EP2561009A2 - Procédé de formation d'une nanostructure monodimensionnelle et nanostructure formée par le procédé - Google Patents

Procédé de formation d'une nanostructure monodimensionnelle et nanostructure formée par le procédé

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Publication number
EP2561009A2
EP2561009A2 EP11720831A EP11720831A EP2561009A2 EP 2561009 A2 EP2561009 A2 EP 2561009A2 EP 11720831 A EP11720831 A EP 11720831A EP 11720831 A EP11720831 A EP 11720831A EP 2561009 A2 EP2561009 A2 EP 2561009A2
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Prior art keywords
solution
dendrimers
nanostructure
nanofibers
metal
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EP11720831A
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German (de)
English (en)
Inventor
Amir Fahmi
Nabil Gindy
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IRIN LLP
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IRIN LLP
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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G83/00—Macromolecular compounds not provided for in groups C08G2/00 - C08G81/00
    • C08G83/008—Supramolecular polymers
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G83/00—Macromolecular compounds not provided for in groups C08G2/00 - C08G81/00
    • C08G83/002—Dendritic macromolecules

Definitions

  • This invention relates to a method of forming a one dimensional nanostructure or one dimensional hybrid nanostructure.
  • it relates to a method of forming an amine terminated dendrimers based one dimensional nanostructure and a method of forming a one dimensional nanostructure in aqueous solution. It also relates to such a one dimensional nanostructure. It also relates to a metallic species sensing substance. Further, it relates to a sensing substance for determining pH.
  • Nanofabrication is the construction of nanometre scale structures.
  • Self assembly is one method of nanofabrication in which a system is manipulated such that the components therein form the desired structure.
  • This invention is primarily related to a method of creating a series of conditions for the self assembly of one dimensional well-defined nano structures or nanofibres.
  • two dimensional and three dimensional structures can be formed from the nanofibres.
  • Dendrimers are globular macromolecules composed of a core, dendrons and surface groups. It has been found that dendrimers are useful for forming nano- objects.
  • Nanostructures based on multifunctional dendrimer-hybrid materials in aqueous media are particularly advantageous. Such nano structures are expected to show potential in wide range of applications from nanoelectronic, photoelectronic toward biotechnology and life-science. Nanofabrication via directed self-assembly of hybrid material into well-defined nano structures is a versatile and powerful tool for manufacturing the next generation of miniaturized devices. It is an object of the invention to provide a technique for mass fabrication of (multi)-functional nanostructure hybrid materials based on inorganic nanocomponents prepared in-situ within organic macromolecules. Embodiments of the invention comprise simple hybrid systems to fabricate high aspect ratio nanofibers.
  • the molecular self-assembly of amino-terminated polypropylene imine (PPI) dendrimers into nanofibers is induced by complexing transition metal ions to the terminal amines groups of the dendrimers.
  • the results disclosed herein show the creation of a shape and charge asymmetry in the dendritic scaffold together with the metal-ligand interactions to form uniform hybrid nanofibers of inorganic nanocomponents within the dendritic matrix.
  • These hybrid nanofibers can be used as a scaffold to deposit different types of transition elements to form nanofiber alloys.
  • the obtained one dimensional nanofibers possess unique physical properties useful for miniaturised electronic and photoelectronic devices.
  • a cation such as a metal salt
  • the method provides a simple, cost-effective, manufacturing process that can be performed in-situ at room temperature in an aqueous medium.
  • the method is environmentally friendly and flexible and yields multifunctional nanostructures that are light in weight, have a high surface area and can be modified further to form metallic, bimetallic, nano-alloy, magnetic material with semiconductor hybrid and metallic with semiconductor hybrid nanofibres.
  • the method can be used for building hybrid nanofibers based alloys (CdSe/Au, CdS/Au etc) of inorganic ordered nanoparticles within the organic-dendritic scaffold; for fabricating different thickness of nanofibers with high aspect ratio.
  • the resultant organic-inorganic nanofibres can be used as a scaffold to deposit different types of inorganic nanoparticles.
  • the method can also be used in the fabrication of nanofibers based on alloys of different types of metals and semiconductors.
  • the solution of dendrimers is an aqueous solution.
  • the solution may comprise dendrimers dissolved in an organic solvent.
  • the solvent is chosen depending on the type of dendrimer and the dendrimer's generation.
