WO2009077599A2

WO2009077599A2 - Nanospheres with external surface of noble metal

Info

Publication number: WO2009077599A2
Application number: PCT/EP2008/067926
Authority: WO
Inventors: Giovanni Baldi; Marco Bitossi; Daniele Bonacchi
Original assignee: Colorobbia Italia S.P.A.
Priority date: 2007-12-19
Filing date: 2008-12-18
Publication date: 2009-06-25
Also published as: ITFI20070285A1; WO2009077599A3

Abstract

There are described nanosphere particles having a core of biocompatible organic or inorganic material and a noble material coating capable of absorbing electromagnetic radiations in the visible and infrared spectrum.

Description

Nanospheres with external surface of noble metal

Field of the invention

The present invention relates to products capable of absorbing electromagnetic radiations in the visible and infrared spectrum. Background art

Noble metals in the nanoparticle form, and specifically gold, have always attracted both the academic and the industrial world for their particular optical properties which anticipate, for example, their use in the biomedical field both for the preparation of specific contrast-agents or markers, when coupled to selective molecules, and for photothermal therapy of certain types of tumors.

It has recently been discovered that gold nanoparticles may be used as transformers of electromagnetic energy into localized thermal energy for the treatment of some types of cancer (photothermal cancer therapy) [El-Sayed I. H. et Al. Cancer Letter (2006), 239, 129]. However, a limitation to their use resides in that the gold nanoparticles known heretofore have a maximum absorption of about 520nm and in that the electromagnetic radiation having this wavelength has a poor penetrability. These limits may be overcome by using gold particles having specific geometries (hollow spherical, cylindrical, dendritic) which are capable of absorbing in near infrared zone [El Sayed et Al Nanotoday, (2007) 18-29].

Unfortunately, although gold nanoparticle chemistry has been being studied for some time [Astruc M. C. D. and D. Chem. Rev. (2004), 104, 293-346], the synthesis thereof to sizes below 500nm with high absorptions in the near infrared region still has various problems which limited the development thereof; indeed, the production techniques of these nanoparticles are still currently very complex, have a low efficiency, are difficult to be scaled for producing large amounts (more than 500ml) and, above all, the final result is difficult to be repeated. Furthermore, the main production technique of gold nanoparticles absorbing in the infrared uses a silica core, the toxicity of which is currently debated (Weisheng Una, Yue-wern Huangb, Xiao-Dong Zhouc and Yinfa Maa Toxicology and Applied Pharmacology, Volume 217, Issue 3, 15 December 2006, Pages 252-259). It is therefore apparent the importance of being able to obtain nanometric particles having a noble material surface capable of absorbing the radiations in the visible and infrared spectrum and an effective preparation process of said particles, which do not include the use of potentially toxic substances.

Summary of the invention The present invention allows to overcome the aforesaid problems in virtue of nanoparticles consisting of a core of biocompatible material (organic or inorganic) coated by a noble metal, which have been proven capable of absorbing the electromagnetic radiation both in the visible and infrared spectrum.

Brief description of the drawings Figure 1 shows the visible absorption spectrum of the noble metal nanoparticle dispersion of the invention as obtained from Example 1.

Figure 2 shows the visible absorption spectrum of the noble metal nanoparticle dispersion of the invention as obtained from Example 2.

Figure 3 shows the size distribution obtained by dynamic light scattering in the dispersion obtained with the procedure of the invention according to Example 2.

Figure 4 shows the potential change Z, measured before and after the stabilization with albumine of the solution obtained in Example 2.

Detailed description of the invention

The present invention allows to overcome the aforesaid problems in virtue of nanoparticles consisting of a core of biocompatible material (organic or inorganic) coated by a noble metal, which have been proven capable of absorbing the electromagnetic radiation both in the visible and infrared spectrum.

According to the invention, noble metals are: gold, silver and copper.

The biocompatible materials which form the core of the particle consist of iron oxide nanoparticles: Fe2O3, Fe3O4 or mixed iron oxides, such as for example:

CoFe204, ZnFe2O4, MnFe2O4 possibly functionalized by bifunctional binders, or by particles of a biocompatible material weakly soluble in water.

Examples of functionalized cores according to the present invention are described in parallel patent application PCT/EP2007/050036 (to the same applicant). The bifunctional binders as mentioned above are chosen from: thiols, carboxylic acids, hydroxamic acids, phosphoric acids, esters and aliphatic chain salts thereof, having an aliphatic chain which carries a second functional group at the terminal position (named position ω).

More specifically, the formula of said bifunctional binders is:

where: n is an integer from 2 to 20;

R₁ is chosen from: CONHOH, CONHOR, PO(OH)₂, PO(OH)(OR), COOH, COOR,

SH, SR; R₂ is chosen from: OH, NH₂, COOH, COOR;

R is an alkyl group or an alkali metal.

The preferred alkali metals are K, Na, or Li, while the preferred alkyl groups are C_1-

₆alkyl, more specifically ethyl.

The core functionalization with said bifunctional binders is obtained according to known procedures, or as described in the aforesaid patent application

PCT/EP2007/050036, e.g. by reacting the bifunctional derivative dissolved in ethanol with the core so as to coat the surface thereof.

In practice, a dispersion of nanoparticles in organic solvent (e.g. ethylene glycol) is reacted with the desired binding agent by mixing at low temperature for a few hours and possibly by separating the products by extraction with particular solvents or by precipitation e.g. with acetone.

