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Facile purification of colloidal NIR-responsive gold nanorods using ions assisted self-assembly.

Liu L, Guo Z, Xu L, Xu R, Lu X - Nanoscale Res Lett (2011)

Bottom Line: Therefore, it is essential for the purification of anisotropic gold nanoparticles.The key point of our strategy lies in different shape-dependent solution stability between anisotropic nanoparticles and symmetric ones and selective self-assembly and subsequent precipitation can be induced by introducing ions to the as-made nanorod solution.As a result, gold nanorods of excellent purity (97% in number density) have been obtained within a short time, which has been confirmed by SEM observation and UV-vis-NIR spectroscopy respectively.

View Article: PubMed Central - HTML - PubMed

Affiliation: The Second Affiliated Hospital of Nanjing Medical University, Nanjing 210011, China. luxiang1966@gmail.com.

ABSTRACT
Anisotropic metal nanoparticles have been paid much attention because the broken symmetry of these nanoparticles often leads to novel properties. Anisotropic gold nanoparticles obtained by wet chemical methods inevitably accompany spherical ones due to the intrinsically high symmetry of face-centred cubic metal. Therefore, it is essential for the purification of anisotropic gold nanoparticles. This work presents a facile, low cost while effective solution to the challenging issue of high-purity separation of seed-mediated grown NIR-responsive gold nanorods from co-produced spherical and cubic nanoparticles in solution. The key point of our strategy lies in different shape-dependent solution stability between anisotropic nanoparticles and symmetric ones and selective self-assembly and subsequent precipitation can be induced by introducing ions to the as-made nanorod solution. As a result, gold nanorods of excellent purity (97% in number density) have been obtained within a short time, which has been confirmed by SEM observation and UV-vis-NIR spectroscopy respectively. Based on the experimental facts, a possible shape separation mechanism was also proposed.

No MeSH data available.


Related in: MedlinePlus

Absorption spectra of aqueous solutions. (a) As-made gold NR mixture, (b) purified gold NRs (red curve), and (c) nanoparticles kept in supernatant after purification. The photograph (inset) shows the corresponding colour of NR mixture solution, purified NRs solution and supernatant from left to right
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Figure 2: Absorption spectra of aqueous solutions. (a) As-made gold NR mixture, (b) purified gold NRs (red curve), and (c) nanoparticles kept in supernatant after purification. The photograph (inset) shows the corresponding colour of NR mixture solution, purified NRs solution and supernatant from left to right

Mentions: To further investigate the purity of the separated gold NRs and better assess the efficiency of the present purification strategy, the as-made NR solution, the solution of the NR precipitates and the supernatant after purification were characterized by UV-vis-NIR spectroscopy respectively. For easy comparison, longitudinal plamson band of the purified NRs was normalized to the same intensity of that of the as-made NRs. As shown in Figure 2, the longitudinal plasmon bands of the NRs before and after purification locate at the similar position at 1,015 nm (Figure 2, curve a and b), whereas the transverse plasmon band of the purified NRs turns much narrower and blue shifts from 520 nm to 505 nm. We also observed that the transverse plasmon band of purified NRs turns much weaker than that of as-made NRs, indicating the exclusion of the symmetric nanoparticles. Correspondingly, the colour of the NR solutions also change from red to brown before and after purification due to high or minimal fraction of symmetric nanoparticles (Figure 2, inset). UV-vis-NIR spectrum of the supernatant also shows two plasmon bands: one sharp band at 540 nm and the other broad but weak band at 985 nm, respectively (Figure 2, curve c). The former band can be attributed to the symmetric nanoparticles remained in the supernatant. Since the two plasmon bands are independent of each other, it can therefore be concluded that the latter band is due to the longitudinal plasmon of NRs but not the linear assembly of the symmetric ones [22,23]. Moreover, the very weak intensity of the latter band also clearly reveals that the amount of NRs kept in supernatant is minimal, consistent with the SEM observation (Figure 1c). The above experimental facts confirm that the separated gold NRs are in high purity and the good efficiency of this purification strategy.