  • the dendrimers have two different families of functional groups, one functional group located in the core of each dendrimer molecule and the other functional group located at the terminus.
  • the dendrimers comprise amine terminated dendrimers.
  • the dendrimers comprise polypropylene imine (PPI) dendrimers or Polyamidoamine (PAMAM) dendrimers.
  • the dendrimers may have a generation between 0 and 7, preferably between 2 and 7. Most preferably, the dendrimers have a generation of 4 or 5.
  • the dendrimer solution has a concentration of between 0.1 mM and 1 mM and most preferably 0.3mM.
  • concentration may be dependent on the generation of the dendrimer.
  • the method may include a step of attaining a pH of the solution of dendrimers of between 9 and 7.
  • the method may include a step of reducing the pH of the solution of dendrimers to below pH 9 and most preferably to approximately pH 8.3. This is advantageous as the dendrimer solution typically has a pH of approximately 10.3 and with the reduction of pH the dendrimer surface becomes positively charged which advantageously affects the configuration and conformation of the dendrimers and promotes nanofiber formation.
  • the type of metal salt is selected such that the step of adding the metal salt attains a predetermined pH.
  • the metal salt is inorganic and may comprises a Cadmium salt and, in particular, Cadmium Acetate or Cadmium Nitrate.
  • the metal salt may be a Zinc salt, a Palladium salt, a Silver Salt or other transition metal salt. This is advantageous as the method can be used to control the assembly of many types of functional inorganic nanoparticles such as Cadmium or Zinc into well-defined I D and 2D-nanostructures via directed self-assembly of the dendrimers units.
  • the unidirectional self-assembly through the Cd(II)-bridging is believed to be a consequence of the relative flexibility of the dendritic scaffold which controls the shape and charge asymmetry.
  • the molar ratio of metal salt and dendrimers is greater than 5 : 1. Most preferably the molar ratio of metal salt and dendrimers is substantially 10: 1.
  • the method may include a further step of metallisation of the I D nanostructure; or a further step of introducing a semiconductor into the I D nanostructure to form a nanostructure incorporating a quantum dot; or a further step of introducing a semiconductor into the I D nanostructure and metallisation.
  • the method may include the steps of;
  • the metal precursor comprises a Gold precursor, which may comprise Chloroauric acid.
  • the molar ratio of dendrimer to metal precursor may be between 1 : 1 and 1 :7 and preferably is substantially 1 :3.
  • the step of reducing the metal of the metal precursor comprises the addition of a reducing agent which may comprise Sodium borohydride (NaBH 4 ).
  • a reducing agent which may comprise Sodium borohydride (NaBH 4 ).
  • the method may include the steps of; c) adding a semiconductor precursor such that the metal linked nanostructure and semiconductor precursor react together to form semiconductor nanoparticles.
  • the semiconductor precursor comprises one of Sodium hydrogen Selenide (NaHSe), Sulphur dichloride (SCI 2 ), Sodium sulfide (Na 2 S) and Sodium Telluride (Na 2 Te).
  • NaHSe Sodium hydrogen Selenide
  • SCI 2 Sulphur dichloride
  • Na 2 S Sodium sulfide
  • Na 2 Te Sodium Telluride
  • the metal salt comprises a Cadmium salt
  • these precursors can be used to prepare fluorescent CdSe or CdS or CdTe quantum dots within the nanostructure.
  • the Cd(II) precursor is further modified to incorporate fluorescent CdSe, CdS, CdTe quantum dots.
  • the optical properties of these nanofibers are not only sensitive to the particle size and shape, but also to their spatial distribution and the chemical environment.
  • the method may include the step of metallisation, comprising;
  • Self-assembled nanofibers of dendrimer stabilised metal and semiconductor quantum dots in aqueous media could be used as labels or markers in biotechnological applications. Modification of the fibers' surface, e.g. via metallisation, yields multifunctional I D-nanostructures that extend the range of accessible applications.
  • the ability of dendrimers to act as a unimolecular micelles for the controlled synthesis and stabilisation of inorganic nanoparticles is not the only one of their outstanding features. Their large number of functional groups and the unique molecular architecture also give rise to a great diversity of self-assembled structures in both thin films and solutions.
  • One-dimensional nanostructures are anisotropic and often possessing unique physical properties.
