DE102012100467B4 - Process for the preparation of a monolayer with hydrophilic ligand-coated nanoparticles and surface coated with this layer - Google Patents

Abstract

A process for producing a monolayer of nanoparticles containing hydrophilic, positively or negatively charged ligands selected from the group comprising the compounds of formula 1a, 1b or 1c: wherein Y is COO, SO 3 -, SO 4 -, HPO 3 -, PO 3 2- or Phenoxy anion or Y is in the form R1R2R3A + B-, wherein AN is P, B is an inorganic or organic anion, R1, R2, R3 are alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, cycloalkynyl, aryl, heteroaryl in which R1, R2, R3 can be joined together, X is S or Se, n is from 1 to 20, m is from 0 to 2, p is from 0 to 2, coated, the method being characterized in that the Monolayer of nanoparticles by vertical, relative to the monolayer, immersion or erosion of a substrate is applied to the surface thereof, and wherein previously a monolayer of nanoparticles in methanol / dichloromethane to the surface of the water He was applied and pressed together tightly on this surface using Langmuir-Blodgett technique.

Description

The invention relates to a method for producing a monolayer of nanoparticles which are coated with hydrophilic, positively or negatively charged ligands, a layer - and preferably - a monolayer of these nanoparticles and a surface coated with this layer, the layer having a like herein described method was prepared. The monolayers produced are u. a. used for coating materials such as glass, indium tin oxide (ITO), silicon and other semiconductors.

Nanoparticles are particles of elements and organic, inorganic or biological compounds in which, by convention, one of the dimensions is less than 100 nm. In the nanoparticles, physical phenomena and chemical properties occur which do not occur with less shredded substances. An example of this is an optical phenomenon of surface plasmon resonance (SPR) for noble metal nanoparticles. In addition, the nanoparticles are characterized in particular by the fact that their physical and chemical properties are size-dependent, such. B. decreasing melting temperature with decreasing size of gold nanoparticles. Some properties of the nanoparticles can be controlled by a coating with ligands, which protect mainly nanoparticles against aggregation. By selecting appropriate ligands, the properties of individual nanoparticles can be arbitrarily controlled. The above-mentioned specific properties of nano-sized matter open the way to the development of new nanoparticle-based materials and components. One of the materials most in demand today is thin films used in electronics, renewable energy sources, medicine and many other applications.

The development and fabrication of two-dimensional structures consisting of or containing metal or semiconductor nanoparticles is currently being explored in numerous studies [Shipway A.N., Katz E., Willner I. ChemPhys Chem., 2000, 1, 18-52]. The monolayers formed from nanoparticles have enormous application potential. The nanoparticle monolayers thin films are promising materials in the manufacture of LED displays, solar cells, capacitors, reflective and antireflective coatings, biological detectors and magnetic data carriers. Expanding the functionality of monolayer-based nanoparticle materials is another important step in the development and commercialization of these devices. The introduction of a permanent and well-defined electrical charge represents an interesting modification of the monolayers from a practical point of view. In addition to functionalities, the monolayers composed of electrically charged nanoparticles can serve as substrates that use electrostatic phenomena. A simple example of a possible use of such a monolayer is the development of a detector based on localized surface plasmon resonance (LSPR) or surface enhanced Raman scattering (SERS) for the detection of biological Objects or connections. The biological objects often have an electrical charge and can be electrostatically adsorbed on an oppositely charged nanoparticle monolayer.

At present, some methods of preparation of the charged nanoparticle monolayers are known. These methods utilize the electrostatic attraction of oppositely charged surfaces and nanoparticles. In this approach, the substrate surface to be coated is first modified by organic compounds with positive or negative charge. Subsequently, oppositely charged nanoparticles are adsorbed on the previously modified surface.

The patent application US 2008/0102201 A1 "Method for dispersing nanoparticles and methods for producing nanoparticle thin films by using the same" relates to a method for surface coating with charged nanoparticles by means of spin coating. In this method, a positively charged substrate surface and negatively charged palladium nanoparticles are used. The production of negatively charged nanoparticles is carried out by using a buffer solution with pH> 7. The production of a single nanoparticle layer is controlled by the pH change and the use of capillary forces.

