RU2522902C1 - Luminescent sensor for ammonia vapours - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: sensor includes semiconductor nanocrystals (quantum dots), imbedded into a near-wall layer of track pores of polyethylene terephthalate membranes, with the pores remaining empty. If ammonia vapours are present in an air sample, ammonia molecules bind with quantum dot surfaces, which results in decrease of quantum dot luminescence.

EFFECT: invention solves the tasks of increasing sensitivity, accuracy of determination of ammonia vapour concentration, terms of exploitation and simplification of the sensor manufacturing.

5 dwg, 1 ex

Description

The invention relates to devices and materials for detecting and determining the concentration of ammonia vapors in the atmosphere or air sample (chemical sensors) and can be used in medicine, biology, ecology and various industries.

Known are “Sensors for ammonia” based on electrochemical methods for the detection of ammonia vapors, where there is a change in the resistance of the conductive material or electrolyte as a result of its interaction with ammonia molecules (US Patent No. 5252292, IPC G01N 27/04, application 524562, priority date 05.17.1990 , publication date 10/12/1993,) [1], (US Patent No. 3,649,055, IPC G01N 27/30, application 803781, priority date 03/03/1969, publication date 02/14/1972) [2]. The disadvantages of these devices are the presence of a source (electric resistance) of the matrix in the absence of analyte - impossible to implement a null method, a sufficiently narrow dynamic range of sensitivity (20-100 mn ^-1), sensitive to the signal level of the ambient environment conditions (temperature and humidity) , inability to remotely register a signal.

Sensors for ammonia vapors are known based on a change in the electronic absorption spectrum of a polymer film upon contact with ammonia molecules "Polyaniline-based ammonia detector" (US Patent No. US 6406669 B1, IPC G01N 27/77, application 09 / 760,121, priority date 01/12/2001 , publication date 06/18/2002) [3]. Such a sensor has a low inertia, and is characterized by a linear response over a wide concentration range from 180 to 18000 million ^-1. Known colorimetric gas sensors for ammonia vapors based on a hydrophobic microporous membrane with an embedded organic dye interacting with ammonia molecules "Sensor for ammonia based on a hydrophobic membrane" (US Patent No. US 2003/0113932 A1, IPC G01N 21/77, application 10 / 024670, priority date 12/14/2001, publication date 6/19/2003) [4]. However, sensors based on absorption detection methods are several orders of magnitude inferior in sensitivity to detection devices based on a change in the luminescent signal and, as a result, fundamentally have significantly worse sensitivity compared to luminescent sensors.

Closest to the claimed invention and adopted as a prototype is a sensor for ammonia vapors containing a pH-sensitive fluorophore that changes the luminescence intensity in the presence of ammonia molecules due to deprotonation of the fluorophore, embedded in a hydrophobic polymer membrane permeable to ammonia molecules "Hydrophobic fluorescent polymer ammonia "(US Patent No. 6013529, IPC G01N 33/00, application 08/906711, priority date 08/05/1997, publication date 11/01/2000) [5]. The prototype has the following disadvantages.

1. The need for careful selection of the polymer, when the molecules of the organic fluorophore are introduced into it, deprotonation of the latter will not occur.

2. A fairly complex technologically intensive process for the manufacture of a polymer matrix, in which the molecules of the organic fluorophore must be distributed evenly throughout the entire volume of the matrix in an isolated state.

3. Organic fluorophores have low photostability and, as a result, a change in the luminescence response from the matrix with an embedded organic fluorophore can be associated both with the presence of ammonia molecules and with photodegradation of the fluorophore itself. This circumstance fundamentally reduces the accuracy of detecting the response from the sensor element and, accordingly, leads to a decrease in its sensitivity.

The problem of increasing the sensitivity and service life while simplifying the manufacturing technology of the sensor is being solved.

The essence of the invention lies in the fact that as a fluorophore brightly luminescent semiconductor nanocrystals of a spherical shape (quantum dots) are used, the luminescence intensity of which decreases upon adsorption of ammonia molecules on the surface of quantum dots in proportion to the concentration of ammonia in the sample. Quantum dots are embedded in the parietal layer of pores of polyethylene terephthalate track membranes in such a way that the pores themselves remain free, which allows an air sample to be pumped through the sample and, accordingly, to lower the sensitivity threshold of the sensor.

The proposed sensor for the detection of ammonia vapor has the following advantages:

1. Increasing the sensitivity and accuracy of determining the concentration of ammonia vapor due to the ability to pump through the sensor element a large volume of an air sample containing ammonia vapor. This condition is achieved by the fact that quantum dots are introduced into the parietal layer of the through pores of the track membrane, and the pores themselves remain free. Obviously, the forced pumping of a large volume of the analyzed air sample will lead to a decrease in the lower limit of detectability of ammonia vapors compared to sensor elements based on polymer membranes that do not have through track pores of nanometer or micron diameter.

