Chemical Sensors Comprising Fluorescent Conjugated Polymers as Sensitive Materials, and Their use in the Detection or Assaying of Nitro Compounds

Abstract

The invention relates to chemical sensors comprising fluorescent conjugated polymers as sensitive materials and to their use in detecting or assaying nitro compounds, in particular nitroaromatic compounds.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents the change in the intensity of the fluorescence emitted by a first example of the sensor in accordance with the invention (λ_emission: 507 nm; λ_excitation: 404 nm) when this sensor is exposed alternately to pure nitrogen and to mixtures of nitrogen and of 2,4-dinitrotrifluoromethoxybenzene (DNTFMB).

FIG. 2 represents the change in the intensity of the fluorescence emitted by the first example of a sensor in accordance with the invention (λ_emission: 507 nm; λ_excitation: 404 nm) when this sensor is exposed alternately to pure nitrogen and to mixtures of nitrogen and of DNTFMB, dichloromethane, cyclohexane, methyl ethyl ketone, toluene, methyl isobutyl ketone, ethyl acetate and, again DNTFMB, respectively.

FIG. 3 represents the variation in the intensity of the fluorescence emitted by the first example of a sensor in accordance with the invention (λ_emission: 507 nm; λ_excitation: 404 nm) when this sensor is exposed a number of times to a mixture of nitrogen and of DNTFMB, each exposure lasting 10 minutes and the exposures being spread over a period of 96 days.

FIG. 4 represents the change in the intensity of the fluorescence emitted by a second example of a sensor in accordance with the invention (λ_emission: 500 nm; λ_excitation: 397 nm) when this sensor is exposed alternately to pure nitrogen and to mixtures of nitrogen and of DNTFMB.

FIG. 5 represents the change in the frequency of vibration of the quartz crystal of a third example of a sensor in accordance with the invention when this sensor is exposed alternately to ambient air and to mixtures of ambient air and of DNTFMB vapours.

FIG. 6 represents the change in the intensity of the fluorescence emitted by a fourth example of a sensor in accordance with the invention (λ_emission: 491 nm; λ_excitation: 397 nm) when this sensor is exposed alternately to pure nitrogen and to a mixture of nitrogen and of DNTFMB.

DETAILED ACCOUNT OF SPECIFIC EMBODIMENTS

In the examples which follow, 2,4-dinitrorifluoromethoxybenzene (DNTFMB) is used as nitro compound due to its great similarity to dinitrotoluene (DNT), which is the nitro derivative most generally present in the chemical signature of mines based on trinitrotoluene (TNT).

Furthermore, in Examples 1 to 4 and 6, the measurements of intensity of fluorescence are carried out using a FluoroMax-3 fluorimeter from Jobin Yvon, under dynamic conditions in a cell swept at 20 l/h. These measurements are carried out using the excitation wavelength of the sensitive material resulting in the best signal/noise ratio for the acquisition of the intensities of fluorescence and at the emission wavelength giving the maximum intensities of fluorescence for this excitation wavelength. The emission and excitation wavelengths thus selected are specified in each example.

Example 1

Detection Of DNTFMB By A First Example Of A Sensor In Accordance With The Invention

In this example, the preparation is carried out of a sensor, the operation of which is based on the variation in the intensity, of the fluorescence emitted by the sensitive material which this sensor comprises in the presence of a nitro compound.

In the case in point, the sensitive material is composed of a polymer comprising a repeat unit of specific formula (I-A-a) in which R⁵ to R¹³ and R¹⁶═H and R¹⁴ and R¹⁵═OC₈H₁₇, in the form of a thin film which covers one of the faces of a substrate made of glass of optical quality.

To do this, the polymer is synthesized from (1R,2R)-diaminocyclohexane and 4-bromobenzaldehyde, as described by J. P. Lere-Porte et al. in the reference [5], and then deposited on the glass substrate by carrying out three sprayings, each of 0.2 second, of a solution of the said polymer in chloroform with a concentration of 1.5 g/l.

