DE10235182A1 - Preparation of semiconductor nanoparticles, useful e.g. for labeling biomolecules in medicine or biotechnology, uses an aromatic compound or metallocene as metal source - Google Patents

Abstract

Preparation of nanoparticles (NP), based on an organometallic compound or its derivatives, in which an aromatic organometallic compound or metallocene is used as metal source (A), is new. An Independent claim is also included for cadmium selenide and cadmium telluride NP produced by the new method.

Description

The invention relates to a novel Process for the production of nanoparticles based on organometallic Compounds and derivatives thereof.

The boundary area between molecular clusters and bulk crystals has been in the spotlight for some time now Interest. Through the targeted production of particles, layers and three-dimensional structures, with dimensions of 1 nm - 500 nm, materials are created with chemical and physical properties, that differ from those of macroscopic materials.

Semiconductor nanocrystallites with diameters from 1 nm - 5 nm emit absorbed light with an energy that is reversed is proportional to their diameter. This effect is on it attributed to that with increasing cluster size developed the well-known semiconductor band structure from molecular orbitals [1, 2, 3]. This phenomenon corresponds to this "quantum size effect" the energy of the emitted light of the band gap between the valence band and Conductor band of the semiconductor nanoparticle [4, 5]. The blur of the wavelength of the emitted photon depends on the diameter of the dispresity certainly. Not least because of the possible applications of this optoelectronic properties in diode construction or for labeling of biomolecules semiconductor nanocrystallites have become more important in recent years gained in current research [6, 7, 8, 9].

For the later commercial and industrial use of semiconductor nanoparticles it is necessary you reliable, in sufficient Yield and with defined properties, preferably monodisperse, to synthesize. Various synthesis routes have been proposed for this purpose, including sol-gel Processes [10], syntheses in the gas phase [11] and working with various Organometallic compounds [12, 13, 14].

Bawendi, Guyot-Sionnest and Alvisatos used for the synthesis of, for example, cadmium selenide nanoparticles System of elemental selenium and dimethyl cadmium in a trioctylphosphine / Trioctylphosphine Oxide Matrix (TOP / TOPO Matrix) for reaction at high temperatures under an inert atmosphere was brought [12, 13, 15].

The widespread synthesis of cadmium selenide nanoparticles using the Alvisatos method and Bawendi has some drawbacks due to the use of Dimethyl cadmium are due. Dimethyl cadmium (DMCd) is the first, but also the most unfavorable of all previously published cadmium sources. DMCd is difficult and only Manufacture in small quantities, violently explodes on contact with Water, or oxygen, is so unstable that it becomes during the Processing disintegrates and commercially unavailable is. This results in The synthesis has the disadvantages that it is only manageable in small quantities (otherwise the handling is too dangerous) and no reproducible synthesis is possible and that high reaction temperatures (> 300 ° C) necessary are. Cadmium-containing nanoparticles are not with this method reproducible with identical properties, which also on the different qualities of diverse batches of dimethyl cadmium could be attributed.

Peng and Peng presented a synthesis of cadmium selenide nanoparticles in which they used cadmium oxide as a cadmium source [16]. The high quality of the particles obtained in this way was attributed to the lower reactivity of cadmium oxide compared to dimethylcadmium, a resulting delay in nucleation and a lower injection temperature. The use of, for example, CdO or CdAc ₂ is advanta- geous over the use of dimethyl cadmium (it is, for example, less dangerous; at the same time the reaction is more controllable); however, there are still disadvantages because expensive additives are necessary and the reaction temperatures are still above 260 ° C, the soft point of Teflon.

This shows that the synthesis of Nanoparticles can only take place under extreme conditions, which in the Practice poor, uneconomical, inefficient and possibly also can only be handled under dangers. The general synthesis of II-VI nanoparticles runs usually so that a "coordinating" Medium is heated under protective gas and then a solution of Pre-reaction is injected. Alternatively, one can the reactants are presented. After the nucleation of nanoparticles there is a growth phase in which the particles reach the desired Grow in size be left (see e.g. [17]).

Based on this state of the art it is an object of the present invention, a possibility of economically effective synthesis of nanoparticles under mild To create conditions.

This task is characterized by the Features of claim 1 solved.

According to the invention are then used as a metal source aromatic organometallic compounds or metallocenes used. Naphtenates, e.g. Cadmium naphtenate, cobalt naphtenate or also zinc naphtenate.

