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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

The aggregation behavior of AgcoreAushell NPs with and without DA molecules at various pH ranges.Abbreviations: DA, dopamine; NPs, nanoparticles.
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f6-ijn-10-047: The aggregation behavior of AgcoreAushell NPs with and without DA molecules at various pH ranges.Abbreviations: DA, dopamine; NPs, nanoparticles.

Mentions: Figure 6 illustrates the pH-dependent interaction of the AgcoreAushell NPs with DA molecules at various pH ranges: i) at low pH levels (pH <5), the AgcoreAushell NPs are less negatively charged because of the neutralization effect by the hydrogen ions, ie, the zeta potential of the NPs is −8.58±8.42 mV at pH 3. Thus, the cross-linking effect of adsorbed DA is fairly weakened, resulting in a slight aggregation of core–shell NPs. ii) At an intermediate pH range (pH 7–9), the AgcoreAushell NPs are more negatively charged and the DA is positively charged, inducing electrostatic interactions between the AgcoreAushell NPs and the DA molecules. Thus, DA molecules are effectively adsorbed on the AgcoreAushell NPs as cross-linkers which can enhance the SERS signals by providing effective hot spots at the interstitial junctions between the core–shell NPs. iii) At high pH levels (pH >9), the DA presents in neutral or negatively charged states, ie, the zeta potential of the NPs is −45.68±14.75 mV at pH 10. Thus, DA adsorption is significantly reduced owing to the repulsive interactions against the negatively charged 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)

The aggregation behavior of AgcoreAushell NPs with and without DA molecules at various pH ranges.Abbreviations: DA, dopamine; NPs, nanoparticles.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4554420&req=5

f6-ijn-10-047: The aggregation behavior of AgcoreAushell NPs with and without DA molecules at various pH ranges.Abbreviations: DA, dopamine; NPs, nanoparticles.
Mentions: Figure 6 illustrates the pH-dependent interaction of the AgcoreAushell NPs with DA molecules at various pH ranges: i) at low pH levels (pH <5), the AgcoreAushell NPs are less negatively charged because of the neutralization effect by the hydrogen ions, ie, the zeta potential of the NPs is −8.58±8.42 mV at pH 3. Thus, the cross-linking effect of adsorbed DA is fairly weakened, resulting in a slight aggregation of core–shell NPs. ii) At an intermediate pH range (pH 7–9), the AgcoreAushell NPs are more negatively charged and the DA is positively charged, inducing electrostatic interactions between the AgcoreAushell NPs and the DA molecules. Thus, DA molecules are effectively adsorbed on the AgcoreAushell NPs as cross-linkers which can enhance the SERS signals by providing effective hot spots at the interstitial junctions between the core–shell NPs. iii) At high pH levels (pH >9), the DA presents in neutral or negatively charged states, ie, the zeta potential of the NPs is −45.68±14.75 mV at pH 10. Thus, DA adsorption is significantly reduced owing to the repulsive interactions against the negatively charged 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