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The characteristic Ag(core)Au(shell) nanoparticles as SERS substrates in detecting dopamine molecules at various pH ranges.

Bu Y, Lee SW - Int J Nanomedicine (2015)

Bottom Line: When the pH of the solution was acidic (pH <5) or basic (pH >9), the AgcoreAushell NPs exhibited negligible SERS activity toward the DA molecules, due to the weakened interactions (or repulsive forces) between the DA molecules and the core-shell NPs.On the other hand, the AgcoreAushell NPs exhibited a high SERS activity in the intermediate pH ranges (pH 7-9), due to the molecular bridging effect of DA molecules, which allows probe molecules to be located at the interstitial junctions (so-called hot spots) between the core-shell NPs.The results of this study highlight the importance of probe-induced clustering of core-shell NPs in the SERS measurements at physiological pH.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical Engineering, Faculty of Engineering, Monash University, Melbourne, VIC, Australia.

ABSTRACT
AgcoreAushell nanoparticles (NPs) are a promising surface-enhanced Raman scattering (SERS) substrate, which can offer a high enhancement factor through the combined effect of the high SERS activity of the Ag core and the biocompatibility of the Au shell. In this study, AgcoreAushell NPs were examined as SERS substrates for the sensitive detection of dopamine (DA) molecules in an aqueous solution. The SERS activity of the AgcoreAushell NPs was strongly dependent on the pH of the solution. When the pH of the solution was acidic (pH <5) or basic (pH >9), the AgcoreAushell NPs exhibited negligible SERS activity toward the DA molecules, due to the weakened interactions (or repulsive forces) between the DA molecules and the core-shell NPs. On the other hand, the AgcoreAushell NPs exhibited a high SERS activity in the intermediate pH ranges (pH 7-9), due to the molecular bridging effect of DA molecules, which allows probe molecules to be located at the interstitial junctions (so-called hot spots) between the core-shell NPs. The results of this study highlight the importance of probe-induced clustering of core-shell NPs in the SERS measurements at physiological pH.

No MeSH data available.


Related in: MedlinePlus

Physico-chemical properties of core-shell AgcoreAushell NPs.Notes: (A) The UV-vis spectra of AgcoreAushell NPs (38 nm) at various pH ranges. (B) The UV-vis spectra of AgcoreAushell NPs with DA (10−4 M) at various pH ranges. (C) The absorption maximum of AgcoreAushell NPs with and without DA (10−4 M) at various pH ranges. (D) The particle size of AgcoreAushell NPs with and without DA (10−4 M) at various pH ranges.Abbreviations: au, arbitrary unit; DA, dopamine; NPs, nanoparticles; UV-vis, ultraviolet-visible.
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f4-ijn-10-047: Physico-chemical properties of core-shell AgcoreAushell NPs.Notes: (A) The UV-vis spectra of AgcoreAushell NPs (38 nm) at various pH ranges. (B) The UV-vis spectra of AgcoreAushell NPs with DA (10−4 M) at various pH ranges. (C) The absorption maximum of AgcoreAushell NPs with and without DA (10−4 M) at various pH ranges. (D) The particle size of AgcoreAushell NPs with and without DA (10−4 M) at various pH ranges.Abbreviations: au, arbitrary unit; DA, dopamine; NPs, nanoparticles; UV-vis, ultraviolet-visible.

Mentions: Figure 4A and B demonstrates the pH-dependent changes in the UV-vis spectra of the AgcoreAushell NPs (38 nm) in the absence or presence of DA molecules. As the solution pH increases without DA molecules, the plasmon band of the AgcoreAushell NPs is gradually blue-shifted. This shift indicates the collapse of the partial aggregation into monodispersed core–shell NPs, which is attributed to repulsive interactions between the core–shell NPs (Figure 4A). In the presence of DA molecules (10−4 M), the AgcoreAushell NPs also exhibit a blue-shift in the primary absorption bands when the pH changed from pH 3 to pH 5, as shown in Figure 4B. At the intermediate pH ranges (pH 7–9), however, the presence of DA molecules induces the aggregation of core–shell NPs and thereby generates a secondary peak at a longer wavelength (>650 nm) attributed to the plasmon coupling of aggregated particles.38,39 A further increase in the solution pH again induces a blue-shift of the primary absorption band with the simultaneous disappearance of the secondary peak at the longer wavelength, due to the repulsive dispersion of core–shell NPs.