One modification of the electrostatic attraction based process employs a hydroxy-coated surface, e.g. As a gold, silicon surface or the surface of another substance whose surface has been previously oxidized.

The patent application US 2009/0098366 A1 "Methods of coating surfaces with nanoparticles and nanoparticle coated surfaces" relates to a method for surface coating with oppositely charged Nanoparticles. The coating was made by immersing the substrates in a specially prepared electroneutral solution of oppositely charged gold, silver or palladium nanoparticles. The adsorption on the surface was due to a cooperative attraction of both charges. Recently, the process has been modified allowing the surfaces to be densely coated using oppositely charged nanoparticles using an alternating electric field. However, this approach requires specially designed equipment.

Previously unpublished Polish patent application P-391217 "Metoda pokrywania powierzchni nanocząstkami"("Process for surface coating with nanoparticles") relates to the coating of hydrophilic surfaces with a monolayer of positively charged nanoparticles. The coating was performed by immersing the substrates in a solution of the positively charged organic layer-coated nanoparticles and salt. The adsorption on the surface was carried out by a salting-out effect.

US 2010/0009379 A1 discloses methods and compositions for the selective separation and measurement of analytes using superficially heterogeneously modified surfaces to which nanoparticles are bound. The nanoparticles comprise a core and a shell, the shell being formed from cationic and anionic ligands.

US 2009/0110642 A1 discloses methods for making surface-modified nanoparticles that are suitable for bio-imaging methods. The core of these nanoparticles consists of different metals, their shell consists of organic ligands that are bound to the nucleus via metal-thiolate bonds.

Belegrinou et al. (S. Belegrinou, J. Dorn, M. Kreiter, K. Kita-Tokarczyk, E.- K. Sinner, W. Meier, Biomimetic supported membranes from aphiphilic block copolymer, Soft Matter, 2009, 6, pp. 179-1869 ) discloses methods for preparing biomimetic polymer bilayers on a solid support wherein the polymer bilayer is made by a combination of the Langmuir-Blodgett technique and the Langmuir-Schaefer transfer technique.

A disadvantage of all methods based on electrostatic attraction are the problems with the production of a dense nanoparticle monolayer due to the repulsion of nanoparticles charged with the same name. The methods described above are limited to only one type of nanoparticles. In addition, due to the electrostatic attraction of oppositely charged nanoparticles or nanoparticles having a charged surface, often the monolayer produced has no charge.

The object of the present invention is to provide a method for producing a monolayer of nanoparticles of the same name loaded with amphiphilic character.

worin Y R₁R₂R₃A⁺B^– bedeutet, A N oder P bedeutet, B ein anorganisches oder organisches Anion bedeutet,
worin R₁, R₂, R₃ H, Alkyl, Alkenyl, Alkinyl, Cycloalkyl, Cycloalkenyl, Cycloalkinyl, Aryl, Heteroaryl bedeuten, wobei R₁, R₂, R₃ miteinander verbunden werden können,
X S oder Se bedeutet, n von 1 bis 20 beträgt, m von 0 bis 2 beträgt, p von 0 bis 2 beträgt, beschichtet sind,
wobei das Verfahren dadurch gekennzeichnet ist, dass die Monoschicht aus Nanopartikeln durch vertikales, im Verhältnis zur Monoschicht, Eintauchen oder Austauchen eines Substrates auf dessen Oberfläche aufgebracht wird, und wobei zuvor eine Monoschicht von Nanopartikeln in Methanol/Dichlormethan auf die Oberfläche des Wassers aufgebracht und mittels Langmuir-Blodgett-Technik auf dieser Oberfläche dicht zusammengepresst wurde.A first subject of the present invention is therefore a process for the preparation of a monolayer of nanoparticles comprising hydrophilic, positively charged ligands selected from the group comprising the compounds of the formula 1a, 1b or 1c:

