Onset of Intense Surface Enhanced Raman Scattering and Aggregation in the Au@Ag System

Bhatia, Priya; Consiglio, Joseph D.; Diniz, John; Lu, Jia; Hoff, Christopher; Ritz-Schubert, Shelby; Terrill, Roger H.

doi:10.1155/2015/676748

Cited by 3 publications

(22 citation statements)

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“…Ag with the chemical stability and biocompatibility of Au. [37][38][39][40][41][42][43][44][45][46][47][48] Because Ag and Au have nearly identical crystal structures, combining the two metals to prepare hybrid particles is fairly straightforward. Most commonly, Ag and Au are combined by the formation of core-shell structures 41,47,49,50 or by alloying the two metals.…”

Section: Introductionmentioning

confidence: 99%

Dependence of SERS enhancement on the chemical composition and structure of Ag/Au hybrid nanoparticles

Chaffin

O’Connor

Barr

et al. 2016

The Journal of Chemical Physics

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Noble metal nanoparticles (NPs) such as silver (Ag) and gold (Au) have unique plasmonic properties that give rise to surface enhanced Raman scattering (SERS). Generally, Ag NPs have much stronger plasmonic properties and, hence, provide stronger SERS signals than Au NPs. However, Ag NPs lack the chemical stability and biocompatibility of comparable Au NPs and typically exhibit the most intense plasmonic resonance at wavelengths much shorter than the optimal spectral region for many biomedical applications. To overcome these issues, various experimental efforts have been devoted to the synthesis of Ag/Au hybrid NPs for the purpose of SERS detections. However, a complete understanding on how the SERS enhancement depends on the chemical composition and structure of these nanoparticles has not been achieved. In this study, Mie theory and the discrete dipole approximation have been used to calculate the plasmonic spectra and near-field electromagnetic enhancements of Ag/Au hybrid NPs. In particular, we discuss how the electromagnetic enhancement depends on the mole fraction of Au in Ag/Au alloy NPs and how one may use extinction spectra to distinguish between Ag/Au alloyed NPs and Ag-Au core-shell NPs. We also show that for incident laser wavelengths between ∼410 nm and 520 nm, Ag/Au alloyed NPs provide better electromagnetic enhancement than pure Ag, pure Au, or Ag-Au core-shell structured NPs. Finally, we show that silica-core Ag/Au alloy shelled NPs provide even better performance than pure Ag/Au alloy or pure solid Ag and pure solid Au NPs. The theoretical results presented will be beneficial to the experimental efforts in optimizing the design of Ag/Au hybrid NPs for SERS-based detection methods.

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Section: Introductionmentioning

confidence: 99%

Dependence of SERS enhancement on the chemical composition and structure of Ag/Au hybrid nanoparticles

Chaffin

O’Connor

Barr

et al. 2016

The Journal of Chemical Physics

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“…47 Other tests have found that new roughened surfaces, aggregated colloidal suspensions, electrodes, cold substrates, and metal-island films and colloids, silver island films and silver coated beads were appropriate for LSPR enhancement of SERS. 48,[49][50][51][52] PART THREE: THEORY ON SURFACE ANALYSIS…”

Section: Surface Enhanced Raman Scattering (Sers)mentioning

confidence: 99%

“…Equation 3.1.1 shows that the extinction cross section depends on two factors: (1) the dielectric field of the environment and (2) on the volume of the (nano) particle. 51 This is referred to as the long-wavelength approximation of the dipolar resonance. By applying this formula, Mie assumed that the plasmon resonance had to be centered on a light frequency composed by a real part, of a complex dielectric, with twice the magnitude of the dielectric constant of the medium, i.e.…”

Section: Mie Theory and The Raman Scattering Cross Section Of Gold Npsmentioning

confidence: 99%

“…The absolute cross section exhibited by individual molecules in SERS settings can be estimated as is the case with rhodamine 6G (R6G) on nanoparticle aggregates in the Au@Ag system. 50,51 For this purpose, the following knowledge is required: (1) the Most molecules adsorbed to Au@Ag NP aggregates exhibit intense SERS when irradiated at 785 nm. 72,73 This is likely due to the fact that an intense LSPR band that is unique to Au@Ag particle aggregates is formed between 770 and 860 nm.…”