  • the invention demonstrates the ability of amine-terminated dendrimers (e.g. PPI) to direct the self-assembly of inorganic nanoparticles into one-dimensional aggregates in solution. It has been found that the decoration of the nanofibers with metallic gold nanoparticles leads to complete quenching of the fluorescence of a nanostructure having CdSe quantum dots incorporated therein. Thus, the nano structures can be used as sensors to determine the presence of metallic species.
  • PPI amine-terminated dendrimers
  • the method includes the step of forming 2D-nanostructures by applying an external field, such as electric or magnetic field, to direct the assembly of the one dimensional nanostructures into a two dimensional structure.
  • an external field such as electric or magnetic field
  • This is advantageous as electrically charged nanoparticles or magnetic nanoparticles within the nanofibers can interact with an electric field or a magnetic field respectively and can therefore be aligned according to the field direction and shape.
  • a second aspect of the invention we provide a one dimensional nanostructure formed in solution by the method of the first aspect of the invention.
  • a sensor for detecting the presence of metallic species in solution comprising a one dimensional nanostructure, said nanostructure having semiconductor quantum dots incorporated into its structure.
  • the nanofibres can also be used to detect temperatures changes, pH changes and ionic strength changes.
  • the metal species detector comprises a one dimensional nanostructure in aqueous solution having CdSe, CdS or CdTe quantum dots integrated into its structure.
  • the one dimensional nanostructure may comprise a plurality of dendrimers linked together with the quantum dots to form the one dimensional nanostructure.
  • the one dimensional nanostructure may be assembled into a 2D structure.
  • the senor comprises a nanostructure having semiconductor quantum dots formed by the method of the first aspect of the invention.
  • a fourth aspect of the invention we provide a method of altering the absorption/transmission spectra of a quantum dot, said quantum dot incorporated into the structure of a one dimensional nanostructure, the method comprising the steps of;
  • a metal containing substance such as a metal salt
  • quantum dot nanofibers can be modified such that the spectra changes and these changes utilised to produce labels or markers in biotechnology applications or detectors or other electro-chemical devices.
  • the one dimensional nanostructure comprises a structure described in relation to the first aspect of the invention.
  • the method includes the step of determining the type of metal species by analysing the spectra of the quantum dot.
  • a pH sensor for detecting the pH of a solution comprising a one dimensional nanostructure, said nanostructure having semiconductor quantum dots incorporated into its structure.
  • This pH sensor is advantageous as the spectra of the quantum dots can be monitored to determine the integrity of the nanostructure that incorporates the quantum dots. As the pH increases and decreases from around 8 to 10, the nanostructure disassembles with an associated reduction in the intensity of the spectra obtained from the quantum dots.
  • a seventh aspect of the invention we provide a method of determining changes in the pH of a test solution comprising the steps of;
  • nanostructure having at least one semiconductor quantum dot incorporated into its structure
  • I D one dimensional nano structures
  • 2D two dimensional
  • a well-defined one dimensional and two dimensional nano structures based on inorganic nano-particles prepared in-situ within the organic polymeric matrix.
  • a simple synthesis method of nanofibers comprising a one pot reaction at room temperature.
  • we provide accessibility to self assembly tool box consisting of a range of hybrid nano-objects to fabricate functional 2D-nanostructures.
  • nanofibers comprising both metallic, magnetic and semiconductors for unique electronic, optoelectronic and photoelectronic properties.
  • we provide a method of nano-alloy fabrication including metallic, bimetallic, semiconductors, magnetic, semiconductors-metallic, semiconductors coating with metallic layers, and semiconductors coated with magnetic layers.
  • a hybrid material based on different generation of dendrimers possessing key characteristic of donor-acceptor, gluco- dendrimers, Azo-dendrimers, hyper-branch dendrimers for many applications such as solar cell, nano-electronic, catalyst, biotechnology, optoelectronic, optics nanofibers, Photovoltaics, optics, Flexible electronics, MEMs, NEMs, Nanotechnology and High tech-devices.
  • Figure 1 shows a schematic illustration of dendrimer conformation and self-assembly, (a) molecular structure of 4 th generation polympropylene imine (PPI) dendrimers, (b) dendrimer conformation in aqueous media as a function of pH and the addition of a metal salt, (c) cation-induced, unidirectional self- assembly of dendrimer molecules into nanofibers, (d) metallization of Cd- complexed PPI nanofibers with gold;
  • PPI polympropylene imine
  • FIG 2 shows an Atomic Force Microscope (AFM) topogram (a) and Transmission Electron Microscopy (TEM) micrographs (b, c) of self- assembled nanofibers of polypropylene imine (PPI) dendrimers in the presence of Cd(AcO) 2 .