wherein YR ₁ R ₂ R ₃ A ⁺ B ^- is AN or P, B is an inorganic or organic anion,
in which R ₁ , R ₂ , R _{3 are} H, alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, cycloalkynyl, aryl, heteroaryl, where R ₁ , R ₂ , R ₃ can be linked together,
X is S or Se, n is from 1 to 20, m is from 0 to 2, p is from 0 to 2, coated,
the method being characterized in that the monolayer of nanoparticles is applied to the surface thereof by vertical, relative to the monolayer, immersion or emanation of a substrate, and wherein previously a monolayer of nanoparticles in methanol / dichloromethane is applied to the surface of the water and by means of Langmuir-Blodgett technique was tightly compressed on this surface.

worin Y COO^–, SO₃ ^–, SO₄ ^–, HPO₃ ^–, PO₃ ^2– oder Phenoxy-Anion bedeutet,
X S oder Se bedeutet, n von 1 bis 20 beträgt, m von 0 bis 2 beträgt, p von 0 bis 2 beträgt.According to the invention, the method is characterized in that the hydrophilic ligands are selected from the group comprising the compounds of the formula 1a, 1b or 1c:

wherein Y is COO ^-, SO ₃ ^-, SO ₄ ^-, HPO ₃ ^-, PO ₃ ^2- or represents phenoxy anion,
X is S or Se, n is from 1 to 20, m is from 0 to 2, p is from 0 to 2.

worin R Alkyl, Alkenyl, Alkinyl, Cycloalkyl, Cycloalkenyl, Cycloalkinyl, Aryl, Heteroaryl bedeutet,
X S oder Se bedeutet, n von 1 bis 20 beträgt, m von 0 bis 2 beträgt, p von 0 bis 2 beträgt.The nanoparticles according to the invention are preferably additionally coated with hydrophobic ligands, these being selected from the group comprising the compounds of the formula 2a, 2b or 2c:

wherein R is alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, cycloalkynyl, aryl, heteroaryl,
X is S or Se, n is from 1 to 20, m is from 0 to 2, p is from 0 to 2.

Most preferably, the hydrophilic ligand is 11-mercaptoundecyltrimethylammonium chloride, TMA, or a tetramethylammonium salt of 11-mercaptoundecanoic acid, and the hydrophobic ligand is 1-undecanethiol.

Preferably, the hydrophilic ligands are from 1 to 100%, more preferably from 1 to 20%, and most preferably from 10 to 15% of all ligands on the nanoparticle surface.

The nanoparticles can only be coated with hydrophilic ligand.

In one of the preferred embodiments, the nanoparticles are metal nanoparticles, preferably selected from the group comprising Au, Ag, Pt, Pd, Ir, Ru, Ni, Cu, Zn and their alloys.

In another preferred embodiment, the nanoparticles are semiconductor nanoparticles, preferably selected from the group consisting of Ge, CdS, CdSe, CdTe, InP, InAs, InSb, PbS, InAs, ZnO, ZnSe, ZnS, ZnTe, HgTe, GaS, GaP, GaSb, GaN, AlN, AlP, AlAs, AlSb, AgS, YBa ₂ Cu ₃ O ₇ and mixtures thereof.

In yet another preferred embodiment, the nanoparticles are bicomponent or multicomponent nanoparticles having a core-shell construction, with an upper layer preferably comprising CdSe, ZnS, ZnSe.

The nanoparticles are preferably CdTe / CdSe, CdSe / ZnS or CdSe / ZnSe nanoparticles.

Preferably, the size of the nanoparticles is from 1 nm to 100 nm.

The invention also encompasses a layer of nanoparticles according to the invention, and preferably a monolayer of these nanoparticles and a surface coated with this layer, characterized in that the layer has been produced in a method according to any one of the preceding claims.

The following are preferred variants of an exemplary process for preparing the above-mentioned nanoparticles.