The particles of biocompatible material weakly soluble in water, for example, consist of polyesters, cholesterol, thiols and the like, and are prepared according to known methods by dissolving the biocompatible material in partially or totally water-soluble solvents (such as ethanol, higher alcohol, acetone) and by injecting said mixture in water in the presence of surfactants or not, including anionic surfactants (more specifically dodecyl sodium sulfate) and thiols, so as to generate nanoparticles of organic material in the range of 5-200 nm, more typically 80 nm.

It has further been surprisingly found, and is a further object of the present invention, a process for growing the noble metals on the core of biocompatible organic or inorganic material, as defined above.

Specifically, according to said process, to a core solution is added a neutral-pH noble material solution along with an organic reducer is added so as to reduce the metal ions into metal which deposits on the surface of the nanoparticles (normally in a few weeks).

Such a process may be modified by adding to the core solution, before adding the noble metal solution, a pre-formed solution of noble metal nanoparticles obtained by reduction of tetrachloroauric acid with sodium borohydride or sodium citrate, according to known methods.

The reduction process may be sped up by the exposure to ultraviolet rays.

The growing process may be iteratively repeated by adding more neutral pH ionic metal and organic reducer, thus increasing the noble metal thickness on the surface of the core; noble metal coating thicknesses in the range, for example, of

1 -40 nm may thus be obtained.

If required, in order to stabilize the solution, synthetic and natural polymers

(including proteins) which contain amino groups, thiols, disulphides and thioethers, particularly albumine, may be added thereto.

Some examples for better understanding the invention are provided below.

Example 1

Synthesis of ferrite cobalt nanoparticles having a gold coating

0.3g of an aqueous dispersion of ferrite cobalt nanoparticles functionalized with 1.5% w/w para-amino benzoic acid are added to 20Og of 0.02% solution of gold nanoparticles obtained by means of the reduction method with tetrachloroauric acid citrate.

After a 24 hour wait, 50ml of a 0.15% w/w solution of tetrachloroauric acid taken to pH 6 by means of the addition of soda is added. 0.92g of a 3.7% w/w formaldehyde solution are added to the final solution, and all left to rest for a week.

At the end of this time, a dark solution capable of absorbing in the near infrared is formed.

The visible absorption spectrum of the obtained dispersion is shown in Fig. 1.

Example 2 Synthesis of cholesterol nanoparticles having a gold coating

A dispersion of cholesterol nanoparticles is prepared by injecting 2.5ml of a 0.36% cholesterol solution in isopropanol into 5Og of an aqueous solution containing 1 % of dodecyl sodium sulfate and 0.5% of dodecanthiol. The solution is placed under rotating pump vacuum so as to eliminate the isopropanol in excess.

50 ml of this solution are added to 50ml of a 0.15% tetrachloroauric acid solution neutralized to pH6 by adding soda. After a 2 hour wait, 0.92g of a 3.7% aqueous solution of formaldehyde are added. After one week, a dark coloring of the solution, capable of absorbing in all the visible and infrared spectrum as shown by the spectrum in Figure 2, is observed.

Finally, Figure 3 shows the size distribution obtained by dynamic light scattering in the dispersion obtained with the procedure of Example 2. Example 3

Stabilization of the products in Examples 1 and 2

5Og of solution obtained as in Examples 1 or 2 are added to an aqueous solution containing 0.45 g of albumine.

The final product binds with the albumine as shown in Figure 4, which illustrates the potential change Z, measured before and after the stabilization of the solution obtained in Example 2, respectively.

Claims

1. Nanoparticles consisting of a core of organic or inorganic biocompatible material coated with a noble metal.

2. Nanoparticles according to claim 1 , wherein said noble metals are: gold, silver and copper.

3. Nanoparticles according to claims 1 and 2, wherein said biocompatible materials which form the particle core consists of iron oxide III and IV or mixed iron oxide nanoparticles, possibly functionalized with bifunctional binders, or of particles of a biocompatible material weakly soluble in water.

4. Nanoparticles according to claim 3, wherein said iron oxides are chosen from: Fe2O3, Fe3O4 and said mixed iron oxides are chosen from: CoFe204, ZnFe2O4, MnFe2O4.

5. Nanoparticles according to claim 3, wherein said bifunctional binders are chosen from: thiols, carboxylic acids, hydroxamic acids, phosphoric acids, esters and aliphatic chain salts thereof, having an organic spacer which carriers a second functional group at the terminal position (named position ω).

6. Nanoparticles according to claim 3, wherein the particles of biocompatible material weakly soluble in water consists of: polyesters, cholesterol, thiols and the like.

7. A method for preparing nanoparticles according to claims 1 -6, wherein:

- to a core solution is added a neutral-pH noble material solution along with an organic reducer so as to reduce the metal ions into metal which deposits on the surface of the nanoparticles;

- possibly, the addition of noble metal solution and organic reducer is repeated once or more times;

- the final solution is stabilized with synthetic or natural polymers.

8. A method according to claim 7, wherein a noble metal nanoparticle solution is previously added to the core solution.

9. A method according to claim 7, wherein said organic reducing agent is formaldehyde.

10. A method according to claim 7, wherein said synthetic and natural polymers are polymers containing amino groups, thiols, disulphides and thioethers.

1 1.A method according to claim 9, wherein said natural polymers are proteins.

12. A method according to claim 10, wherein said protein is albumine.

13. Use of nanoparticles according to claims 1 -6 as specific contrast-agents or markers.

14. Use of nanoparticles according to claims 1 -6 for the preparation of agents used in photothermal cancer therapy.