  • the micrograph in (d) is a magnified view showing the enrichment of Cd(II) in the nanofibers;
  • Figure 3 shows an AFM topogram of nanofibers of PPI[G4]-Cd(AcO)2.
  • the nanofibers are decorated with gold nanoparticles, the molar ratio of PPI[G4] :Au is (a) 1 : 1 , (b) 1 :3.
  • the TEM micrograph (c) and HR-TEM micrograph (d) show a regular distribution of Au nanoparticles along the nanofiber contour;
  • Figure 4 shows an AFM topogram (a) and EFM phase image (b) of self-assembled nanofibers of PPI[G4]-CdSe.
  • the CdSe particles appear as dark spots in the TEM micrographs (c).
  • the presence o fringes in the HR- TEM micrographs (d) also suggest the existence of crystalline nanoparticles;
  • Figure 5 shows AFM topograms of nanofibers of (a, b) PPI[G4]- Cd(AcO) 2 and (c, d) PPI[G4]-CdSe.
  • aThe nanofibers are decorated with gold nanoparticles, the molar ratio of PPI[G4] :Au is (a) 1 : 1 , (b) 1 :3 , (c) 1 : 1 and (d) 1 :7 respectively;
  • Figure 6 shows TEM micrographs of nanofibers of PPI[G4]-CdSe.
  • the insets in (a) and (c) are high resolution micrographs, (d) Histograms of the particle size distribution for both the CdSe and the Au nanoparticles.;
  • Figure 7 shows UV-Vis and photoluminescence (PL) spectra of (a) nanofibers of G4 dendrimer-stabilised CdSe quantum dots and (b) the same nanofibers after metallisation with Au.
  • the insets are optical photographs of aqueous solutions of nanofibers taken under UV-illumination;
  • Figure 8 shows AFM topograms of self-assembled nanofibers of (a) G2 and (b) G3 dendrimers with (- 1) Cd(AcO) 2 and (-2) CdSe particles;
  • Figure 9 shows AFM topograms of self-assembled nanofibres of (a) G4 and (b) G5 dendrimers with (- 1) Cd(AcO) 2 and (-2) CdSe particles;
  • Figure 10 shows a flow chart illustrating the method of producing the nanostructures
  • Figure 11 shows a flow chart illustrating the use of the quantum dot nanostructure as a pH detector and a metal species detector.
  • Figures 1 and 10 show a first embodiment of a method of forming a one dimensional nanostructure comprising a nanofiber.
  • One-dimensional nanostructures such as nanofibers are anisotropic and often possess unique physical properties.
  • Self-assembled nanofibers of dendrimer stabilised metal and semiconductor quantum dots in aqueous media could be used as labels or markers in biotechnological applications. Modification of the fiber surface, e.g. via metallisation, yields multifunctional one dimensional (ID) nanostructures that extend the range of accessible applications. It has been found that the number of repeating branches of a dendrimer (i.e.
  • the present embodiment utilises polypropylene imine (PPI) dendrimers in aqueous solution at a concentration of approximately 0.3 millimolar. It will be appreciated that other types of amine terminated dendrimers could be used.
  • the pH of the solution and the type of metal precursor has been found to affect the conformation and self-assembly of polypropylene imine (PPI) dendrimers, particularly of 2 nd to 5 th generation dendrimers.
  • aqueous dendrimer solution is shown in step 101.
  • the molecular structure of a 4 th generation amino-terminated PPI dendrimer is shown in Figure l a.
  • These dendrimers consist of an interior based on 30 tertiary amines and a periphery of 32 primary amines.
  • the conformation of amino-terminated PPI dendrimers has been found to be strongly dependent on factors such as the type of surrounding medium, its acidity and ionic strength.
  • Step 102 of Figure 10 comprises attaining a pH that promotes assembly of the dendrimers into nanofibers.
  • Figure lb shows, schematically, typical conformations of a 4 th generation amine terminated PPI dendrimer (G4) as the pH conditions are altered. It has been shown that PPI and Polyamidoamine (PAMAM) dendrimers at intermediate generations (i. e. 4 th and 5 th generations) are susceptible to conformational changes because the flexible dendrimer architecture allows back-folding of peripheral groups into the dendrimer's interior leading to a more globular shape.
