RU2759484C1 - Method for producing gold nanorods with a given plasmon resonance position - Google Patents

Abstract

FIELD: chemistry.SUBSTANCE: invention relates to chemistry and concerns a method for producing gold nanorods, including the synthesis of a colloidal solution of gold nanorods in a mixture of cetyltrimethylammonium bromide and sodium oleate with a longitudinal plasmon resonance tuned to a wavelength from the near infrared region of the spectrum, the re-dissolution in a solution of cetyltrimethylammonium bromide and the addition of a solution of hydrochloric acid to a colloidal solution of gold nanorods.EFFECT: invention provides the possibility of obtaining nanorod colloids with controlled adjustment of plasmon resonance to a given wavelength by reducing the length of the nanorods, while maintaining the thickness and shape of the nanorods and without contamination by side chemicals.1 cl, 5 dwg, 1 tbl, 2 ex

Description

The invention relates to nanotechnology of plasmon resonance (PR) particles intended for use in various fields of science and technology, including physics, chemistry, biology, medicine and veterinary medicine.

The production of gold nanorods with a given position of plasmon resonance is an important task, since gold nanorods are one of the most commonly used gold nanoparticles in biotechnology due to several advantages, the main one being the ability to easily tune plasmon resonance. In addition, it is possible to change the ratio of absorption and scattering by changing the dimensions. There are several published synthesis protocols (Nikoobakht B., El-Sayed MA Preparation and growth mechanism of gold nanorods (NRs) using seed-mediated growth method // Chem. Mater. 2003. V.15. P. 1957-1962; Sau TK , Murphy CJ Seeded high yield synthesis of short Au nanorods in aqueous solution // Langmuir. 2004. V. 20. P. 6414-6420; Ye X., Zheng Ch., Chen J., Gao Y., Murray CB Using binary surfactant mixtures to simultaneously improve the dimensional tunability and monodispersity in the seeded growth of gold nanorods // Nano Lett . 2013. V. 13. P. 765-771) and their surface functionalization (Yu C., Irudayaraj J. Multiplex biosensor using gold nanorods // Anal. Chem. 2007. V. 79. P. 572-579; Huang X., El-Sayed IH, Qian W., El-Sayed MA Cancer cells assemble and align gold nanorods conjugated to antibodies to produce highly enhanced , sharp, and polarized surface Raman spectra: A potential cancer diagnostic marker // Nano Lett. 2007. V. 7. P. 1591-1597). The tuning range of plasmon resonance of nanorods covers the visible and near infrared region (Jain PK, Lee KS, El-Sayed IH, El-Sayed MA Calculated absorption and scattering properties of gold nanoparticles of different size, shape, and composition: applications in biological imaging and biomedicine // J. Phys. Chem. B. 2006. V. 110. P. 7238-7248) by adjusting their axial ratio. The ability to adjust plasmon resonance in the near infrared region allows the use of gold nanorods in biomedical research, since for light from this light range, the transparency of biological tissues reaches a maximum (Tuchin VV Tissue Optics: Light Scattering Methods and Instruments for Medical Diagnosis. - Bellingham: SPIE Press, 2000 - 942 p.). This advantage distinguishes nanorods from gold nanospheres, in which the plasmon resonance setting is limited to the range of 510-600 nm, depending on their size. It should be noted that the adjustment of the position of the plasmon resonance of the nanorods is directly dependent on the axial ratio (and, to a lesser extent, on the dimensions at a fixed axial ratio). Even a minimal change in their axial ratio can cause a significant change in the position of the plasmon resonance in the extinction spectrum. For some biomedical applications, it is important to fine-tune the plasmon resonance of the nanorods to a given wavelength (for example, to the laser wavelength in photothermal therapy).

A known method of adjusting the plasmon resonance of gold nanorods by selectively shortening them [Tsung C.K., Kou X., Shi Q., Zhang J., Yeung M.H., Wang J., Stucky G.D. Selective shortening of single-crystalline gold nanorods by mild oxidation // J. Am. Chem. Soc. 2006. V. 128. P. 5352-5353]. The method is based on heating a colloid of nanorods to 70-90 ° C under the action of oxygen in the presence of hydrochloric acid. It is shown that, with increasing temperature, the rate of shift of the plasmon resonance of nanorods to shorter wavelengths increases.