The use of cadmium naphtenate as a cadmium source for the production of cadmium-containing nanoparticles is advantageous since, in contrast to dimethyl cadmium, cadmium naphtenate is not pyrophoric, resistant to atmospheric oxygen, and is easy to handle. Cadmium naphtenate is also inexpensive and can be used without additives, it is harmless and easy to handle, the synthesis can be precisely controlled. Another advantage arises from the fact that the reaction occurs at significantly lower temperatures Compared to the prior art, it runs below 260 ° C, which is important for large-scale synthesis because Teflon (part of many devices) softens from 260 ° C. This makes cadmium naphtenate as a cadmium source very suitable with regard to a later "scale up" of the synthesis. By using cadmium naphtenate as a cadmium source, the synthesis can be carried out reproducibly, defined, harmlessly and inexpensively.

The invention provides a possibility of substitution the usual as a cadmium source for the production of precursors using cadmium-containing nanoparticles created. This is how the nanoparticle synthesis is represented much easier and cheaper. Cadmium naphtenate is durable and long is constant against atmospheric oxygen and humidity. It is easy to handle and therefore enables also on an industrial scale scale the defined production of cadmium-containing nanoparticles under relative mild conditions, with monodisperse diameters and therefore exact adjustable emission wavelengths.

The same applies analogously to the production other metal nanoparticles, e.g. for the production of cadmium, Cobalt and zinc nanoparticles. Other naphthenates with other metals as a precursor are conceivable.

Depending on the growth temperature particles with specific wavelengths and at defined time intervals succeed synthesize. That means the lower the temperature is chosen, the longer is delayed the nucleation and the growth rate, so that the particles more time must be given until they reach certain sizes or: wavelength have grown. Choosing a higher reaction temperature leads to that germs form faster, that they grow faster and that desired Reach diameter faster.

It turns out that at a higher reaction temperature the particles are monodisperse with respect their diameter and thus the emission becomes sharper. The synthesis developed here offers a representation method of Cadmium-containing nanoparticles that make them easily, quickly and reliably accessible. Compared to other methods, it has the mildest yet and most reproducible conditions.

The nanoparticles produced in this way are suitable as a bully for biomolecules for example - but not exclusively - for peptides, Proteins, antibodies, nucleic acids or enzymes. Leave due to the photoluminescence of the nanoparticles themselves biomolecules mark with these nanoparticles ("label") and their attachment or Absence in biological systems highly in vivo or in vitro detect effectively. In this way, even a single nanoparticle can be detected become. They point in comparison to conventional marking methods for biomolecules, for example radioactive labels have advantages because of the use of such Markings due to regulatory Requirements for radioactive experiments are more complex and usually are also very expensive. In contrast to conventional ones Allow fluorescent labels the nanoparticles according to the invention a much more sensitive detection and are therefore also favors. equally the nanoparticles of the invention also used for marking in physico-chemical processes. In addition to the use in biotechnology, medicine, biochemistry also for use with phosphors, dyes, solar cells or numerous other electro-optical applications.

The size of the procedure produced nanoparticles varies and results from the germ or Growth rate, which in turn depends on the reaction temperature dependent is. The growing time that begins after nucleation depends on the growth temperature and can last from seconds to days. Usually the growth temperature is chosen so that the particle growth is completed in a few minutes to a few hours. preferred Diameters of the nanoparticles are between 0.5 nm and 15-20 nm. Nanoparticles with a diameter of are particularly preferred 1 to 5 nm.

As the preferred reaction temperature has proven a temperature range between 60 ° C and 300 ° C, particularly preferred however between 150 ° C and 250 ° C.

Is done in this temperature range for example the preparation of nanoparticles with cadmium naphtenate. Usually a or several reaction precursors (e.g. selenium brought into solution) in one Temperature 10-30K above injected the growth temperature. The synthesis typically proceeds in a coordinating medium such as trioctylphosphine oxide (TOPO), Trioctylamine (TOA), hexadecylamine (HDA) or in other amines, Phosphine oxides, carboxylic acids etc.

The emission maxima of, for example Cadmium selenide nanoparticles synthesized in this way lie between 490 nm and 700 nm.

The method according to the invention is for production a variety of nanoparticles, not just the ones described Selenides, but also tellurides, e.g. Cadmiumtelluriden, but basically also for all so-called II-VI semiconductor nanoparticles such as CdS, CdSe, CdTe, ZnS etc. In the sense of the invention, alloys such as, for example, are also expressly used (but not exclusively) CdZnS, HgCdSe, MnZnO or similar as nanoparticles according to the invention considered.

Further advantageous measures are contained in the remaining subclaims. The invention is illustrated in the accompanying drawings and is also described below with the aid of examples and test runs hen described in more detail for parameter optimization. It shows:

1 Fluorescence spectra of cadmium selenide nanoparticles. Under the same conditions regarding reaction time (five minutes) and reaction temperature (250 ° C) and various injection temperatures.

2 Reaction temperature dependence of the maximum emission position of the formed cadmium selenide nanoparticles.

3 Relationship between particle diameter and temperature at which they are formed.

4 Transelectron microscopy images of cadmium selenide nanoparticles that were formed at different reaction temperatures. a 180 ° C, b 200 ° C, c 220 ° C, d 250 ° C.