  • PPI and Polyamidoamine (PAMAM) dendrimers at intermediate generations i. e. 4 th and 5 th generations
  • PAMAM Polyamidoamine
  • Figure l c and step 103 of Figure 10 show the addition of a metal salt to initiate self assembly of the dendrimers into fibers.
  • the step 102 may be achieved on addition of the metal salt to the solution thereby obviating the need for a separate pH adjustment step. If the metal salt is not introduced the conformational changes as a function of pH result in a topology of self-assembled dendrimer structures in thin film.
  • This step results in the formation of tens of micrometer long fibers with a diameter of just 4-6nm as shown in Figure 2a and step 104 of Figure 10.
  • a first indication of the fiber formation is that the dendrimer solution turns slightly opaque after the addition of the cadmium acetate. Dynamic light scattering experiments confirmed increase in hydrodynamic radius from 1.6nm for the unmodified PPI dendrimer to >500nm for the Cd(II)-complexed dendrimer nanofibers. This confirms that the fibers are already formed in aqueous solutions and not during film deposition.
  • nanofibers based on the mechanism proposed above relies on the presence of cations, which can act as a linker between the dendrimers. It has been found that the concentration of cations (Cd 2 ) is an important parameter that significantly affects the stability and size of the nanofibers.
  • concentration threshold of Cd(II) is dependent on the dendrimers' generation but in general a dendrimer to Cadmium(II) ratio of 1 : 10 is preferred for reliable nanofiber formation. If the ratio is 1 :20 then Cadmium ions have been found to be present in solution after the nanofibers have formed.
  • I D dendrimer aggregates relies on the presence of a charge and shape asymmetry in the Cd(II)-complexed dendrimer molecules.
  • the inventors studied the fiber formation as a function of dendrimer generation. Their results demonstrated that due to the higher flexibility of the dendritic scaffold at intermediate generations (G4 - G5) nanofibers of up to a micrometer long can be formed, while at lower generations fewer and shorter fibers are achieved.
  • Nanofibres having metallic Cadmium can be formed by a reduction step, however, alternative nanofibres can be formed as described below. It has been found that metal or semiconductor nanoparticles can be easily deposited through an extra wet-chemistry step to form bimetallic nanofibers (nanofibers based on nano-alloys) and nanofibres including semiconductors that are well aligned with the nanofibers, as will be described in more detail below.
  • FIG l e and step 105 of Figure 10 shows the metallisation of Cd(II)-complexed PPI dendrimer nanofibers.
  • Figure l e shows a method step of populating the nanofiber with nanoparticles of gold (Au).
  • Au gold
  • This method of creating bimetal nanofibres bypasses step I d shown in Figure 1 and proceeds directly from the step shown in Figure l c to the step shown in Figure l e.
  • a gold precursor of Chloroauric acid (HAuC ) is added to an aqueous solution of the Cadmium complexed nanofibers.
  • the aqueous solution is dilute to a dendrimer water ratio of 1 : 10.
  • the ratio of 4 th generation PPI to Chloroauric acid (PPI [G4] :HAuCLi) is preferably of a molar ratio between 1 : 1 and 1 : 3.
  • the gold precursor coordinates selectively to the terminal primary amines of the PPI dendrimers.
  • the gold is then reduced as shown in step 106.
  • gold nanoparticles are obtained which follow the contour of the nanofibers.
  • the Cd(II)-complexed PPI nanofibers can be used as scaffold for Au nanoparticles to obtain one-dimensional particle assemblies.
  • the reducing agent used in this embodiment is Sodium borohydride (NaBH 4 ) in solution.
  • the AFM topograms in Figure 3 a and 3b show metallised nanofibers of PP1[G4] - Cd(AcO)2, where necklace-like structures of Au nanoparticles are obtained, which mimic the contour of the nanofibers.
  • the gold nanoparticles are discrete and spaced from one another along the nano-fibers.
  • the gold precursor (HAuCLi) coordinates to the available remaining primary amine groups at the dendrimer periphery to obtain Au-nanoparticles after the chemical reduction with NaBH 4 in solution or after spin-coating on the substrate.
  • the nucleation and growth of the Au particles has been found to be governed by the kinetics of both the coordination of HAuCLi to the primary amines of PPI[G4] and the reduction of the gold precursor to metallic gold.