2. The increased life of the sensor element, which is due to the better photostability of quantum dots in comparison with the photostability of organic fluorophores.

3. Simplification of the sensor manufacturing technology consists in the fact that to create a sensor element sensitive to ammonia vapors, it is enough to impregnate a polyethylene terephthalate membrane, which is produced on an industrial scale, with a solution of hydrophobic semiconductor quantum dots. In this case, quantum dots are introduced into the wall layers of track pores in a quasi-isolated state, the spatial distribution of quantum dots over the matrix volume is determined by the distribution of track pores, the density of which has characteristic values of 10 ⁸ ÷ 10 ⁹ pores / cm ² .

The essence of the invention is illustrated in figures 1-5, which show:

Figure 1. Schematic representation of a polymer membrane with semiconductor quantum dots embedded in the surface layers of track pores.

Figure 2. Schematic illustration of the installation for the controlled supply / pumping of ammonia vapors: 1 - polyethylene terephthalate track membrane with embedded CdSe / ZnS quantum dots; 2 - a chamber filled with ammonia vapors; 3 - valve; 4 - a chamber with an aqueous solution of ammonia; 5 - tight stopper; 6 - an aqueous solution of ammonia; 7 - valve; 8 - tap to remove ammonia vapor from the chamber 2.

Figure 3. Luminescence spectra of a polymer track membrane sample with embedded CdSe / ZnS quantum dots with a core diameter of 2.5 nm, excitation by light with a wavelength of 405 nm: 1 - before interaction with ammonia vapors; 2 - the sample after aging in an ammonia vapor (C _{vapor ammonia} = 13 million ^-1) for 2 minutes; the inset shows the absorption spectrum of the sample after interaction with ammonia vapors.

Figure 4. Dependence of the degree of luminescence quenching (Q = 1-I / I ₀ , where I ₀ and I are the luminescence intensities of quantum dots before and after the interaction of the sample with ammonia vapors, respectively) of CdSe / ZnS quantum dots with a core diameter of 2.5 nm embedded in a polyethylene terephthalate track membrane , on the concentration of ammonia vapors, excitation by light with a wavelength of 405 nm.

Figure 5. Dependence of the relative luminescence intensity of CdSe / ZnS quantum dots embedded in the polymer track membrane sample on the number of the sorption / desorption cycle of ammonia molecules on their surface.

Example.

To demonstrate the operability of the proposed sensor, brightly luminescent hydrophobic CdSe / ZnS semiconductor quantum dots with a core diameter of 2.5 nm synthesized according to the high-temperature organometallic synthesis procedure described in (V.O. Dabbousi, J. Rodriguez-Viejo, FV Mikulec, JR Heine, H Mattoussi, R. Ober, KF Jensen, and MG Bawendi: (CdSe) ZnS Core-Shell Quantum Dots: Synthesis and Characterization of a Size Series of Highly Luminescent Nanocrystallites // J. Phys. Chem. B, 1997, 101 (46 ), pp.9463-9475) [6], were introduced into the parietal layers of the pores of polyethylene terephthalate track membranes with through cylindrical pores with a diameter of 0.5 μm (FLAR JINR, Dubna, Russia). A schematic representation of a membrane sample with embedded quantum dots is shown in FIG. 1. For this, membrane samples were impregnated with a solution of quantum dots in toluene according to the procedure described in (A.O. Orlova, Yu. A. Gromova, A.V. Savelyeva, VG Maslov, MV Artemyev, A. Prudnikau, AV Fedorov and AV Baranov. Track membranes with embedded semiconductor nanocrystals: structural and optical examinations. Nanotechnology. 22 (2011) 455201 (7pp)) [7].

To study the effect of ammonia vapors on the spectral properties of quantum dots embedded in polyethylene terephthalate track membranes, membrane samples were placed in a sealed chamber to which a controlled supply of air containing ammonia vapors was provided. Figure 2 shows a schematic illustration of a chamber for the controlled supply / pumping of ammonia vapor. A sample of the membrane 1 with embedded quantum dots is placed in a sealed chamber 2, which is connected to the chamber 4. In the chamber 4 through the hole closed by the stopper 5, is placed an aqueous solution of ammonia. After the equilibrium concentration of ammonia vapors is established in chamber 4, the valve 3 opens and chamber 2 is filled with ammonia vapors of a certain concentration. A membrane sample with embedded quantum dots is held in ammonia vapor for a fixed time (for example, for 2 minutes). After this, the sample is removed and its luminescent response is recorded.

Figure 3 shows the absorption and luminescence spectra of a sample of a polyethylene terephthalate membrane with embedded semiconductor quantum dots before and after the interaction of the sample with ammonia vapor.