According to the invention, the charged nanoparticles are produced by coating them with hydrophilic ligands and possibly with hydrophobic ligands.

In the synthesis, a mixture of ligands with hydrophobic or hydrophilic end groups in the appropriate ratio is used.

The content of the hydrophilic group ligand on the nanoparticle surface after the reaction corresponds to the content of this ligand in the reaction mixture.

Synthesized nanoparticles are purified by dissolution in a MeOH / iPrOH mixture and then by precipitation with hexane.

For dissolution EtOH or iPrOH is used.

For precipitation pentane, heptane, acetate, cyclohexane or hexane fraction are used.

The dissolution-precipitation method is repeated 3-10 times.

Alternatively, contaminants are removed using chloroform or methylene chloride in an ultrasonic cleaner.

Below, preferred variants of an exemplary method for producing a layer of the above-mentioned nanoparticles are presented.

A monolayer consisting of nanoparticles with a certain surface charge of the same name is produced at the phase boundary between water and air.

The nanoparticles containing the polar ligand in the range 0-100% form layers at the phase boundary water-air with positive or negative charge.

The nanoparticles dissolved in MeOH / DCM are applied to the water surface with a syringe.

The methanol content in the solvent mixture is 0-80% vol. in relation to methylene chloride.

The concentration of nanoparticles used for application is 0.1-30 μM.

A dense monolayer is made by compressing the monolayer using Langmuir-Blodgett technique.

The speed of compression is 2-100 cm ² / min.

The transfer of the produced layer is carried out by vertical, in relation to the monolayer, immersion or dewatering of substrates.

Preferably, for better transfer of the layer to the surface, the substrates are immersed in the aqueous subphase prior to application of the nanoparticle solution and then emerged at maximum compressed monolayer at an angle 0-45 °.

Preferably, the surface to be coated is a surface selected from glass, ITO, silicon, gallium arsenide or other semiconductors.

The invention will be explained in more detail below with reference to the preferred embodiments with reference to accompanying drawings. Show it:

1 , Measured isotherms for positively charged gold nanoparticles.

2 , Measured isotherms for negatively charged silver nanoparticles.

3 , Recording of a glass plate after transfer of the monolayers of positively charged gold nanoparticles (a) and negatively charged silver nanoparticles (b).

4 , SEM image of a monolayer of positively charged gold nanoparticles on a silicon surface.

5 , SEM image of a monolayer of negatively charged silver nanoparticles on a silicon surface.

6 , SEM image of a monolayer of positively charged gold nanoparticles with high polydispersity on a silicon surface.

7 , Image of the hydrophilic surface of a glass plate coated on both sides with positively charged gold nanoparticles and the contact angle measured according to Example 7.

8th , Image of the hydrophobic surface of a glass plate coated on both sides with positively charged gold nanoparticles and the contact angle measured according to Example 8.

Material and equipment

Reagents were purchased from Sigma-Aldrich, reagent grade solvents from Chempur. Millipore water 15 MΩ was used in all experiments. The glass plates were purchased from Roth, silicon waffle from Cemat Silicon SA. The surfaces were cut manually to the planned dimensions on site. The measurements of isotherms and the application were carried out on a Langmuir scale (50 mm × 750 mm × 10) from Nima. The measurements of the surface potential were carried out with a Zetasizer from Malvern. The images of the nanoparticle-coated silicon surfaces were taken with a Zeiss Scanning Electron Microscope (SEM) at the Institute of Physics of the Polish Academy of Sciences.

Experimental part

Silicon and glass were washed with a piranha solution (a mixture of concentrated sulfuric acid and 30% hydrogen peroxide in a volume ratio of 3: 1) and then rinsed with distilled water and methanol.

Gold and Siber nanoparticles having a metal core diameter of about 5-8 nm were prepared according to a literature method [Jana N.R., Peng G.X., J. Am. Chem. Soc., 2003, 125, 14280-14281]. The nanoparticles produced are coated with amino ligands and stabilized with a surfactant.

