Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
  • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
  • G01N21/64—Fluorescence; Phosphorescence
  • G01N21/6428—Measuring fluorescence of fluorescent products of reactions or of fluorochrome labelled reactive substances, e.g. measuring quenching effects, using measuring "optrodes"
  • G01N21/643—Measuring fluorescence of fluorescent products of reactions or of fluorochrome labelled reactive substances, e.g. measuring quenching effects, using measuring "optrodes" non-biological material
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N31/00—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods
  • G01N31/22—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods using chemical indicators
  • G01N31/221—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods using chemical indicators for investigating pH value
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/75—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated
  • G01N21/77—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator
  • G01N2021/7769—Measurement method of reaction-produced change in sensor
  • G01N2021/7786—Fluorescence

Definitions

• This invention relates to optical sensors, and systems employing such sensors.
• the sensors are configured to be responsive to the pH of a highly alkaline medium to which the sensor is exposed.
• 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.
• building materials such as, for example: concrete, cement, mortar (e.g. limestone mortar)
• 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.
• 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.
• the change in fluorescence comprises a change in fluorescence intensity.
• 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:
• Another aspect of the invention relates to a method of synthesising a pH sensitive polymerisable fluorescent coumarin dye, the method comprising:
• 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:
• 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. 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;
• 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
• the senor 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:
• 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
• pKa is the variable fitting parameter - which is the pH where 50% of the dye population in solution is protonated.
• 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.
• 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
• 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.
• 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.
• 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.
• 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.
• 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.
• 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
• 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.
• 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.
• the coupler could be dispensed with and the first 21 and second 19 fibres could be coupled directly to the sensor 1.
• 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.
• PC personal computer
• 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.
• 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).
• the senor 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).
• the fibres and sensor could be retrofitted to an existing structure.
• Fig. 3 there is provided a schematic representation of a typical fluorescence spectrum for the system 11 depicted in Fig. 2.
• 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.
• 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.
• 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 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).
• 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.
• 3- aminophenol (33) (10.9 g, 100 mmol)
• EtOAc 40 ml_
• step (b) of this method H 2 S0 4 (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 H 2 0 and recrystallised from EtOH to afford 4-Chloromethyl-7-/V-(Carbethoxy)aminocoumarin (37) as fine crystals
• step (c) of this method 4-Chloromethyl-7-/V-(Carbethoxy)aminocoumarin (37) (563.4 mg, 2 mmol) was suspended in a mixture of concentrated H 2 S0 4 (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 H 2 0 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 H 2 0, and recrystallised from EtOH to afford 4-Chloromethyl-7-aminocoumarin (39) as a pale yellow solid.
• 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.
• DMF dimethylformamide
• the precipitate formed was collected by filtration, washed with water and purified by flash chromatography on silica gel using CH 2 CI 2 -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.
• 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 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 H 2 0 (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 polymerisable pH sensitive dye can be prepared in three steps ((a) to (c)) starting from a commercially available compound: 3-bromophenol (45).
• step (a) of this method H 2 S0 4 (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 H 2 0, dried over phosphorus pentoxide and recrystallised from EtOH to afford 4-Chloromethyl-7-bromocoumarin (47) as a white solid
• 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.
• 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.
• 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 ⁇ , 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 ⁇ ) . Azobis(isobutyronitrile) (AIBN) (5 mg) was then added.
• AIBN Azobis(isobutyronitrile)
• 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 H 2 0 (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.
• 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.

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