The thin film thus obtained exhibits an intensity of fluorescence of 2×10⁷ cps (counts per second; λ_emission: 507 nm; λ_excitation: 404 nm)

The sensor is successively exposed to:

• pure nitrogen for 30 minutes,
• DNTFMB at a concentration of 0.5 ppm in nitrogen for 10 minutes,
• pure nitrogen for 60 minutes,
• DNTFMB at a concentration of 0.1 ppm in nitrogen for 10 minutes,
• pure nitrogen for 50 minutes,
• DNTFMB at a concentration of 0.03 ppm in nitrogen for 10 minutes and, finally,
• pure nitrogen for 15 minutes, the nitrogen and the DNTFMB being, in all cases, in the gas form at ambient temperature.

FIG. 1 illustrates the change in the intensity of fluorescence emitted by the sensor during these exposures (λ_emission: 507 nm; λ_excitation: 404 nm).

In this figure, curve A represents the values of the intensity of fluorescence (I), expressed in cps, as a function of the time (t), expressed in seconds, while curve B represents the values of the concentration of DNTFMB (C), expressed in ppm, also as a function of the time.

Example 2

Demonstration Of The Selectivity Of The First Example Of A Sensor In Accordance With The Invention For Nitro Compounds With Regard To Solvents

In this example, a sensor identical to that described in Example 1 is used.

This sensor is successively exposed to:

• pure nitrogen for 90 minutes,
• DNTFMB at a concentration of 1 ppm in nitrogen for 10 minutes,
• pure nitrogen for 30 minutes,
• dichloromethane at a concentration of 675 ppm in nitrogen for 10 minutes,
• pure nitrogen for 30 minutes,
• cyclohexane at a concentration of 540 ppm in nitrogen for 10 minutes,
• pure nitrogen for 30 minutes,
• methyl ethyl ketone at a concentration of 360 ppm in nitrogen for 10 minutes,
• pure nitrogen for 80 minutes,
• toluene in a concentration of 180 ppm in nitrogen for 10 minutes,
• pure nitrogen for 25 minutes,
• methyl isobutyl ketone at a concentration of 90 ppm in nitrogen for 10 minutes,
• pure nitrogen for 30 minutes,
• ethyl acetate at a concentration of 720 ppm in nitrogen for 10 minutes,
• pure nitrogen for 25 minutes and, finally,
• DNTFMB at a concentration of 1 ppm in nitrogen for 6 minutes, the nitrogen, the DNTFMB and the other solvents being, in all cases, in the gas form and at ambient temperature.

FIG. 2 illustrates the change in the intensity of fluorescence (I), expressed in cps (λ_emission: 507 nm; λ_excitation: 404 nm), as emitted by the sensor as a function of time (t), expressed in seconds. The f1 indicates the beginning of the first exposure to the nitrogen/DNTFMB mixture; the f2 indicates the beginning of the exposure to the nitrogen/dichloromethane mixture; the arrow f3 indicates the end of exposure to the nitrogen/ethyl acetate mixture, while the arrow f4 indicates the beginning of the second exposure to the nitrogen/DNTFMB mixture.

This figure shows that the exposure of the sensor to solvents, such as dichloromethane, cyclohexane, methyl ethyl ketone or toluene, does not bring about a response of the sensor comparable to that obtained when the latter is exposed to a nitro compound. Furthermore, the response of the sensor obtained during its second exposure to DNTFMB shows that the solvents have not affected the performance of the sensor with regard to nitro compounds.

Example 3

Demonstration That The Detection Properties Of The First Example Of A Sensor In Accordance With The Invention Are Maintained Over Time

In this example, a sensor identical to that described in Example 1 is used.

This sensor is exposed a number of times to DNTFMB at a concentration of 1 ppm in nitrogen, each exposure lasting 10 minutes, the first exposure taking place on the day of the deposition of the thin film of polymer on the glass substrate (D0) and the following exposures at time intervals over a period of 96 days. The sensor is stored in the ambient air between two exposures to DNTFMB.