To prepare positively charged gold and Siber nanoparticles, 11-mercaptoundecyltrimethylammonium chloride (TMA) (hydrophilic ligand) and commercial 1-undecanethiol (hydrophobic ligand) were used.

TMA was synthesized in three steps from 11-bromo-1-undecene.

• a) der Niederschlag der Nanopartikel wurde in Methanol (2 ml) gelöst, anschließend wurde 2 ml Isopropanol zugegeben und mit n-Hexan (40–50 ml) ausgefällt. Der ausgefällte Niederschlag wurde zentrifugiert (4000–6000 rpm) und der Auflösung-Fällung-Zyklus wurde 5–7 mal wiederholt;
• b) der Niederschlag der Nanopartikel wurde mit Methylenchlorid (30 ml) mit einem Ultraschallreiniger gewaschen, und anschließend zentrifugiert (4000–6000 rpm). Der Zyklus wurde 5–7 mal wiederholt.

General description of the method for producing positively charged nanoparticles: To the solution of the nanoparticles (0.04 mmol converted to gold) methanol (20 ml) was added. After precipitation of the nanoparticles, the solution was decanted. The prepared nanoparticles were dissolved in 5 ml of chloroform. The solution of nanoparticles was injected into a mixed thiol ligand solution (0.04 mmol) with a predetermined ratio in chloroform (5 ml). After 5 minutes, the mixture was stopped and the solution left for the night. The nanoparticles were then centrifuged off and purified by dissolution precipitation (a) or washing with methylene chloride (b):

• a) The precipitate of the nanoparticles was dissolved in methanol (2 ml), then 2 ml of isopropanol were added and precipitated with n-hexane (40-50 ml). The precipitate precipitated was centrifuged (4000-6000 rpm) and the dissolution-precipitation cycle was repeated 5-7 times;
• b) The precipitate of the nanoparticles was washed with methylene chloride (30 ml) with an ultrasonic cleaner, and then centrifuged (4000-6000 rpm). The cycle was repeated 5-7 times.

Purified nanoparticles were dissolved in methanol to produce 0.02 M (converted to gold) solutions.

Commercially available 1-undecanethiol (hydrophobic ligand) and 11-mercaptoundecanoic acid (hydrophilic ligand) were used to prepare negatively charged gold and silver nanoparticles.

General description of the method for producing negatively charged nanoparticles: the nanoparticles were synthesized and purified according to the method for positively charged nanoparticles. The purified precipitate of the nanoparticles functionalized with acid ligands (0.04 mmol to gold) was dissolved in 2 ml of methanol to which 25% methanol solution of tetramethylammonium hydroxide (0.30 mmol) was added followed by n-hexane ( 50 ml) precipitated. To remove the base excess, the nanoparticles were washed with methylene chloride with the aid of ultrasound by the abovementioned method.

The absence of free ligands and other impurities in the synthesized nanoparticles was detected by ¹ H NMR spectra in CD ₃ OD. To determine the ligand ratio at the nanoparticle surface, the synthesized nanoparticles were observed with a small amount of iodine in CDCl ₃ , and then the ¹ H NMR spectra were recorded.

Brief description of the Langmuir-Blodgett technique and the ξ-potential: Definitions and methods for the calculation of important parameters

Langmuir's Libra is a shallow trough filled to the brim with pure water (carrier phase). On the surface of the water are two sheets of Teflon or other plastic used to compress the membranes formed by the molecules adsorbed on the surface.

A drop of a surfactant solution in a volatile solvent is applied to the water surface between both plates with a suitable pipette or microsyringe and, after evaporation of the solvent, a monomolecular layer is formed.

The monolayers can be applied to the surface of solids. For this purpose, a solid plate is immersed in a liquid, on the surface of which is a monolayer of amphiphilic particles. By pushing the surface limiting beams on the surface, a tightly packed layer is formed. The highly surface-interacting molecules of the monolayer are transferred to the surface of the solid during dipping or dipping.