A known method of tuning the plasmon resonance of gold nanorods using iron chloride [Zou R., Guo X., Yang J., Li D., Peng F., Zhang L., Wang H., Yua H. Selective etching of gold nanorods by ferric chloride at room temperature // Cryst. Eng. Comm. 2009. V. 11. P. 2797-2803]. The method is based on the addition of ferric chloride to a colloid of gold nanorods at room temperature. It is shown that with an increase in the reaction time, the plasmon resonance of gold nanorods shifts towards shorter wavelengths, caused by a decrease in the size of gold nanorods.

A known method of tuning the plasmon resonance of gold nanorods using potassium cyanide [Jana NR, Gearheart L., Obare SO, Murphy CJ Anisotropic chemical reactivity of gold spheroids and nanorods // Langmuir. 2002. V. 18. P. 922-927]. The method is based on the addition of potassium cyanide to the colloid of gold nanorods. When potassium cyanide is dissolved, oxygen acts as an oxidizing agent for gold, and potassium cyanide acts as a complexing agent for gold ions. It has been demonstrated that the longitudinal plasmon resonance of gold nanorods can shift from 800 to 530 nm, which is accompanied by a decrease in the nanorod length.

The disadvantages of all of the above methods is that the setting of the plasmon resonance is kinetic in nature and is determined not by the amount of added oxidant, but by the reaction time. To stop the reaction, centrifugation and reconstitution of nanorods in water is proposed [Zou R., Guo X., Yang J., Li D., Peng F., Zhang L., Wang H., Yua H. Selective etching of gold nanorods by ferric chloride at room temperature // Cryst. Eng. Comm. 2009. V. 11. P. 2797-2803], which requires additional time, during which the plasmon resonance of the nanorods will continue to shift. Thus, the existing methods do not make it possible to obtain nanorods with a given position of the plasmon resonance. An additional disadvantage of these methods is the contamination of the colloid of gold nanorods with the chemicals used, which necessitates the subsequent purification of the colloids from the introduced substances.

A known method of oxidation of gold nanoparticles in the presence of a complex of gold with cetyltrimethylammonium bromide (CTAB) [Rodriguez-Fernandez J., Perez-Juste G., Mulvaney P., Liz-Marzan L.M. Spatially-directed oxidation of gold nanoparticles by Au (III) -CTAB complexes // J. Phys. Chem. B. 2005. V. 109. P. 14257-14261]. It was shown that the addition of chloroauric acid (HACA) to the colloid of quasi-spherical gold nanoparticles caused a change in their shape to a more rounded one and a decrease in their size. When exposed to a mixture of gold nanorods and nanocubes, it was shown that the length of the rods decreases and the cubes are transformed into spheres. The spectral kinetics of this process was also investigated.

The disadvantage of this method is that the colloidal solution of nanorods contained a large amount of side nanoparticles of a different shape - nanocubes, and the possibility of adjusting the plasmon resonance of nanorods depending on the amount of added ZHVK was not investigated. The range of concentrations of ZHVK for adjusting the position of the PR of nanorods was not determined. This method was also not used for the colloid of gold nanorods with a high content of target particles of more than 97%.

The objective of the present invention is to provide a method for the controlled tuning of the plasmon resonance of gold nanorods to a given wavelength by reducing their length while maintaining their thickness and shape by adding a certain amount of chloroauric acid.

The technical result of the present invention is the possibility of obtaining colloids of nanorods with controlled tuning of plasmon resonance at a given wavelength by reducing the length of nanorods, while maintaining the thickness and shape of nanorods and without contamination by side chemicals.

The specified technical result is achieved due to the fact that the method for obtaining gold nanorods with a given position of plasmon resonance includes the synthesis of a colloidal solution of gold nanorods in a mixture of cetyltrimethylammonium bromide and sodium oleate with a longitudinal plasmon resonance tuned to the wavelength from the near infrared spectral region, resolving to 100 mM solution of cetyltrimethylammonium bromide and adding to the colloidal solution of gold nanorods a certain amount of chloroauric acid solution in an amount from 25 to 1000 μl of 10 mM solution per 10 ml of colloid of nanorods.

The proposed method for obtaining gold nanorods with a given position of the plasmon resonance is as follows. At the first stage, a colloidal solution of monodisperse gold nanorods is synthesized in a mixture of CTAB and sodium oleate with a longitudinal plasmon resonance tuned to a wavelength from the near infrared region of the spectrum. At the second stage, the required amount of chloroauric acid is added to the colloid of gold nanorods, and controlled etching occurs along the long axis of the nanorods with a complex of Au ³⁺ ions with cetyltrimethylammonium bromide (CTAB). In this case, the axial ratio of the nanorods decreases while maintaining their thickness, and the plasmon resonance shifts towards shorter wavelengths. The final position of the plasmon resonance and the axial ratio of the nanorods are completely determined by the amount of added chloroauric acid.