FIG. 3 illustrates the values of the variations in the intensity of fluorescence (ΔI) emitted by the sensor during the exposures to the ambient air/DNTFMB mixture carried out D0, D8, D42 and D96 (λ_emission: 507 nm; λ_excitation: 404 nm) , these values being determined for each exposure as follows:

• ΔI=intensity of fluorescence emitted at the time t₀ of an exposure—intensity of fluorescence emitted at the time too min of this same exposure.

This figure shows that, although the variation in the intensity of fluorescence emitted by the sensor tends to fall over time, the sensor is still capable of detecting DNTFMB at the concentration of 1 ppm 96 days after deposition of the thin film of the polymer.

Example 4

Detection Of DNTFMB By A Second Example Of A Sensor In Accordance With The Invention

In this example, the preparation is carried out of a sensor, the operation of which is also based on the variation in the intensity of the fluorescence emitted by the sensitive material of this sensor in the presence of a nitro compound and in which the sensitive material is composed of a polymer comprising a repeat unit of formula (I-A-b) in which R⁵ to R¹³ and R¹⁶═H and R¹⁴ and R¹⁵═OC₈H₁₇, in the form of a thin film which covers one of the faces of a substrate made of glass of optical quality.

The polymer is synthesized from (1R, 2R)-diaminocyclohexane and 4-bromobenzaldehyde, as described by J. P. Lere-Porte et al. in the reference [6], and then deposited on the glass substrate by drop coating with a solution of the said polymer in methylene chloride at a concentration of 1 g/l.

The solvent is evaporated at ambient temperature and atmospheric pressure, so as to obtain a thin film exhibiting an intensity of fluorescence of 3.5×10⁶ Cps (λ_emission: 500 nm; λ_excitation: 397 nm)

The sensor is successively exposed to:

• pure nitrogen for 45 minutes,
• DNTFMB at a concentration of 1 ppm in nitrogen for 10 minutes,
• pure nitrogen for 60 minutes,
• DNTFMB at a concentration of 0.1 ppm in nitrogen for 10 minutes and, finally,
• pure nitrogen for 40 minutes, the nitrogen and the DNTFMB being, in all cases, in the gas form and at ambient temperature.

FIG. 4 illustrates the change in the intensity of fluorescence emitted by the sensor during these exposures (λ_emission: 500 nm; λ_excitation: 397 nm).

In this figure, curve A represents the values of the intensity of fluorescence (I), expressed in cps, as a function of the time (t), expressed in seconds, while curve B represents the values of the variation in the concentration of DNTFMB (C), expressed in ppm, also as a function of the time.

Example 5

Detection Of DNTFMB By A Third Example Of A Sensor In Accordance With The Invention

In this example, a quartz microbalance sensor is prepared.

To do this, the two faces of an AT-cut quartz crystal with a frequency of vibration of 9 MHz equipped with two circular gold measurement electrodes (QA9RA-50 model, Ametek Precision Instruments) are covered with a thin film of a polymer comprising a repeat unit of specific formula (I-A-a) in which R⁵ to R¹³ and R¹⁶═H and R¹⁴ and R¹⁵═OC₈H₁₇.

This thin film is obtained by carrying out, on each face of the quartz crystal, five sprayings, each of 0.2 second, of a solution of the said polymer in chloroform with a concentration of 1.5 g/l. The formation of this film is reflected by a variation in the frequency of vibration of the quartz of 0.6 kHz.

The sensor is successively exposed to:

• ambient air for 9 minutes,
• DNTFMB at a concentration of 3 ppm in ambient air for 10 minutes,
• ambient air for 38 minutes,
• DNTFMB at a concentration of 3 ppm in ambient air for 10 minutes and, finally,
• ambient air for 15 minutes.

FIG. 5 illustrates the change in the frequency of vibration of the quartz crystal during these exposures.