The most important guideline for the properties of the amphiphilic materials is the π-A compression isotherm, which can be determined by measuring the surface tension of a subphase-covering monolayer, as a function of the surface area of the material accessible to a material.

The trough is equipped with a platinum-Wilhelmy plate, which allows to record changes in the surface tension, as well as connected to an electronic balance and coupled to a computer.

The zeta potential (ξ potential) is the electrical potential that exists at the phase boundary (adsorption and diffusion phase) of a particle that is at a small distance from the surface. If the zeta potential is known, the effective (net) charge on the surface of a nanoparticle can be calculated: Q _ef = 4πε _r ∈ ₀ ξR where: Q - electrical charge, ε _r - relative electrical permittivity of a medium, ε ₀ - electrical permittivity of the vacuum, ξ - zeta potential, R - radius of the nanoparticle.

The theoretical charge on the nanoparticle surface: Q = ne where: n - number of charged ligands, e - elemental electric charge.

Preferred embodiments

Example 1 - Isotherm of a monolayer of gold nanoparticles with positive charge

The experiment used gold nanoparticles with a TMA ligand content of about 13%. The nanoparticles were loaded on a Langmuir scale (344 cm ² ) in the amount of about 0.8 μmol (converted to gold) in a solution of CH ₂ Cl ₂ -CH ₃ OH (5: 1 v / v) with a Syringe applied. After the nanoparticles were applied, one waited 5 minutes, and then the monolayer was compressed at a rate of 10 cm ² / min. 1 ). A rapid increase in surface tension indicates that the liquid phase was absent in the monolayer formed. A bend of the curve in the high pressure region indicates the formation of the second layer or the aggregates.

Example 2 Isotherm of a Monolayer of Negative Charge Silver Nanoparticles

In the experiment, silver nanoparticles with a MUA ligand content of about 13% were used (the ligand had been previously deprotonated). The nanoparticles were loaded on a Langmuir scale (344 cm ² ) in the amount of about 1.4 μmol (converted to silver) in a solution of CH ₂ Cl ₂ -CH ₃ OH (1: 1 v / v) with a Syringe applied. After the nanoparticles were applied, they waited 5 minutes and then the monolayer was compressed at a rate of 10 cm ² / min. 2 ). A rapid increase in surface tension indicates that the liquid phase was absent in the monolayer formed. When the bending point was exceeded, agglomeration of the nanoparticles was observed, beginning at edges of the moving plates.

Example 3 - Coating of glass

With the method according to the invention, a glass surface with a monolayer of nanoparticles was coated by vertical removal from the solution at a constant, automatically adjustable surface tension. Before the experiment had begun, the plates were placed in aqueous phase with a holder perpendicular to the water surface. The monolayer of nanoparticles was transferred with an automatic dipper moving upwards at a rate of 10 mm / min, with a surface tension of: a) 40 mN / m, positively charged gold nanoparticles with a TMA ligand content of ca. 13% ( 3a ); b) 40 mN / m, negatively charged silver nanoparticles with a deprotonated MUA ligand content of about 15% ( 3b ).

Example 4 - Coating of Silicon with Positively Charged Monolayer of Gold Nanoparticles

With the method according to the invention a silicon surface according to Example 3 was coated. The monolayer of nanoparticles was transferred with an automatic dipper at a speed of 10 mm / min at a surface tension of 40 mN / m. 4 presents a photograph of the surface produced with a scanning electron microscope.

Example 5 Coating of Silicon with Negatively Charged Monolayer of Silver Nanoparticles

With the method according to the invention, a compressed monolayer of silver nanoparticles having a surface tension of 40 mN / m was applied by dipping a previously immersed silicon plate at an angle of approximately 45 °. 5 presents a photograph of the surface produced with a scanning electron microscope.

Example 6 - Coating of Silicon with Positively Charged Monolayer of Gold Nanoparticles with High Polydispersity

The nanoparticles were prepared according to a literature method [Shen C., Hui C., Yang T., Xiao C., Tian J., Bao L., Chen S., Ding H., Gao H., Chem. Mater., 2008, 20, 6939-6944].