5 Dependence of the emission maxima of cadmium selenide nanoparticles on the reaction time at constant reaction temperature (250 ° C).

6 Direct dependence of the emission maxima of the cadmium selenide nanoparticles on the reaction time.

7 Dependence of the formation of cadmium selenide nanoparticles on time at a reduced reaction temperature (220 ° C).

embodiment

261 mg cadmium naphtenate ( 17 .2%) (corresponds to 0.4 mmol cadmium) are made up to 4 g total weight with trioctylphosphine oxide (TOPO). This mixture is heated to 200 ° C. in a Schlenk flask with constant evacuation and re-venting under N ₂ . The solution is then heated in an inert atmosphere to the desired injection temperature (e.g. 250 ° C). At this temperature, 41 mg (0.51 mmol) of selenium dissolved in 2.4 ml (trioctylphosphine) TOP are injected. The reaction mixture is allowed to cool to the desired growth temperature (e.g. 220 ° C). The reaction mixture is stirred at this temperature until the particles have reached the desired size (for example about 5 min for 3 nm). Then allowed to cool to 80 ° C and the resulting nanoparticles are precipitated with dry methanol. The particles are centrifuged, washed with methanol and redispersed in CHCl ₃ . The cadmium selenide nanoparticles obtained in this way are characterized by means of fluorescence spectroscopy and transelectron microscopy (TEM).

The yields of such preparations depend entirely on the chosen synthesis parameters. The nanoparticles according to the invention are formed as nuclei from the educts, the educts being gradually consumed; for example (for illustration):

The yield depends on the desired one Particle size. in the The optimization of the synthesis parameters is described below. The advantages of the invention also result directly from the optimization recognizable:

1. First, the influence of the temperature at which the selenium is introduced into the reaction solution on the physical properties of the particles obtained from it was investigated. For this purpose, the selenium dissolved in TOP was injected at temperatures of 250 ° C, 270 ° C, 275 ° C and 300 ° C to the cadmium naphtenate / TOPO mixture. In four experiments, the reaction temperature was kept constant at 250 ° C. for five minutes after the injection. The particles were then isolated, cleaned and analyzed by means of fluorescence spectroscopy and transelectron microscopy (TEM). 1 shows the fluorescence spectra of four samples. The emission maxima of all four samples are 590 nm. The in 1 The slight deviations that can be identified are not related to the respective injection temperature. The average diameter of the nanoparticles in the TEM was 3.54 nm.

2. Since no relationship between the temperature at which the selenium solution is added to the reaction and the average diameter or the physical properties of the nanoparticles, which depend on the diameter, could be derived from these findings, nor did the properties of the particles investigated depend on the Injection temperature of the second educt was found, the influence of the reaction temperature on the formation of the particles was examined. In a series of experiments, the selenium solution was added to the cadmium source cadmium naphtenate at 250 ° C. The reaction was then given five minutes at 180 ° C, 200 ° C, 220 ° C and 250 ° C to establish. The particles were then precipitated, washed and also examined using fluorescence spectroscopy and TEM. In 2 the spectra of four samples are shown. It is the emission wavelengths against the relative In intensities applied. A red shift in the emission maxima can be seen with increasing reaction temperature. The maximum of the particles that were created at 180 ° C is lowest at 520 nm. The particles formed at 200 ° C and 220 ° C each show a maximum in the emission at wavelengths of 537 nm and 560 nm. The particles which were obtained from the reaction at 250 ° C emit most red-shifted at 579 nm. It is striking that the higher the reaction temperature, the better the quality of the particles in terms of their monodispersity. The particles obtained at 180 ° C and 200 ° C show a broad band with hardly any intensity. While the spectra of the particles grown at 200 ° C and 250 ° C with half-widths of approx. 39 nm are very sharp-banded with regard to their emission. This observation suggests a nucleation delay that depends on the reaction temperature. In 3 the reaction temperature is plotted against the average particle diameter. This results in an almost linear relationship between the temperature and the diameter and thus the emission maximum. The TEM recordings in 4 show the particles obtained at the respective reaction temperatures. This is how the particles with the average diameters can be 2 .09 nm ( 4 a) and 2.79 nm ( 4 b) assign the reactions to 180 ° C and 200 ° C. The particles with the average diameters 3 .39 nm ( 4 c) and 3.79 nm ( 4 d) were obtained from the reactions at 220 ° C and 250 ° C. 4 again illustrates the relationship between reaction temperature and diameter. From the test series it follows that the diameter and maximum emission of the particles in the synthetic system used can be set exactly by a suitable choice of the reaction temperature. A higher reaction temperature leads to particles with larger, monodisperse diameters and thus to a sharp-band emission. As a result, a combination of 250 ° C for the injection and 220 ° C for the reaction was a good basis for further experiments.