  • the degree of metallisation can be adjusted through the molar ratio of PPI [G4] :HAuCLi.
  • a higher density of Au particles decorating the nanofibers is achieved at higher concentrations of gold precursor.
  • only few Au nanoparticles are formed at molar ratios of PPI [G4] 1 : 1 as shown in Figure3a.
  • regular necklace-structures of nanofibers decorated with Au particles can be obtained at PPI[G4] 1 :3 as shown in Figure3b.
  • the spacing of the Au nanoparticles that is achieved by the above method appears to be relatively constant along the nanofibers with a narrow size distribution. No additional stabiliser was employed during the preparation.
  • the average particle size, as determined from TEM measurements ( Figure3-c), is 5.4nm with a standard deviation of 0.9nm. Moreover, the presence of fringes in the HR-TEM micrograph ( Figure3-d) suggests that the particles are crystalline.
  • the inventors believe that the low polydispersity and constant spacing of the Au nanoparticles can be understood considering their formation. As the gold precursor coordinates to available primary amines at the dendrimer surface a large number of gold particles are nucleated upon chemical reduction. Subsequently, the particles grow via coalescence of gold clusters, presumably in the fashion of an Ostwald ripening mechanism.
  • a narrow particle size distribution can be obtained, since the mobility of the initial Au clusters along the nanofibers is limited by the adsorption of Au clusters to the primary amines of the dendrimers. Hence, the particle growth is controlled and limited by the depletion of Au clusters in the vicinity of a growing particle. Assuming that the concentration of gold precursor at the nanofibers surface is consistent through a uniform charge distribution along the nanofibers, this leads to guide the nucleation mechanism to grow the Au-nanoparticles in a controlled manner toward low polydispersity and regular spacing.
  • Figure 3 also suggests that there are no free dendrimers present in the solutions because the Au precursor would also coordinate to available primary amines of these dendrimers instead of the nanofibers. This in return would lead to spherical molecules comprising single dendrimers associated with the gold particles that do not follow the contour of the nanofibers.
  • metallisation of Cd(II)- complexed nanofibers at intermediate Cd-concentrations (PPI[G4] :Cd(II) > 3 has been found to lead to uniform metallised nanofibers, which exceed several micrometers in length.
  • the above described self-assembly process is simple and flexible and the specific organic-inorganic interactions have been found to facilitate the formation of defect free well-defined I D-structures. These I D structures have potential uses in electronic applications and molecular biology.
  • a semiconductor precursor can be added to the solution to prepare a semiconductor nanofiber as shown in step 107 of Figure 10.
  • the semiconductor precursors may be Selenium based, Sulphur based or Tellurium based.
  • semiconductor precursors such as Sodium Selenide (NaHSe), Sulphur dichloride (SCI 2 ) and Sodium Telluride (Na 2 Te) can be used to prepare fluorescent CdSe/CdS/CdTe quantum dots within the dendrimers aggregates.
  • the resultant I D-structures have been found to be stable under the altered solution conditions, such that nanofibers with unique optical properties can be obtained.
  • the physical properties and micro structure of the nanofibers are characterised by means of Ultraviolet- Visible light (UV-Vis) and photoluminescence (PL) spectroscopy as well as Scanning Force Microscopy (SFM) and Transmission Electron Microscopy (TEM).
  • the initially colourless Cd(II) solution turns bright yellow signifying the formation of small CdSe nanoparticles with low Se content, as shown in Figure 4.
  • the optical properties of the CdSe quantum dots (QDs) were evaluated by means of UV-Vis and photo-luminescence (PL) spectroscopy; the results are presented in Figure 7.
  • the PPI[Cd(II)] nanofibers have been found to be stable during the synthesis of CdSe nanoparticles. Accordingly, this method achieves micrometer long nanofibers of CdSe nanofibers based on amine-terminated PPI dendrimers and CdSe nanoparticles.
  • the CdSe particles act as a linkage between adjacent dendrimer molecules.
  • the morphology of nanofibers containing CdSe nanoparticles are similar to the ones obtained in the presence of Cd(AcO)2 precursor. It has been found that in the case of a 4 th generation dendrimer based nanofiber including CdSe, the nanoparticles in the nanofibers have an average diameter of 6.4 nm and a length of up to 8 ⁇ (Figure 4a). The presence of the CdSe nanoparticles in the nanofibers is apparent in the electric force microscopy measurements, shown in Figure 4b, where the nanofibers containing nanoparticles yield a strong phase contrast. The cross section, shown in Figure 4b, also suggests a relatively constant spacing ( 1 lnm) between the nanoparticles.