With the method according to the invention a silicon surface according to Example 3 was coated. The monolayer of nanoparticles with a TMA ligand content of about 13% was transferred vertically with an automatic dipper at a speed of 10 mm / min at a surface tension of 40 mN / m. 6 presents a photograph of the surface produced with a scanning electron microscope. The example shows that silicon can be coated with a monolayer of nanoparticles having a high polydispersity by the method according to the invention.

Example 7 - Transfer of a positive charge monolayer onto a highly hydrophilic glass surface

Using the method according to the invention, glasses with a hydrophilic surface were coated with a monolayer of gold nanoparticles having a TMA ligand content of about 13% by vertical removal from the solution at a constant, automatically adjustable surface tension. First, the glass plate was held in a potassium hydroxide-isopropanol solution, then washed with distilled water and methanol. A prepared glass plate was placed in the aqueous phase with a holder. The monolayer of nanoparticles was transferred with an automatic dipper moving upwards at a speed of 10 mm / min at a surface tension of 40 mN / m. After application of the nanoparticles, the plate surface showed a significant decrease in hydrophilicity - the contact angle increased from 17 to 83 degrees ( 7 ).

Example 8 - Transfer of a positive charge monolayer to a highly hydrophobic glass surface

With the process according to the invention, glasses having a hydrophobic surface were coated with a monolayer of gold nanoparticles having a TMA ligand content of about 13% by vertical immersion in the aqueous phase at a constant, automatically adjustable surface tension. The hydrophobic glass surface was prepared in the reaction with the 1-dodecyltrichlorosilane. A prepared glass plate was placed in the aqueous phase with a holder. The monolayer of nanoparticles was transferred with an automatic dipper moving down at a rate of 10 mm / min at a surface tension of 40 mN / m. After application of the nanoparticles, the plate surface showed a decrease in hydrophobicity - the contact angle decreased from 100 to 61 degrees ( 7 ). After transfer, the surface became more hydrophilic ( 7 ).

Example 9 - Charges After Monolayer Preparation

The silver nanoparticles containing negatively charged ligand (deprotonated 11-mercaptoundecanoic acid) of about 15% in methanol show a zeta potential of -17.4 mV. A monolayer formed from the silver nanoparticles was transferred to a Teflon substrate and then rinsed in methanol by transferring the nanoparticles from the film to the solution. The prepared solution had a zeta potential of -17.2 mV.

The gold nanoparticles with a content of positively charged ligand (TMA) of about 13% in methanol show a zeta potential of +34.6 mV. A monolayer formed from the gold nanoparticles was transferred to a Teflon substrate and then rinsed in methanol by transferring the nanoparticles from the film to the solution. The prepared solution had a zeta potential of +34.4 mV.

The results obtained indicate the charge retention after the formation of the monolayer and its transfer to a solid substrate.

Example 10 - Calculation of the electric charge of a monolayer

The effective charge on the surface of a silver nanoparticle with a diameter of 5 nm is approximately -2.4 × 10 ^-19 C, which corresponds to 1.5 elementary charges. The theoretical charge calculated from the number of ligands is -88 × 10 ^-19 C (55 element charges). The effective charge of a monolayer is about -3.6 × 10 ^-3 C / m ² .

The effective charge on the surface of a 8 nm diameter Au nanoparticle is approximately 6.8 × 10 ^-19 C, which corresponds to 4.3 elemental charges. The theoretical charge calculated from the number of ligands is 196 × 10 ^-19 C (122 element charges). The effective charge of a monolayer is about +5.0 × 10 ^-3 C / m ² .

A low - calculated on the basis of zeta potential - effective, measured in methanol / water mixture charge in relation to the total number of charged ligands is caused by the following factors: (i) low degree of dissociation of nanoparticle ligands in methanol; and (ii) the presence of a star layer which screens off the dissociated charges on the nanoparticle surface.