In this figure, curve A represents the values of the frequency of vibration (F), expressed in Hz (hertz), as a function of the time (t), expressed in seconds, while curve B represents the values of the concentration of DNTFMB (C), expressed in ppm, also as a function of the time.

Example 6

Detection Of DNTFMB By A Fourth Example Of The Sensor In Accordance With The Invention

In this example, the preparation is carried out of a sensor, the operation of which is based on the variation in the intensity of this fluorescence emitted by the sensitive material of this sensor in the presence of a nitro compound and in which the sensitive material is composed of a polymer comprising a repeat unit of formula (I-B-a) in which R⁵, R⁶, R⁹, R¹³ and R¹⁶═H and R¹⁴ and R¹⁵═OC₈H₁₇, in the form of a thin film which covers one of the faces of a substrate made of glass of optical quality.

The polymer is synthesized from (1R, 2R)-diaminocyclohexane and 5-bromothiophene-2-carboxaldehyde, as described by J. P. Lere-Porte et al. in the reference [5], and then deposited on the glass substrate by carrying out 4 sprayings, each of 0.15 second, of a solution of the said polymer in tetrahydrofuran with a concentration of 3 g/l.

The solvent is evaporated at ambient temperature under atmospheric pressure, so as to obtain a thin film exhibiting an intensity of fluorescence of 2×10 cps (λ_emission: 491 nm; λ_excitation: 397 nm) The sensor is successively exposed to:

• pure nitrogen for 25 minutes,
• DNTFMB at a concentration of 400 ppb in nitrogen for 5 minutes and
• pure nitrogen for 100 minutes, the nitrogen and the DNTFMB being in the gas form and at ambient temperature.

FIG. 6 illustrates the change in the intensity of fluorescence emitted by the sensor during these exposures (λ_emission: 491 nm; λ_excitation: 397 nm).

In this figure, curve A represents the values of the intensity of fluorescence (I), expressed as cps, as a function of the time (t), expressed in seconds, while curve B represents the values of the variation in the concentration of DNTFMB (C), expressed in ppm, also as a function of the time.

REFERENCES CITED

• [1] M. J. Sailor et al., SPIE Proceedings, The International Society of Optical Engineering, 3713, 1999, 54-65
• [2] K. J. Albert and D. R. Walt, Anal. Chem., 72, 2000, 1947
• [3] B. Valeur, Molecular Fluorescence: Principles and Applications, 2002, published by Wiley VCH, New York
• [4] J. A. O. Sanchez-Pedrono et al., Anal. Chem. Acta, 182, 1986, 285
• [5] J. P. Lere-Porte et al., Chem. Commun., 24, 2002, 3020-3021
• [6] J. P. Lere-Porte et, al., Tet. Lett., 42, 2001, 3073-3076

Claims

1-27. (canceled)

28. Chemical sensor comprising, as sensitive material, at least one polymer comprising at least one repeat unit corresponding to the general formula (I) below:

29. Sensor according to claim 28, in which the polymer comprises at least one repeat unit of general formula (I) in which A1, A2 and A3 are each a phenyl group.

30. Sensor according to claim 29, in which the polymer comprises at least one repeat unit corresponding to the specific formula (I-A) below:

31. Sensor according to claim 28, in which the polymer comprises at least one repeat unit of general formula (I) in which A1 and A2 are each a thienyl group and A3 is a phenyl group.

32. Sensor according to claim 31, in which the polymer comprises at least one repeat unit corresponding to the specific formula (I-B) below:

33. Sensor according to claim 28, in which the polymer comprises at least one repeat unit of general formula (I) in which B represents a group corresponding to one of the formulae (a), (b) and (c).

34. Sensor according to claim 33, in which the polymer comprises at least one repeat unit of general formula (I) in which B represents a group corresponding to one of the formulae (a), (b) and (c) where X is a chiral hydrocarbon group of C2 symmetry.