The invention is illustrated by examples:

Example 1: Obtaining gold nanorods with a given position of plasmon resonance in the wavelength range of 680-925 nm.

The following reagents are used: cetyltrimethylammonium bromide (CTAB) (96%, Fluka, no. 52370), sodium oleate (> 82% fatty acid residues, Sigma-Aldrich), chloroauric acid (ZHVK) (99.99%, Alfa Aesar), silver nitrate ( AgNO ₃ ,> 99%, Alfa Aesar), ascorbic acid (> 99.9%, Sigma-Aldrich), sodium borohydride (99%, Sigma-Aldrich), 37% hydrochloric acid (high purity grade, Vekton), purified water.

Stage 1 - Synthesis of a colloidal solution of gold nanorods

For the synthesis of gold "embryos", mix 10 ml of 100 mM CTAB, 250 μl of 10 mM ZHVK and 1 ml of 100 mM sodium borohydride. The solution becomes light brown. To 250 ml of water add 7 g of CTAB and 1.234 g of sodium oleate, heat to 50 C with stirring until complete dissolution and then cool the solution to 30 C. Add 18 ml of 4 mM silver nitrate to the solution and stir the mixture for 15 minutes. Add 250 ml of 1 mM 3XVA, which causes a color change from colorless to yellow due to the formation of the Au ³⁺ -CTAB complex. Stir the solution for 90 minutes, it becomes colorless, which indicates the reduction of Au ³⁺ to Au ⁺ with sodium oleate. To reduce Au ⁺ to Au ^0, add 1.25 ml of 64 mM ascorbic acid, then add 2.1 ml of concentrated hydrochloric acid and the pH of the solution reaches 1.5. Finally, add 0.8 ml of the gold "embryos" obtained at the first stage to the growth solution. Incubate the mixture without stirring for 48 hours at 30 ° C; upon the formation of gold nanorods, the color of the mixture changes from colorless to brown. Nanorods are sedimented in a centrifuge at 10000g for 15 min and redissolved in 100 mM CTAB. For the obtained suspension of gold nanorods, the maximum of plasmon resonance in the extinction spectrum is localized at 925 nm.

Stage 2 Selective etching using ZHVK

To the suspension of gold nanorods obtained in the previous step, add the calculated amount of 10 mM ZHVK solution at the rate of 25 to 1000 μL per 10 milliliters of the suspension of nanorods (with a gold concentration of 1 mM). To adjust the plasmon resonance of the nanorods to a wavelength of 810 nm, add 147 μl of a 10 mM ZHVK solution to 10 ml of the nanorod suspension. To adjust the PR of nanorods at 740 nm, add 220.5 μL of 10 mM ZHVK solution to 10 ml of the nanorod suspension. To adjust the PR of nanorods at 680 nm, add 294 μL of 10 mM 3XVK solution. Stir the mixture on a mixer for 2 hours at 30 ° C.

Example 2: Tuning the plasmon resonance of gold nanorods in the 700-900 nm wavelength range

Stage 1 - Synthesis of a colloidal solution of gold nanorods

To synthesize gold "embryos" by adding 0.6 ml of 10 mM sodium borohydride solution to a mixture containing 0.25 ml of 10 mM ZHVA and 10 ml of 0.1 M aqueous CTAB solution, incubate the solution at room temperature for 90 min. Prepare the growth solution by following these steps. Dissolve 7 g of CTAB and 1.234 g of sodium oleate in 250 ml of water. With stirring, add 18 ml of 4 mM silver nitrate. Incubate the mixture for 15 minutes at room temperature, then add 250 ml of 1 mM ZHVK. Stir for 90 minutes and add 2.1 ml of 37% hydrochloric acid. After 15 minutes, add 1.25 ml of 64 mM ascorbic acid and 0.1 ml of the previously prepared colloidal solution of "embryos". Incubate the mixture at 30 ° C for 48 hours. Nanorods are precipitated by centrifugation at 10000g for 15 min and redissolved in 100 mM CTAB. The synthesized rods had plasmon resonance tuned to a wavelength of 900 nm.

Stage 2 Selective etching using ZHVK

To obtain nanorods with plasmon resonance at a wavelength of 886, 863, 840, 802, 788, 751, 727, and 700 nm, add 25, 50, 75, 100, 112.5, 125, 150, and 175 to 10 ml of a colloidal solution of nanorods, respectively. μl of 10 mM ZHVK solution and stir for 2 hours.