  • Nanofibers are anisotropic and often possess unique physical properties such as ballistic electron transport and unusual optical characteristics. It is expected that modification of the surface of a semiconductor complexed nanofiber by metallisation with different types of metals (such as Au, Ni, Pd, Co, ) may lead to unusual physical properties that increase the range of accessible applications.
  • dendrimer nanofibres linked with Cadmium and Selenium (CdSe) are metallised with metallic gold (Au) nanoparticles.
  • Such fibres can be used as optoelectronic components, and also as a diagnostic agent using the strong fluorescence in the fibers which could hold Antigens or antibodies for detection.
  • the semiconductor nanofibres are created using the method described above to achieve the CdSe joined dendrimer fibres shown in Figure I d.
  • a gold precursor of Chloroauric acid (HAuCL t ) is added (step 109) to dilute aqueous solutions of the nanofibers (PPI[G4]-Cd(AcO) 2 and PPI[G4] -CdSe) in a certain molar ratio. It has been found that a molar ratio of PPI[G4] :HAuCLi of 1 : 1 to 1 :3 is preferable.
  • the gold precursor coordinates selectively to the terminal primary amines of the PPI dendrimers.
  • nanofibers incorporating CdSe Quantum Dots can be used to template Au nanoparticles and direct their spatial order into one-dimensional assemblies.
  • the AFM topograms in Figure 5 show metallised nanofibers of PPI[G4]- Cd(AcO) 2 and PPI[G4] -CdSe respectively. It has been found that the metallisation of nanofibers can be successfully achieved with Cd(II) or CdSe containing nanofibers. In either case, necklace-like structures of Au nanoparticles are obtained, which mimic the contour of the nanofibers as shown in Figure 3. It has been found that the addition of a reducing agent, such as NaBH 4 , is not always necessary although it is shown as step 1 10 in Figure 10.
  • a reducing agent such as NaBH 4
  • the gold precursor is reduced practically instantaneously when added to the PPI[G4]- CdSe nanofibers ( Figure 5c, d), due to residual NaBH 4 , which had been added to the solution during the synthesis of CdSe nanoparticles.
  • the degree of metallisation can be adjusted through the molar ratio of PPI[G4] :HAuCLi; a higher density of Au particles decorating the nanofibers can be achieved if more gold precursor is added to the nanofiber solutions.
  • a higher density of Au particles decorating the nanofibers can be achieved if more gold precursor is added to the nanofiber solutions.
  • the inventors found that the nanofiber morphology is perturbed at high concentrations of gold precursor (PPI[G4] :HAuCl 4 ⁇ 1 :7), especially for PPI[G4]-Cd(AcO) 2 nanofibers. It is suspected that the addition of high concentrations of Chloroauric acid (HAuCLi) decreases the solution pH and shifts the balance between attractive and repulsive interactions among the dendrimers.
  • HAuCLi Chloroauric acid
  • the higher degree of protonation of primary amines (NH 3 + ) at the dendrimer surface and tertiary interior amines enhances the coulomb repulsion and may lead to the disassembly of nanofibers and the formation of cadmium-complexed PPI[G4] dendrimer structural units.
  • the spacing of the Au nanoparticles appears to be relatively constant along the nanofibers. Moreover, the Au particles show a narrow size distribution, when no additional stabiliser was added during their preparation process. The average particle size determined from TEM measurements is found to be around l Onm with a standard deviation of 1.8nm.
  • Nanofibers of PPI[G4]-CdSe show fluorescent properties with a strong emission band at as shown in Figure 7a.
  • the position of the emission band of semiconductor quantum dots depends not only on the particle size and composition but also the state of their surface and the surrounding medium.
  • Figure 1 1 shows a method of using this effect to detect the presence of a metal species.
  • Step 1 1 1 shows the provision of a nanofibre having quantum dots in its structure.
  • Step 1 12 shows the introduction of a solution to be tested.
  • Step 1 13 shows the step of observing spectra changes of the quantum dots to determine the presence of metal species.
  • Step 1 1 1 shows the provision of a nanofibre having quantum dots in its structure.
  • Step 1 12 shows the introduction of a solution to be tested.