Incubation of the sample membrane for 2 minutes in a sealed chamber filled with ammonia vapors _{(ammonia vapors} C = 13 million ^-1) leads to a decrease of the luminescence intensity of the quantum dots is 60%. A decrease in the luminescence of quantum dots is accompanied by a decrease in their luminescence decay time. This indicates the adsorption of ammonia molecules on the surface of quantum dots embedded in a polyethylene terephthalate track membrane. It should be noted that the interaction of the sample with ammonia vapors does not lead to a change in the absorption spectrum of quantum dots embedded in the sample (see Fig. 3, inset).

To determine the dynamic range of the concentration of ammonia vapors in air, in which a sample of a polymer track membrane with embedded quantum dots can be used as a sensor element for ammonia vapors, the membrane samples were kept for 2 minutes in chamber 2, in which a certain ammonia vapor pressure was created. It was found that increasing the concentration of ammonia in the vapor chamber from 0 to 20 million ^-1 results in a linear decrease of the luminescence intensity of the quantum dots embedded in a polymer track membrane. Figure 4 shows the dependence of the degree of quenching of the luminescence of quantum dots embedded in samples of polymer membranes on the concentration of ammonia vapor.

To reuse a polyethylene terephthalate track membrane with embedded CdSe / ZnS quantum dots as a sensor element, it is necessary after desorption of the sample with ammonia vapors to desorb it from the surface of quantum dots. For this, we used the installation shown in Figure 2. The membrane sample 1, which reacted with ammonia vapors, was placed in chamber 2, and a vacuum pump was connected to the tube with valve 7. Pumping out air led to a decrease in air pressure in chamber 2 and, as a result, to desorption of ammonia molecules from the surface of quantum dots embedded in a sample of a polymer membrane. It should be noted that, at the same time, the luminescence response of the sample was restored to the initial level, which was accompanied by an increase in the decay time of the luminescence of quantum dots embedded in the sample.

To study the possibility of reusing a sample of a polyethylene terephthalate track membrane with embedded CdSe / ZnS quantum dots as a sensor element on ammonia pairs, a complete sorption / desorption cycle of ammonia molecules on the surface of quantum dots embedded in the sample was performed 8 times. Figure 5 shows the luminescence intensity of the polymer sample track membrane with embedded CdSe / ZnS quantum dots, depending on the presence or absence of ammonia vapors _{(ammonia vapor} ^-1 = 13 million) in the chamber 1 (see FIG. 2). We found that an eightfold repetition of the complete sorption / desorption cycle of ammonia molecules on the surface of quantum dots embedded in a sample does not lead to any noticeable change in their luminescence intensity at each stage of the cycle. This indicates a high reproducibility of the response of the sample to the presence of ammonia vapors, to the high stability of quantum dots embedded in the polymer track membrane, and, as a consequence, to the possibility of multiple use of our sample as a sensor element on ammonia vapors.

Thus, the tasks of increasing sensitivity, the accuracy of determining the concentration of ammonia vapor, the life of the device and simplifying the manufacture of the sensor are solved.

Information sources

1. US patent No. 5252292, IPC G01N 27/04, application 524562, publication date 10/12/1993, priority date 05/17/1990).

2. US patent No. 3649505, 5 IPC G01N 27/30, application 803781, publication date 02/14/1972, priority date 03/03/1969.

3. US patent No.US 6406669 B1, IPC G01N 27/77, application 09/760121, publication date 06/18/2002, priority date 01/12/2001

4. US patent No.US 2003/0113932 A1, IPC G01N 21/77, application 10 / 024,670, publication date 06/19/2003, priority date 12/14/2001.

5. US patent No. 6013529, IPC G01N 33/00, application 08 / 906,711, publication date 11/01/2000, priority date 05/08/1997.

6. V.O. Dabbousi, J. Rodriguez-Viejo, F.V. Mikulec, J.R. Heine, H. Mattoussi, R. Ober, K.F. Jensen, and M.G. Bawendi: (CdSe) ZnS Core-Shell Quantum Dots: Synthesis and Characterization of a Size Series of Highly Luminescent Nanocrystallites // J. Phys. Chem. B, 1997, 101 (46), pp. 9463-9475.

7. A.O. Orlova, Yu. A. Gromova, A.V. Savelyeva, V.G. Maslov, M.V. Artemyev, A. Prudnikau, A.V. Fedorov and A V Baranov. Track membranes with embedded semiconductor nanocrystals: structural and optical examinations. Nanotechnology. 22 (2011) 455201 (7pp).

Claims (1)

A luminescent sensor for ammonia vapors in the atmosphere or in an air sample, consisting of a hydrophobic polymer membrane with a fluorophore, characterized in that the polymer membrane has through pores of nanometer or micron diameter, while the fluorophore is embedded in the parietal layer of through pores, and bright fluorescent is used as a fluorophore semiconductor quantum dots whose luminescence intensity changes when ammonia molecules bind to the surface of quantum dots.

Images