3. Since the formation reaction of the cadmium selenide nanoparticles depended on the reaction temperature, the influence of the reaction time was examined below. For this purpose, the cadmium naphtenate-TOPO mixture was heated to 250 ° C. and the selenium solution was added at this temperature. This mixture was stirred for one, two, five, ten and 30 minutes at a reaction temperature of 220 ° C. After the particles were isolated and cleaned, they were examined by fluorescence spectroscopy. In 5 the emission wavelengths are plotted against the relative intensities in the respective spectra. As expected, a red shift in the emission maxima can be seen with increasing reaction time. In the spectrum, which corresponds to a reaction time of one minute, no pronounced maximum can be seen, and no photoluminescent particles have formed. After a reaction time of two minutes, the spectrum shows a maximum at 542 nm with 75% intensity compared to the remaining maxima.

A reaction time of five minutes provides particles that emit at a maximum at 562 nm. Response times of ten and 30 minutes correspond to maximum layers of 584 nm and 598 nm in the respective spectrum. All four maxima show a half width of approximately 50 nm, although a half width of 35 nm could also be achieved. This indicates that the size distribution of the mean particle diameter is determined only by the reaction temperature and not by the reaction time. 6 plots the response time against the wavelength. A logarithmic dependence of the emission maxima on the reaction times can be seen. This figure clearly shows that longer reaction times result in a larger red shift in the emission maxima. It is clear that the properties of the resulting particles can be influenced over the reaction time.

7 shows the spectra of the particles obtained from another series of experiments. In this series, the selenium solution was added to the cadmium precursor at a temperature of 220 ° C and the mixture was then stirred at a temperature of 200 ° C for 2, 10 and 30 minutes. The figure shows that after 2 and 10 minutes no particles can be detected using fluorescence spectroscopy. After a reaction time of 30 minutes, particles were obtained which have an emission maximum at a wavelength of 571 nm. The maximum emission of these particles is thus 29 nm lower than that of the comparable ones from the previous test series. The comparison of the 5 and 7 highlights the influence of reaction time and reaction temperature on the investigated physical properties of the cadmium selenide nanoparticles. It can be seen that the position of the emission maximum of the synthesized particles depends directly on the reaction temperature and the reaction time and thus their properties can be influenced directly by the appropriate choice of the reaction conditions. It is striking that the synthesis with cadmium naphtenate did not produce any particles whose emission maximum was below 500 nm. 5 indicates that it is not possible with this method to display particles with a photoluminescence below 500 nm. After a one minute reaction time, no maximum was observed in the spectrum, after two minutes the maximum was already at 540 nm. The lowering of the reaction temperature further delayed the nucleation, so that no particles were formed after ten minutes.

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Claims (16)

Process for the production of nanoparticles based on organometallic compounds and derivatives thereof, characterized in that aromatic organometallic compounds or metallocenes are used as the metal source. A method according to claim 1, wherein as aromatic organometallic Compounds (precursor) metal naphtenates are used. The method of claim 2, wherein cadmium naphtenates, cobalt naphtenates or zinc naphtenates are preferred. Method according to one or more of the preceding claims, wherein according to this process, in particular II-VI semiconductor nanoparticles getting produced. Method according to one or more of the preceding claims, wherein Cadmium selenide nanoparticles are produced. A method according to claim 5, characterized in that as Selenium source in solution brought elemental selenium is used. Method according to one or more of the preceding claims, wherein the solvents selected are made of trioctylphosphine, trioctylphosphine oxide, hexadecylamine or other amines, phosphine oxides or carboxylic acids. Method according to one or more of the preceding claims, wherein the preferred reaction temperature for the production of the nanoparticles between 60 ° C and 300 ° C lies. The method of claim 8, wherein a temperature range is particularly preferred between 150 ° C and 250 ° C is. Method according to one or more of the preceding claims, wherein, the diameter of the nanoparticles preferably between 0.5 nm and is 20 nm. The method of claim 10, wherein! the diameter of the nanoparticles is particularly preferably between 1 and 5 nm. Method according to one or more of the preceding claims, wherein, the emission maxima of the synthesized nanoparticles between 490 nm and 700 nm are. Cadmium selenide nanoparticles made by the process according to claims 1 to 12th Cadmium telluride nanoparticles made by the process according to claims 1 to 12th The cadmium-containing nanoparticles according to claim 13 or 14, wherein the irradiation wavelengths to achieve a maximum emission between 380 nm and 450 nm lie. Use of the nanoparticles according to one or more of claims 1 to 15 as photoluminescent particles for labeling biomolecules.