The project is part of the European Regional Development Fund (ERDF) under:
Co-financed by the Innovative Economy Operational Program OP IE 2007-2013 OPIG.01.01.02-00-008 / 08.
Project title: Quantum Semiconductor Nanostructures for Applications in Biology and Medicine - Development and Commercialization of New Generation of Devices for Molecular Diagnostics Based on New Polish Semiconductor Devices.

Claims (15)

Process for the preparation of a monolayer of nanoparticles containing hydrophilic, positively or negatively charged ligands selected from the group comprising the compounds of the formula 1a, 1b or 1c:

wherein Y is COO ^- , SO ₃ ^- , SO ₄ ^- , HPO ₃ ^- , PO ₃ ^2- or phenoxy anion or Y in the form R ₁ R ₂ R ₃ A ⁺ B ^- , wherein AN or P, B an inorganic or organic anion, R ₁ , R ₂ , R _{3 is} alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, cycloalkynyl, aryl, heteroaryl, where R ₁ , R ₂ , R ₃ can be joined together, X is X or Se means , n is from 1 to 20, m is from 0 to 2, p is from 0 to 2, coated, the method characterized in that the monolayer of nanoparticles by vertical, in relation to the monolayer, immersion or erosion of a substrate on the surface of which is applied, and wherein previously a monolayer of nanoparticles in methanol / dichloromethane was applied to the surface of the water and pressed tightly by means of Langmuir-Blodgett technique on this surface. The method of claim 1, characterized in that the nanoparticles are additionally coated with hydrophobic ligands, wherein these are selected from the group comprising the compounds of formula 2a, 2b or 2c:

wherein R is alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, cycloalkynyl, aryl, heteroaryl, X is S or Se, n is from 1 to 20, m is from 0 to 2, p is from 0 to 2. The method of claim 1 or 2, characterized in that the hydrophilic ligand is 11-mercaptoundecyltrimethylammonium chloride, TMA, or a tetramethylammonium salt of 11-mercaptoundecanoic acid, and the hydrophobic ligand is 1-undecanethiol. The method according to any of the preceding claims, characterized in that the hydrophilic ligands represent from 1 to 100% of all ligands on the nanoparticle surface. The method of any one of the preceding claims, characterized in that the hydrophilic ligands represent from 1 to 20% of all ligands on the nanoparticle surface. The method according to any of the preceding claims, characterized in that the hydrophilic ligands represent from 10 to 15% of all ligands on the nanoparticle surface. The method according to any one of the preceding claims, characterized in that the nanoparticles are metal nanoparticles. The method according to any one of the preceding claims, characterized in that the metal nanoparticles are selected from the group comprising Au, Ag, Pt, Pd, Ir, Ru, Ni, Cu, Zn and their alloys. The method according to claims 1, 2, 3, 4, 5 or 6, characterized in that the nanoparticles are semiconductor nanoparticles. The method according to claim 9, characterized in that the semiconductor nanoparticles are selected from the group comprising Ge, CdS, CdSe, CdTe, InP, InAs, InSb, PbS, InAs, ZnO, ZnSe, ZnS, ZnTe, HgTe, GaS, GaP, GaSb, GaN, AlN, AlP, AlAs, AlSb, AgS, YBa ₂ Cu ₃ O ₇ and mixtures thereof. The method according to claims 1, 2, 3, 4, 5 or 6, characterized in that the nanoparticles are two- or multi-component nanoparticles having a core-shell structure. The method of claim 11, characterized in that the two- or multi-component nanoparticles having a core-shell structure have an upper layer comprising CdSe, ZnS, ZnSe. The method according to claims 11 and 12 characterized in that the nanoparticles are CdTe / CdSe, CdSe / ZnS or CdSe / ZnSe nanoparticles. The method according to any one of the preceding claims, characterized in that the size of the nanoparticles is from 1 nm to 100 nm. Surface coated with a layer of nanoparticles, characterized in that the layer has been produced in a process according to any one of the preceding claims.

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