35. Sensor according to claim 34, in which the polymer comprises a repeat unit of general formula (I) in which B represents a group corresponding to one of the formulae (a), (b) and (c) where X is a hydrocarbon group chosen from the groups of formulae (i) to (vii) below:

36. Sensor according to claim 30, in which the polymer comprises at least one repeat unit corresponding to one of the specific formulae (I-A-a), (I-A-b) and (I-A-c) below:

37. Sensor according to claim 30, in which the polymer comprises at least one repeat unit of specific formula (I-A) in which at least one of R5 to R16 represents a linear or branched C1 to C20 or a C5 to C10 alkoxy group, that or those of R5 to R16 which do not represent an alkoxy group, if there are any, then representing a hydrogen atom.

38. Sensor according to claim 36, in which the polymer comprises at least one repeat unit of specific formula (I-A-a), (I-A-b) or (I-A-c) in which R14 and R15 represent a linear or branched C1 to C20 or C5 to C10 alkoxy group while R5 to R13 and R16 represent a hydrogen atom.

39. Sensor according to claim 38, in which the polymer comprises at least one repeat unit of specific formula (I-A-a) or (I-A-b) in which R14 and R15 represent an octoxy group while R5 to R13 and R16 represent a hydrogen atom.

40. Sensor according to claim 32, in which the polymer comprises at least one repeat unit corresponding to one of the specific formulae (I-B-a), (I-B-b) and (I-B-c) below:

41. Sensor according to claim 32, in which the polymer comprises at least one repeat unit of specific formula (I-B) in which at least one of R5, R6, R9, R10 and R13 to R16 represents a linear or branched C1 to C20 or C5 to C10 alkoxy group, that or those of R5, R6, R9, R10 and R13 to R16 which do not represent an alkoxy group, if there are any, then representing a hydrogen atom.

42. Sensor according to claim 40, in which the polymer comprises at least one repeat unit of specific formula (I-B-a), (I-B-b) or (I-B-c) in which R14 and R15 represent a linear or branched C1, to C20 or C5 to C10 alkoxy group while R5, R6, R9, R10, R13 and R16 represent a hydrogen atom.

43. Sensor according to claim 42, in which the polymer comprises at least one repeat unit of specific formula (I-B-a) in which R14 and R15 represent an octoxy group while R5, R6, R9, R10, R13 and R16 represent a hydrogen atom.

44. Sensor according to claim 28, in which the polymer is a homopolymer.

45. Sensor according to claim 28, in which the polymer is present in the form of a thin film covering one or both faces of a substrate.

46. Sensor according to claim 45, in which the thin film measures from 10 angstroms to 100 microns in thickness.

47. Sensor according to claim 28, which is a fluorescence-based optical sensor.

48. Sensor according to claim 28, which is a gravimetric sensor.

49. Sensor according to claim 28, which is of multisensor type and which comprises one or more fluorescence-based sensors and/or one or more gravimetric sensors, at least one of these sensors comprising at least one polymer comprising at least one repeat unit of general formula (I) as sensitive material.

50. Method of detecting or assaying one or more nitro compounds, which comprises the use of a chemical sensor according to claim 28.

51. Method according to claim 50, in which the nitro compound or compounds are in the gas form.

52. Method according to claim 50, in which the nitro compound or compounds are chosen from nitroaromatic compounds, nitramines, nitrosamines and nitric esters.

53. Method according to claim 50, in which the nitro compound or compounds are chosen from nitrobenzene, dinitrobenzene, trinitrobenzene, nitrotoluene, dinitrotoluene, trinitrotoluene, dinitrofluorobenzene, dinitrotrifluoromethoxybenzene, aminodinitrotoluene, dinitrotrifluoromethylbenzene, chlorodinitrotrifluoromethylbenzene, hexanitrostilbene, trinitrophenol, cyclotetramethylenetetranitramine, cyclotrimethylenetrinitramine, trinitrophenylmethylnitramine, nitrosodimethylamine, pentrite, ethylene glycol dinitrate, diethylene glycol dinitrate, nitroglycerine or nitroguanidine.

54. Method according to claim 50 for the detection of explosives.