Facile purification of colloidal NIR-responsive gold nanorods using ions assisted self-assembly.

Liu L, Guo Z, Xu L, Xu R, Lu X - Nanoscale Res Lett (2011)

Absorption spectra of aqueous solutions. (a) As-made gold NR mixture, (b) purified gold NRs (red curve), and (c) nanoparticles kept in supernatant after purification. The photograph (inset) shows the corresponding colour of NR mixture solution, purified NRs solution and supernatant from left to right
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211191&req=5

Figure 2: Absorption spectra of aqueous solutions. (a) As-made gold NR mixture, (b) purified gold NRs (red curve), and (c) nanoparticles kept in supernatant after purification. The photograph (inset) shows the corresponding colour of NR mixture solution, purified NRs solution and supernatant from left to right
Mentions: To further investigate the purity of the separated gold NRs and better assess the efficiency of the present purification strategy, the as-made NR solution, the solution of the NR precipitates and the supernatant after purification were characterized by UV-vis-NIR spectroscopy respectively. For easy comparison, longitudinal plamson band of the purified NRs was normalized to the same intensity of that of the as-made NRs. As shown in Figure 2, the longitudinal plasmon bands of the NRs before and after purification locate at the similar position at 1,015 nm (Figure 2, curve a and b), whereas the transverse plasmon band of the purified NRs turns much narrower and blue shifts from 520 nm to 505 nm. We also observed that the transverse plasmon band of purified NRs turns much weaker than that of as-made NRs, indicating the exclusion of the symmetric nanoparticles. Correspondingly, the colour of the NR solutions also change from red to brown before and after purification due to high or minimal fraction of symmetric nanoparticles (Figure 2, inset). UV-vis-NIR spectrum of the supernatant also shows two plasmon bands: one sharp band at 540 nm and the other broad but weak band at 985 nm, respectively (Figure 2, curve c). The former band can be attributed to the symmetric nanoparticles remained in the supernatant. Since the two plasmon bands are independent of each other, it can therefore be concluded that the latter band is due to the longitudinal plasmon of NRs but not the linear assembly of the symmetric ones [22,23]. Moreover, the very weak intensity of the latter band also clearly reveals that the amount of NRs kept in supernatant is minimal, consistent with the SEM observation (Figure 1c). The above experimental facts confirm that the separated gold NRs are in high purity and the good efficiency of this purification strategy.

Bottom Line: Therefore, it is essential for the purification of anisotropic gold nanoparticles.The key point of our strategy lies in different shape-dependent solution stability between anisotropic nanoparticles and symmetric ones and selective self-assembly and subsequent precipitation can be induced by introducing ions to the as-made nanorod solution.As a result, gold nanorods of excellent purity (97% in number density) have been obtained within a short time, which has been confirmed by SEM observation and UV-vis-NIR spectroscopy respectively.

View Article: PubMed Central - HTML - PubMed

Affiliation: The Second Affiliated Hospital of Nanjing Medical University, Nanjing 210011, China. luxiang1966@gmail.com.

ABSTRACT
Anisotropic metal nanoparticles have been paid much attention because the broken symmetry of these nanoparticles often leads to novel properties. Anisotropic gold nanoparticles obtained by wet chemical methods inevitably accompany spherical ones due to the intrinsically high symmetry of face-centred cubic metal. Therefore, it is essential for the purification of anisotropic gold nanoparticles. This work presents a facile, low cost while effective solution to the challenging issue of high-purity separation of seed-mediated grown NIR-responsive gold nanorods from co-produced spherical and cubic nanoparticles in solution. The key point of our strategy lies in different shape-dependent solution stability between anisotropic nanoparticles and symmetric ones and selective self-assembly and subsequent precipitation can be induced by introducing ions to the as-made nanorod solution. As a result, gold nanorods of excellent purity (97% in number density) have been obtained within a short time, which has been confirmed by SEM observation and UV-vis-NIR spectroscopy respectively. Based on the experimental facts, a possible shape separation mechanism was also proposed.

No MeSH data available.


Related in: MedlinePlus