) via a Suzuki coupling reaction {see: (i) Beller, M. and C. Bolm, eds. Transition metals for organic synthesis. Transition metal-catalysed cross coupling reactions, ed. H. Geissler. Vol. 1. 1998, Wiley-VCH: Weinheim; (ii) Diederich, F. and P.J. Stang, eds. Metal-catalyzed cross-coupling reactions. 1998, Wiley-VCH: Weinheim; and (iii) Miyaura, N. and A. Suzuki, Chem. Rev., 1995, 95, 2457-2483} with vinylphenylboronic acid. A mixture of 7-bromo-4-((2-methyl-4-nitro-1 /-/-imidazol-1-yl)methyl)-coumarin (49) (400.6 mg, 1.1 mmol), 4-vinylphenylboronic acid (244.2 mg, 1.65 mmol, 1.5 mol equiv), posstasium carbonate (570 mg, 4.125 mmol, 3.75 mol equiv) and dioxane (1 1 mL) was stirred in a two necked flask at room temperature under argon for 0.5 hrs. Tetrakis(triphenylphosphine)palladium(0) (63.6 mg, 0.055 mmol, 5 mol %) was added. A condenser was fitted and the flask was evacuated and filled with argon three times before being heated to 80 °C. The reaction was left at 80 °C in the dark for 41 hrs. After cooling to room temperature, ethylacetate (EtOAc) was added. The organic phase was washed with water (3 ^χ 50 mL), saturated aqueous NaCI (50 mL), dried over MgS0₄, filtered, concentrated in vacuo to give the crude product which was purified by flash chromatography on silica gel with CH₂CI₂-EtOAc (1 :9, v/v, v/v) as eluent to give 7-vinylphenyl-4-((2-methyl-4-nitro-1 /-/-imidazol-1-yl)methyl)-coumarin (51 ) as an orange solid, which was further purified by recrystallisation from EtOH-EtOAc (5: 1 , v/v) to give orange crystals.

To prepare a polymer of the dye resulting from step (c), 7-vinylphenyl-4-((2-methyl-4- nitro-1 /-/-imidazol-1-yl)methyl)-coumarin (51) (19.4 mg, 0.05 mmol), methacrylic acid (8.6 mg, 8.5 μί, 0.1 mmol), 1 ,4-bis(acryloyl)piperrazine (97, 1 mg, 0.5 mmol) and pluronic P84 (84 mg) were weighed into a borosilicate glass vial and dissolved in dimethylformamide (500 μί) . Azobis(isobutyronitrile) (AIBN) (5 mg) was then added. The vial was placed in a sonicating water bath until AIBN was fully dissolved, then purged thoroughly with argon for about 2 min before being tightly capped and sealed. Polymerisation was carried out at 80 °C in the dark for approximately 20 h. The resulting hard bulk polymer was then hand ground with a mortar and pestle until fine particles were obtained. The polymer particles were washed to remove unreacted materials by repeated incubation in MeOH (50 mL solvent each), centrifugation and re-suspension (4x0.5h incubations), followed by the same procedure with H₂0 (2x0.5 h incubations) and finally on a sintered filter with MeOH (50 mL). After washing, polymer particles were dried in vacuum and stored in the dark until use.

It will be apparent from the foregoing, that the present application discloses novel pH sensitive dyes that can be polymerised, and subsequently incorporated into a sensor that can be used in a system for determining pH. The sensor and optic fibres employed in the system are capable of surviving in highly alkaline environments (for example, environments with a pH of about 10 or higher), and hence the system disclosed herein provides an effective alternative to existing monitoring systems.

It will be appreciated that whilst various aspects and embodiments of the present invention have heretofore been described, the scope of the present invention is not limited to the particular arrangements set out herein and instead extends to encompass all arrangements, and modifications and alterations thereto, which fall within the scope of the appended claims.

It should also be noted that whilst the accompanying claims set out particular combinations of features described herein, the scope of the present invention is not limited to the particular combinations hereafter claimed, but instead extends to encompass any combination of features herein disclosed.

