Synthesis of core-shell nanoparticles and applications of said nanoparticles for surface enhanced Raman scattering
A method of synthesizing of gold-silver core-shell nanoparticles, from a colloidal aqueous solution of gold seeds with surfactant, the gold-silver core-shell nanoparticles being produced from anisotropic gold seeds, said method comprising adding to the colloidal aqueous solution a precursor of silver and a reducing agent, to produce the deposition of silver on the gold seeds in a step called principal, characterized in that the method has an incubation step of the colloidal aqueous solution containing the gold seeds with surfactant in the DMSO, prior to the principal step.
1. A method of synthesizing gold-silver core-shell nanoparticles from a colloidal aqueous solution of gold seeds with surfactant, the gold-silver core-shell nanoparticles being produced from anisotropic gold seeds, characterized in that the method comprises successively:
an incubation step of the colloidal aqueous solution containing the gold seeds with an initial surfactant, in a mixture of water solvents and DMSO, for a first given period of time, in order to modify the organization of the initial surfactant and the assembly of the gold seeds;
a step adding an additional surfactant to the previous resultant mixture;
a heating step for the resultant mixture, for a second given period of time;
a step adding to the resultant mixture a precursor of silver and a reducing agent, to produce the deposition of silver onto the gold seeds in a step called principal during a third period of time;
an extraction step of the nanoparticles.
2. The method as claimed in claim 1 , characterized in that the ratio between the volume of DMSO and the total volume of water is less than 2 and greater than 0.1, the total volume of water being the volume contributed by the colloidal aqueous solution of gold seeds with the initial surfactant and by the water present in the mixture of solvents water+DMSO for incubation.
3. The method as claimed in claim 1 , characterized in that the ratio between the volume of DMSO and the total volume of water is less than or equal to 0.33, the total volume of water being the volume contributed by the colloidal aqueous solution of gold seeds with the initial surfactant and by the water present in the mixture of solvents water+DMSO for incubation.
4. The method as claimed in either claim 1 , characterized in that the ratio between the volume of DMSO and the total volume of water is 1, the total volume of water being the volume contributed by the colloidal aqueous solution of gold seeds with the initial surfactant and by the water present in the mixture of solvents water+DMSO for incubation.
5. The method as claimed in claim 1 , characterized in that the ratio between the volume of DMSO and the total volume of water is 1.5, the total volume of water being the volume contributed by the colloidal aqueous solution of gold seeds with the initial surfactant and by the water present in the mixture of solvents water+DMSO for incubation.
6. The method as claimed in claim 1 , characterized in that the ratio between the volume of DMSO and the total volume of water is less than 10 and greater than 2, the total volume of water being the volume contributed by the colloidal aqueous solution of gold seeds with the initial surfactant and by the water present in the mixture of solvents water+DMSO for incubation.
7. The method as claimed in claim 6 , characterized in that the ratio between the volume of DMSO and the total volume of water is Greater than or equal to 4, the total volume of water being the volume contributed by the colloidal aqueous solution of gold seeds with the initial surfactant and by the water present in the mixture of solvents water+DMSO for incubation.
8. The method of synthesizing core-shell nanoparticles according to claim 1 , characterized in that the step adding the additional surfactant takes place after a first optimal incubation time ranging from a few minutes to one hour and determined by spectroscopy, making it possible to control the assembly of the gold seeds and to obtain either one gold seed per silver shell, or two gold seeds per silver shell.
9. The method as claimed in claim 1 , characterized in that the extraction step is achieved by centrifuging.
10. The method as claimed in claim 1 , characterized in that the additional surfactant is chosen from the following list: cetyltrimethylammonium chloride (CTAC), cetyltrimethylammonium bromide (CTAB) or benzyldimethylhexadecylammonium chloride (BDAC).
11. The method as claimed in claim 1 , characterized in that, after the extraction step, the method has a new step adding a precursor of silver and a reducing agent to the nanoparticles, in order to produce an overgrowth of silver.
12. The method as claimed in claim 1 , characterized in that the reducing agent is a solution of ascorbic acid (AA) and surfactant, and in that the precursor of silver is silver nitrate.
13. Gold-silver core-shell nanoparticles produced from gold seeds of elongated shape, obtained by the method defined according to claim 1 , and having traces of DMSO visible by spectroscopy.
14. The gold-silver core-shell nanoparticles as claimed in claim 13 , characterized in that each gold-silver core-shell nanoparticle has at least two gold seeds encapsulated in the same silver shell enclosing the core.
15. The gold-silver core-shell nanoparticles as claimed in claim 14 , characterized in that for each nanoparticle, the gold seeds are disposed head-to-head in the same silver shell.
16. The gold-silver core-shell nanoparticles as claimed in claim 14 , characterized in that for each nanoparticle, the gold seeds are disposed face-to-face in the same silver shell.
17. The gold-silver core-shell nanoparticles as claimed in claim 14 , characterized in that the gold seeds are nanorods.
18. The gold-silver core-shell nanoparticles as claimed in claim 17 , characterized in that the nanorods have an average aspect ratio between 2 and 5.
19. A solid substrate for Surface Enhanced Raman Scattering (SERS) comprising gold-silver core-shell nanoparticles resulting from claim 13 , the nanoparticles being organized in one or more 2D or 3D networks on surface areas of more than 10 μm 2 , advantageously more than 40 μm 2 , for each 2D or 3D network.
20. A solid substrate for Surface Enhanced Raman Scattering (SERS) comprising gold-silver core-shell nanoparticles resulting from claim 13 , the nanoparticles being organized in one or more 1D chains, the 1D change having characteristic dimensions ranging from 2 to 3 μm.
21. The application of the substrate as claimed in claim 19 to the detection by SERS of analytes such as organic pollutants.
22. The application as claimed in claim 21 , the analyte being atrazine, the cold-silver core-shell nanoparticles being used with beta-cyclodextrin (CAS 7585-39-9) or alpha-cyclodextrin (CAS 10016-20-3).
23. The application as claimed in claim 21 , the analyte being chosen from the following list: thiram (CAS 137-26-8), phosmet (CAS 732-11-6), malathion (CAS 121-75-5), (4,4′)-BPE (CAS 13362-78-2), 4-mercaptobenzoïque acid (CAS 1074-36-8).
24. The method as claimed in claim 1 , where the initial surfactant is the same as the additional surfactant.
25. The method as claimed in claim 1 , where the initial surfactant is different from the additional surfactant.