  • Step 1 13 shows the step of observing spectra changes of the quantum dots to determine the changes in the pH, which can cause disassembly of the nanofibers.
  • the nanofiber diameter is lower for nanofibers with Cd(AcO)2 and increases upon Selenisation of the Cd(II) precursor to form CdSe nanoparticles. This effect is pronounced again for low dendrimer generations.
  • the nanofiber diameter is below 1.5nm ( Figure 8a) and increases to 4nm upon the formation of CdSe nanoparticles ( Figure 8a).
  • the nanofiber diameter increases from 1.7nm with Cd(AcO) 2 precursor to 5.4nm with CdSe nanoparticles.
  • the diameter gain is due to the growth of CdSe nanoparticles, which are larger than the radius of gyration of the pristine dendrimers. Since the particle diameter is only weakly dependent on the dendrimer generation, the final thickness of PPI-CdSe nanofibers is relatively constant around 6nm (Figure 9). For the high generation dendrimers (G4 and G5) we obtain nanofibers exceeding 4 ⁇ in length ( Figure 9). Again their diameter increases upon the formation of CdSe nanoparticles; however the diameter again is much lower compared to G2 and G3.
  • the present invention provides a simple bottom-up tool and versatile method to fabricate organic-inorganic nanofibers via directed self-assembly in aqueous solution.
  • the resulting hybrid nanofibers especially using 4 th and 5 th generation dendrimers, have been found to be stable for several weeks in aqueous solution at ambient temperature.
  • the method could be applied to other metals using an appropriate metal precursor.
  • an appropriate metal precursor for example, Silver, Platinum and Palladium metal precursors may be used.
  • the CdSe nanofibers have a positive charge and therefore negatively charged metal precursors such as AuCLf electrostatically interact with the CdSe nanofibers.
  • the method could be applied to other semiconductors using an appropriate semiconductor precursor.
  • an appropriate semiconductor precursor Na 2 S, SCI 2 or Na 2 Te.
  • thiol based dendrimers could be used.
  • the metal salt is preferably a gold based metal salt.

Abstract

La présente invention a pour objet un procédé de formation d'une nanostructure monodimensionnelle comprenant les étapes consistant : à fournir une solution de dendrimères de 4ème ou de 5ème génération ; à atteindre un pH sensiblement égal à 8,3 et à ajouter un sel métallique à la solution pour provoquer un auto-assemblage induit cationiquement des dendrimères en des nanostructures monodimensionnelles. La présente invention concerne aussi un capteur d'espèces métalliques, un capteur de pH et un procédé de modification des spectres d'une boîte quantique.
EP11720831A 2010-04-19 2011-04-19 Procédé de formation d'une nanostructure monodimensionnelle et nanostructure formée par le procédé Withdrawn EP2561009A2 (fr)

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GBGB1006520.9A GB201006520D0 (en) 2010-04-19 2010-04-19 Nano fabrication of hybrid materials
PCT/GB2011/050774 WO2011131979A2 (fr) 2010-04-19 2011-04-19 Procédé de formation d'une nanostructure monodimensionnelle et nanostructure formée par le procédé

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CN102703057A (zh) * 2012-05-18 2012-10-03 北京工商大学 一种聚酰胺-胺树形分子包覆的ZnX半导体量子点在指纹显现中的应用
JP6247289B2 (ja) 2012-06-29 2017-12-13 ノースイースタン ユニバーシティ ナノ要素の電界誘導組立てによって調製された３次元結晶性、均一および複合ナノ構造体
EP2881197A1 (fr) * 2013-12-03 2015-06-10 Nanogap Sub NM Powder, S.A. Procédé de préparation de nanoparticules métalliques anisotropes et agent destiné à réguler la croissance de celles-ci

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JASON M. CRISCIONE ET AL: "Self-assembly of pH-responsive fluorinated dendrimer-based particulates for drug delivery and noninvasive imaging", BIOMATERIALS, vol. 30, no. 23-24, 1 August 2009 (2009-08-01), pages 3946 - 3955, XP055154302, ISSN: 0142-9612, DOI: 10.1016/j.biomaterials.2009.04.014 *

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Publication number Priority date Publication date Assignee Title
CN113372564A (zh) * 2021-06-08 2021-09-10 安徽师范大学 由2,2’-联吡啶配位合成的金属配合物纳米线及其制备方法

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