The characteristic Ag(core)Au(shell) nanoparticles as SERS substrates in detecting dopamine molecules at various pH ranges.

Bu Y, Lee SW - Int J Nanomedicine (2015)

Physico-chemical properties of core-shell AgcoreAushell NPs.Notes: (A) The UV-vis spectra of AgcoreAushell NPs (38 nm) at various pH ranges. (B) The UV-vis spectra of AgcoreAushell NPs with DA (10−4 M) at various pH ranges. (C) The absorption maximum of AgcoreAushell NPs with and without DA (10−4 M) at various pH ranges. (D) The particle size of AgcoreAushell NPs with and without DA (10−4 M) at various pH ranges.Abbreviations: au, arbitrary unit; DA, dopamine; NPs, nanoparticles; UV-vis, ultraviolet-visible.
© Copyright Policy
Related In: Results  -  Collection

License
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getmorefigures.php?uid=PMC4554420&req=5

f4-ijn-10-047: Physico-chemical properties of core-shell AgcoreAushell NPs.Notes: (A) The UV-vis spectra of AgcoreAushell NPs (38 nm) at various pH ranges. (B) The UV-vis spectra of AgcoreAushell NPs with DA (10−4 M) at various pH ranges. (C) The absorption maximum of AgcoreAushell NPs with and without DA (10−4 M) at various pH ranges. (D) The particle size of AgcoreAushell NPs with and without DA (10−4 M) at various pH ranges.Abbreviations: au, arbitrary unit; DA, dopamine; NPs, nanoparticles; UV-vis, ultraviolet-visible.
Mentions: Figure 4A and B demonstrates the pH-dependent changes in the UV-vis spectra of the AgcoreAushell NPs (38 nm) in the absence or presence of DA molecules. As the solution pH increases without DA molecules, the plasmon band of the AgcoreAushell NPs is gradually blue-shifted. This shift indicates the collapse of the partial aggregation into monodispersed core–shell NPs, which is attributed to repulsive interactions between the core–shell NPs (Figure 4A). In the presence of DA molecules (10−4 M), the AgcoreAushell NPs also exhibit a blue-shift in the primary absorption bands when the pH changed from pH 3 to pH 5, as shown in Figure 4B. At the intermediate pH ranges (pH 7–9), however, the presence of DA molecules induces the aggregation of core–shell NPs and thereby generates a secondary peak at a longer wavelength (>650 nm) attributed to the plasmon coupling of aggregated particles.38,39 A further increase in the solution pH again induces a blue-shift of the primary absorption band with the simultaneous disappearance of the secondary peak at the longer wavelength, due to the repulsive dispersion of core–shell NPs.

Bottom Line: When the pH of the solution was acidic (pH <5) or basic (pH >9), the AgcoreAushell NPs exhibited negligible SERS activity toward the DA molecules, due to the weakened interactions (or repulsive forces) between the DA molecules and the core-shell NPs.On the other hand, the AgcoreAushell NPs exhibited a high SERS activity in the intermediate pH ranges (pH 7-9), due to the molecular bridging effect of DA molecules, which allows probe molecules to be located at the interstitial junctions (so-called hot spots) between the core-shell NPs.The results of this study highlight the importance of probe-induced clustering of core-shell NPs in the SERS measurements at physiological pH.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical Engineering, Faculty of Engineering, Monash University, Melbourne, VIC, Australia.

ABSTRACT
AgcoreAushell nanoparticles (NPs) are a promising surface-enhanced Raman scattering (SERS) substrate, which can offer a high enhancement factor through the combined effect of the high SERS activity of the Ag core and the biocompatibility of the Au shell. In this study, AgcoreAushell NPs were examined as SERS substrates for the sensitive detection of dopamine (DA) molecules in an aqueous solution. The SERS activity of the AgcoreAushell NPs was strongly dependent on the pH of the solution. When the pH of the solution was acidic (pH <5) or basic (pH >9), the AgcoreAushell NPs exhibited negligible SERS activity toward the DA molecules, due to the weakened interactions (or repulsive forces) between the DA molecules and the core-shell NPs. On the other hand, the AgcoreAushell NPs exhibited a high SERS activity in the intermediate pH ranges (pH 7-9), due to the molecular bridging effect of DA molecules, which allows probe molecules to be located at the interstitial junctions (so-called hot spots) between the core-shell NPs. The results of this study highlight the importance of probe-induced clustering of core-shell NPs in the SERS measurements at physiological pH.

No MeSH data available.


Related in: MedlinePlus