The invention is illustrated in the drawings.

The proof of the successful implementation of the proposed solution is given in Fig. 1, which shows the extinction spectra of colloids of gold nanorods up to (maximum plasmon resonance at 900 nm) and after adding different amounts of a solution of chloroauric acid at the rate of 25, 50, 75, 100, 112.5, 125, 150, and 175 μl of 10 mM 3XVA solution per 10 ml of nanorod solution (plasmon resonance maxima, respectively, at 886, 863, 840, 802, 788, 751, 727 and 700 nm). Thus, with an increase in the amount of ZHVK, the maximum of plasmon resonance shifts towards shorter wavelengths and its position is determined by the amount of added ZHVK.

FIG. 2 shows the calibration curve of the dependence of the position of the plasmon resonance of gold nanorods on the amount of added 10 mM hydrochloric acid solution per 10 ml of colloid of gold nanorods with an initial concentration. Thus, the adjustment of the position of the PR of gold nanorods is determined by one parameter - the amount of added chloroauric acid.

FIG. Figure 3 shows the time dependences of the position of the plasmon resonance maximum in the extinction spectrum of nanorods after the addition of 147 (1), 220.5 (2), and 294 μL (3) of 10 mM ZHVA solution to 10 ml of colloid. It can be seen that with an increase in the amount of added 3XVA, the shift of the plasmon resonance accelerates in the first 20 min of the reaction. After that, the reaction rate levels off, and the main spectral changes occur within the first 60 minutes. Thus, it was demonstrated that the main shift occurs within 60 minutes, and after 80 minutes, the position of the maximum in the extinction spectrum remains unchanged. As a result, the fact is confirmed that the shift of the plasmon resonance is completely determined by the amount of added ZHVK.

FIG. 4 shows a schematic diagram of selective etching of gold nanorods with gold ions in the presence of CTAB. This scheme explains the selectivity of nanorod etching from the ends. The bilayer of CTAB has a close packing along the long axis of the rod, which prevents the contact of the Au ³⁺ -CTAB complex with the gold surface. On the contrary, at the ends of the rod, the packing of the CTAB bilayer is loose and does not prevent the contact of Au ³⁺ -CTAB with the surface of the rod, which leads to selective etching of the rods from the ends. As a result of this etching, the length of the nanorods is reduced, while the thickness remains unchanged.

FIG. 5 shows photographs of gold nanorods obtained by transmission electron microscopy, which prove that etching occurs along the long axis of the rods and leads to a reduction in their length, while the width and shape of nanorods in the form of cylinders with rounded ends remains unchanged. Initial gold nanorods with PR at 900 nm (a) and gold rods after etching using 25 (b), 100 (c), and 175 (d) μl of 10 mM 3XVA solution per 10 ml of rods solution, which led to their plasmon resonance tuning at 886, 802 and 700 nm, respectively.

Table 1 shows the amount of added ZHVK, length, thickness, axial ratio and wavelength of plasmon resonance of gold nanorods after etching. It can be seen from the presented data that the adjustment of the plasmon resonance wavelength is accompanied by a reduction in the length of the rods and a decrease in their axial ratio, while the thickness of the nanorods practically does not change.

Distinctive features of the proposed solution provide the following advantages:

The method of obtaining gold nanorods with a given position of the plasmon resonance makes it possible to control the PR adjustment due to one parameter - the amount of added ZHVK, which makes it possible to more accurately adjust the PR position.

The method of obtaining gold nanorods with a given position of plasmon resonance is based on selective etching of nanorods with the ZKhVK-CTAB complex along the long axis of the rods and does not contaminate the sample of nanorods with extraneous chemicals.

The method of obtaining gold nanorods with a given position of plasmon resonance makes it possible to obtain samples of nanorods with the same shape and concentration of particles (using the same initial solution of nanorods at the first stage).

Claims (1)

A method of obtaining gold nanorods, including the synthesis of a colloidal solution of gold nanorods in a mixture of cetyltrimethylammonium bromide and sodium oleate with a longitudinal plasmon resonance tuned to the wavelength from the near infrared region of the spectrum, reconstitution in a 100 mM solution of cetyltrimethylammonium bromide colloid solution in gold-hydrochloric acid in an amount from 25 to 1000 μl of 10 mM solution per 10 ml of nanorod colloid.

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