Claims

1. An optical sensor for pH monitoring in highly alkaline mediums having a pH of at least about 10 or higher, the sensor comprising: a sensor body that fluoresces when illuminated by light, the sensor body being configured to exhibit a change in fluorescence in response to changing pH in highly alkaline mediums having a pH of at least about 10 or higher, the sensor further comprising means for coupling the sensor body to a source of illumination.

2. An optical sensor according to Claim 1 , wherein said change in fluorescence comprises a change in fluorescence intensity.

3. An optical sensor according to Claim 1 or 2, wherein the sensor body exhibits a reduction in fluorescence intensity when the pH of a medium to which the sensor body is exposed increases.

4. An optical sensor according to any of claims 1 to 3, wherein the fluorescent sensor body comprises a polymerised coumarin dye that bears an imidazolyl group..

5. An optical sensor according to Claim 5, wherein the sensor body comprises polymerised 7-(4-vinylbenzylamino)-4-((2-methyl-4-nitro-1 /-/-imidazol-1-yl)methyl)-coumarin or polymerised 7-vinylphenyl-4-((2-methyl-4-nitro-1 /-/-imidazol-1-yl)methyl)-coumarin.

6. An optical sensor according to any preceding claim, wherein sensor body comprises a layer of particles.

7. An optical sensor according to any preceding claim, wherein the optical coupling means is configured to be optically transparent to a range of wavelengths including that at which the sensor body fluoresces.

8. An optical sensor according to Claim 7, wherein the optical coupling means is of quartz.

9. An optical sensor according to Claim 7 or 8, wherein the sensor body is abutted against the optical coupling means.

10. An optical sensor according to any preceding claim, wherein the sensor body fluoresces when illuminated with light having a centre wavelength of about 370 to 380nm, preferably about 375nm.

1 1. An optical sensor according to any preceding claim, wherein said sensor body is sandwiched between said optical coupling means and a permeable cover.

12. An optical sensor according to Claim 11 wherein the cover includes a plurality of pores, each of about 20 microns in diameter.

13. An optical sensor according to Claim 1 1 or 12, wherein said cover is of nylon.

14. An optical sensor according to any preceding claim, wherein said sensor body being configured to exhibit a change in fluorescence in response to changing pH in highly alkaline mediums having a pH of about 12 or higher.

15. A system for determining pH, the system comprising:

an optical sensor according to any of Claims 1 to 14;

a lamp;

a spectrometer, and

means for coupling the lamp to the optical coupling means of the optical sensor, and for coupling the optical coupling means of the sensor to the spectrometer.

16. A system according to Claim 15, wherein the means for coupling the lamp to the optical coupling means of the optical sensor comprises an optic fibre.

17. A system according to Claim 15 or 16, wherein the means for coupling the optical coupling means of the optical sensor to the spectrometer comprises an optic fibre.

18. A system according to any of Claims 15 to 17 comprising a first optic fibre coupling the lamp to the optical sensor, and a second optic fibre coupling optical sensor to the spectrometer.

19. A system according to Claim 18, further comprising a fibre coupler for coupling said first and second optic fibres together in a single cable so that light from the lamp is directed via the first optic fibre to illuminate a first part of said sensor body, and so that fluorescence from said first part is directed via said second fibre to said spectrometer.

20. A system according to any of Claims 14 to 18, further comprising a computing resource coupled to the spectrometer for the receipt of data therefrom.

21. A method of synthesising a pH sensitive fluorescent dye polymer, the method comprising the steps of: (a) synthesising a pH sensitive polymerisable coumarin dye that bears an imidazolyl group, and (b) polymerising the dye to provide a pH sensitive fluorescent polymer.

22. A method of synthesising a pH sensitive polymerisable fluorescent coumarin dye, the method comprising:

(e) reacting 7-amino-4-((2-methyl-4-nitro-1 /-/-imidazol-1-yl)methyl)-coumarin with vinylbenzylchloride in acetonitrile in the presence of potassium carbonate and posstasium iodide to provide 7-(4-vinylbenzylamino)-4-((2-methyl-4-nitro-1 /-/-imidazol-1-yl)methyl)- coumarin.

23. A method of synthesising a pH sensitive polymerisable fluorescent coumarin dye, the method comprising:

24. A pH sensitive polymensable coumarin dye of the formula:

A pH sensitive polymensable coumarin dye of the formula: