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Gold Nanowire Forests for SERS Detection.

La Porta A, Grzelczak M, Liz-Marzán LM - ChemistryOpen (2014)

Bottom Line: This allowed us to select the optimum conditions for maximum electromagnetic enhancement and performance in surface enhanced Raman scattering (SERS) detection.SERS measurements confirmed the uniform and reproducible distribution of the nanowires on the substrate, with the subsequent high reproducibility of hot spot formation.Detection of malachite green in water and of 1-naphthalenethiol from the gas phase are demonstrated as proof-of-concept applications of these three-dimensional SERS substrates.

View Article: PubMed Central - PubMed

Affiliation: Bionanoplasmonics Laboratory, CIC biomaGUNE Paseo de Miramón 182, 20009 Donostia-San Sebastián (Spain) E-mail: llizmarzan@cicbiomagune.es.

ABSTRACT
Simple wet chemistry has been applied to control the vertical growth of gold nanowires on a glass substrate. As a consequence, the longitudinal localized surface plasmon band position can be tuned from 656 to 1477 nm in a few minutes by simply controlling the growth rate and time. This allowed us to select the optimum conditions for maximum electromagnetic enhancement and performance in surface enhanced Raman scattering (SERS) detection. SERS measurements confirmed the uniform and reproducible distribution of the nanowires on the substrate, with the subsequent high reproducibility of hot spot formation. Detection of malachite green in water and of 1-naphthalenethiol from the gas phase are demonstrated as proof-of-concept applications of these three-dimensional SERS substrates.

No MeSH data available.


Related in: MedlinePlus

A) Absorbance spectra of Au NWs for different growth times as labeled (min). B) Wavelength of the maximum of the lower energy plasmon band, as a function of growth time. Each point is the result of an average over three different substrates, and the error bar indicates high synthesis reproducibility. C–E) SEM images of Au NWs on glass after 3 (C), 7 (D) and 10 min (E). F–H) Corresponding TEM images of Au NWs from the same substrates. All scale bars represent 50 nm.
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fig01: A) Absorbance spectra of Au NWs for different growth times as labeled (min). B) Wavelength of the maximum of the lower energy plasmon band, as a function of growth time. Each point is the result of an average over three different substrates, and the error bar indicates high synthesis reproducibility. C–E) SEM images of Au NWs on glass after 3 (C), 7 (D) and 10 min (E). F–H) Corresponding TEM images of Au NWs from the same substrates. All scale bars represent 50 nm.

Mentions: The growth of vertical Au NWs on glass substrates was based on the method recently reported by He et al.35 This method comprises three steps: glass functionalization with an aminosilane (3-aminopropyltriethoxy silane, APTES), seed self-assembly and seeded growth. The key element behind the preferential anisotropic growth perpendicular to the substrate seems to be the use of MBA to functionalize the Au NP seeds upper surface, which is not possible on the lower part because of the presence of APTES binding the NP to the glass surface. This results in the reduction of AuIII only at the bottom side of the seeds, which acts as catalysts. As a consequence, each seed is lifted up from the glass, and the reduced gold atoms are covered by MBA molecules present in solution, thereby forcing the reduction to occur always at the bottom side. Whereas the diameter of the NWs depends on the ratio between MBA and AuIII in solution, their length can be readily controlled through the growth time. The resulting increase in the aspect ratio was readily observed through changes in the Vis/NIR spectra (Figure 1A). As the NWs grow longer, redshift and broadening are observed in the plasmon band, with a new band developing after 4–5 min. After 10 min of NW growth, two distinct bands can be discerned, one centered around 600 nm and a broader one around 1500 nm. Although the bands become very broad after Au NW growth, this process proved to be highly reproducible, as shown in Figure 1B, where the maximum positions of the low-energy bands are plotted versus growth time for three different synthesis series, each comprising seven substrates that were grown for different times. The LSPR spectra in Figure 1A are the result of plasmon coupling between individual NWs. Interestingly, the LSPR of (non-coupled) NWs in solution (not shown) shows a red-shifted longitudinal band, which is in agreement with the results by Funston et al.36 for side-by-side aligned nanorods. The NW substrate used in our work can be considered as many side-by-side aligned NWs, so that by changing the growth time, it is possible to control not only the LSPR of the individual NWs but also their collective coupling behavior. It is important to highlight that the growth solution used for the synthesis always consisted of freshly prepared MBA and ascorbic acid stock solutions, meaning that changes arising from potential errors in this preliminary step do not appear to affect NW growth. From Figure 1A it is however not perfectly clear at which point of the synthesis the nanowire shape starts to develop. Indeed, for growth times up to 3 min a single plasmon band is visible in the spectrum. Transmission electron microscopy (TEM) was used to analyze the formed particles, upon detachment from the substrate (see Experimental Section for details). The electron micrographs show that already after one minute of growth, anisotropic nanoparticles are formed but with rather undefined shapes (Figure S1, Supporting Information). After 2 min, the aspect ratio has increased and a rod-like morphology is clearly observed; whereas after 3 min, NWs have definitely been formed. Systematic experiments (data not shown) evidenced that the growth rate can be controlled by varying the amounts of AuIII and MBA in the growth solution while keeping a constant molar ratio between them. Another important factor influencing the overall growth rate is the number of seeds acting as catalysts: at fixed [AuIII]/[MBA] ratio, increasing the seed density on the substrate leads to slower NW growth because of a lower amount of AuIII per seed. This is an important issue in terms of reproducibility in NW length. Figures 1C–E show scanning electron microscopy (SEM) images of three substrates grown for 3, 7 and 10 min, displaying the resulting density of NWs on the glass substrate as well as their tendency to bend and form bundles. Details about the dimensions were obtained from TEM images as shown in Figures 1f–H. The average diameter does not vary during growth and is determined by the MBA/AuIII molar ratio in the growth solution (0.48 in these samples), and it was determined to be 5.34±0.76 nm. A statistical analysis reveals that after 3, 7 and 10 min the NW lengths are 68±9, 198±26 and 334±47 nm, respectively.


Gold Nanowire Forests for SERS Detection.

La Porta A, Grzelczak M, Liz-Marzán LM - ChemistryOpen (2014)

A) Absorbance spectra of Au NWs for different growth times as labeled (min). B) Wavelength of the maximum of the lower energy plasmon band, as a function of growth time. Each point is the result of an average over three different substrates, and the error bar indicates high synthesis reproducibility. C–E) SEM images of Au NWs on glass after 3 (C), 7 (D) and 10 min (E). F–H) Corresponding TEM images of Au NWs from the same substrates. All scale bars represent 50 nm.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4232270&req=5

fig01: A) Absorbance spectra of Au NWs for different growth times as labeled (min). B) Wavelength of the maximum of the lower energy plasmon band, as a function of growth time. Each point is the result of an average over three different substrates, and the error bar indicates high synthesis reproducibility. C–E) SEM images of Au NWs on glass after 3 (C), 7 (D) and 10 min (E). F–H) Corresponding TEM images of Au NWs from the same substrates. All scale bars represent 50 nm.
Mentions: The growth of vertical Au NWs on glass substrates was based on the method recently reported by He et al.35 This method comprises three steps: glass functionalization with an aminosilane (3-aminopropyltriethoxy silane, APTES), seed self-assembly and seeded growth. The key element behind the preferential anisotropic growth perpendicular to the substrate seems to be the use of MBA to functionalize the Au NP seeds upper surface, which is not possible on the lower part because of the presence of APTES binding the NP to the glass surface. This results in the reduction of AuIII only at the bottom side of the seeds, which acts as catalysts. As a consequence, each seed is lifted up from the glass, and the reduced gold atoms are covered by MBA molecules present in solution, thereby forcing the reduction to occur always at the bottom side. Whereas the diameter of the NWs depends on the ratio between MBA and AuIII in solution, their length can be readily controlled through the growth time. The resulting increase in the aspect ratio was readily observed through changes in the Vis/NIR spectra (Figure 1A). As the NWs grow longer, redshift and broadening are observed in the plasmon band, with a new band developing after 4–5 min. After 10 min of NW growth, two distinct bands can be discerned, one centered around 600 nm and a broader one around 1500 nm. Although the bands become very broad after Au NW growth, this process proved to be highly reproducible, as shown in Figure 1B, where the maximum positions of the low-energy bands are plotted versus growth time for three different synthesis series, each comprising seven substrates that were grown for different times. The LSPR spectra in Figure 1A are the result of plasmon coupling between individual NWs. Interestingly, the LSPR of (non-coupled) NWs in solution (not shown) shows a red-shifted longitudinal band, which is in agreement with the results by Funston et al.36 for side-by-side aligned nanorods. The NW substrate used in our work can be considered as many side-by-side aligned NWs, so that by changing the growth time, it is possible to control not only the LSPR of the individual NWs but also their collective coupling behavior. It is important to highlight that the growth solution used for the synthesis always consisted of freshly prepared MBA and ascorbic acid stock solutions, meaning that changes arising from potential errors in this preliminary step do not appear to affect NW growth. From Figure 1A it is however not perfectly clear at which point of the synthesis the nanowire shape starts to develop. Indeed, for growth times up to 3 min a single plasmon band is visible in the spectrum. Transmission electron microscopy (TEM) was used to analyze the formed particles, upon detachment from the substrate (see Experimental Section for details). The electron micrographs show that already after one minute of growth, anisotropic nanoparticles are formed but with rather undefined shapes (Figure S1, Supporting Information). After 2 min, the aspect ratio has increased and a rod-like morphology is clearly observed; whereas after 3 min, NWs have definitely been formed. Systematic experiments (data not shown) evidenced that the growth rate can be controlled by varying the amounts of AuIII and MBA in the growth solution while keeping a constant molar ratio between them. Another important factor influencing the overall growth rate is the number of seeds acting as catalysts: at fixed [AuIII]/[MBA] ratio, increasing the seed density on the substrate leads to slower NW growth because of a lower amount of AuIII per seed. This is an important issue in terms of reproducibility in NW length. Figures 1C–E show scanning electron microscopy (SEM) images of three substrates grown for 3, 7 and 10 min, displaying the resulting density of NWs on the glass substrate as well as their tendency to bend and form bundles. Details about the dimensions were obtained from TEM images as shown in Figures 1f–H. The average diameter does not vary during growth and is determined by the MBA/AuIII molar ratio in the growth solution (0.48 in these samples), and it was determined to be 5.34±0.76 nm. A statistical analysis reveals that after 3, 7 and 10 min the NW lengths are 68±9, 198±26 and 334±47 nm, respectively.

Bottom Line: This allowed us to select the optimum conditions for maximum electromagnetic enhancement and performance in surface enhanced Raman scattering (SERS) detection.SERS measurements confirmed the uniform and reproducible distribution of the nanowires on the substrate, with the subsequent high reproducibility of hot spot formation.Detection of malachite green in water and of 1-naphthalenethiol from the gas phase are demonstrated as proof-of-concept applications of these three-dimensional SERS substrates.

View Article: PubMed Central - PubMed

Affiliation: Bionanoplasmonics Laboratory, CIC biomaGUNE Paseo de Miramón 182, 20009 Donostia-San Sebastián (Spain) E-mail: llizmarzan@cicbiomagune.es.

ABSTRACT
Simple wet chemistry has been applied to control the vertical growth of gold nanowires on a glass substrate. As a consequence, the longitudinal localized surface plasmon band position can be tuned from 656 to 1477 nm in a few minutes by simply controlling the growth rate and time. This allowed us to select the optimum conditions for maximum electromagnetic enhancement and performance in surface enhanced Raman scattering (SERS) detection. SERS measurements confirmed the uniform and reproducible distribution of the nanowires on the substrate, with the subsequent high reproducibility of hot spot formation. Detection of malachite green in water and of 1-naphthalenethiol from the gas phase are demonstrated as proof-of-concept applications of these three-dimensional SERS substrates.

No MeSH data available.


Related in: MedlinePlus