Section: Enhancement Factor From Sers Of Aggregated Au@ag | R6gmentioning

confidence: 99%

“…90 The DLVO theory provides a framework that explains the phenomenon of NP aggregation and at the same time, may be used to determine the SERS phenomena. 50,51 It explains the interaction between small and large size particles, as a deposition process, to a large diameter molecule or a planar substrate. This net energy can be plotted point by point, at each distance, where a curve is drawn by the difference between the small and the larger energy values.…”

Section: Dlvo Theory Of Colloid Interaction Of Aggregated Au@ag Npsmentioning

confidence: 99%

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SERS Intensity Correlations to LSPR on Aggregated Au@Ag Systems

Munera¹

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The optimal surface enhanced Raman scattering (SERS) intensity was correlated to the localized surface plasmon resonance (LSPR) of individual and aggregated gold core/silver shell (Au@Ag) nanoparticles (NPs) in titrations involving the addition of both SERS label (e.g., rhodamine 6G, R6G) and the non-SERS active aggregant (chemical species that triggers the aggregation of NPs) potassium chloride (KCl). Titrating NP solutions with pure SERS label has often resulted in highly non-linear calibrations. In some cases, addition of non-SERS active aggregating agents such as KCl has also resulted in a large increase in SERS signals. An order of initial addition was followed in this report to find any advantage from the initial addition between the SERS label or the aggregant KCl. Interactions between Au@Ag solution and the SERS labels of R6G, 4-mercaptopyridine (MPY) and 4-mercaptobenzoic acid (MBA) were followed using spectrophotometric titrations. Evaluations of the role of aggregation in NP solutions were conducted through the micro-titrations using a quartz cuvette and in two separate stages: (1) a single amount of KCl was followed by increasing amounts of SERS label, and (2) a single amount of SERS label was followed by increasing amounts of KCl. The present reports allowed to conclude that the graphs of SERS intensity (λ EX = 785nm, corrected for solution absorption) versus aggregate absorptions (λ AG = 830 nm) had a correlation between intense SERS and LSPR band extinctions. v ACKNOWLEDGMENTS I want to thank Dr. Terrill, R. for his guidance and support during this project. This report has branched out from his lab where I was able to record, calculate, and analyze these results from the interesting field of nanotechnology. I also want to thank my graduate committee: Dr. Pesek, J. and Dr. Brook, D. who played important roles as supporters and teachers in my organic chemistry labs.

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Rational design of Raman-labeled nanoparticles for a dual-modality, light scattering immunoassay on a polystyrene substrate

et al. 2016

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BackgroundSurface-enhanced Raman scattering (SERS) is a powerful light scattering technique that can be used for sensitive immunoassay development and cell labeling. A major obstacle to using SERS is the complexity of fabricating SERS probes since they require nanoscale characterization and optical uniformity. The light scattering response of SERS probes may also be modulated by the substrate used for SERS analysis. A typical SERS substrate such as quartz can be expensive. Polystyrene is a cheaper substrate option but can decrease the SERS response due to interfering Raman emission peaks and high background fluorescence. The goal of this research is to develop an optimized process for fabricating Raman-labeled nanoparticles for a SERS-based immunoassay on a polystyrene substrate.ResultsWe have developed a method for fabricating SERS nanoparticle probes for use in a light scattering immunoassay on a polystyrene substrate. The light scattering profile of both spherical gold nanoparticle and gold nanorod SERS probes were characterized using Raman spectroscopy and optical absorbance spectroscopy. The effects of substrate interference and autofluorescence were reduced by selecting a Raman reporter with a strong light scattering response in a spectral region where interfering substrate emission peaks are minimized. Both spherical gold nanoparticles and gold nanorods SERS probes used in the immunoassay were detected at labeling concentrations in the low pM range. This analytical sensitivity falls within the typical dynamic range for direct labeling of cell-surface biomarkers using SERS probes.ConclusionSERS nanoparticle probes were fabricated to produce a strong light scattering signal despite substrate interference. The optical extinction and inelastic light scattering of these probes was detected by optical absorbance spectroscopy and Raman spectroscopy, respectively. This immunoassay demonstrates the feasibility of analyzing strongly enhanced Raman signals on polystyrene, which is an inexpensive yet non-ideal Raman substrate. The assay sensitivity, which is in the low pM range, suggests that these SERS probe particles could be used for Raman labeling of cell or tissue samples in a polystyrene tissue culture plate. With continued development, this approach could be used for direct labeling of multiple cell surface biomarkers on strongly interfering substrate platforms.Electronic supplementary materialThe online version of this article (doi:10.1186/s13036-015-0023-y) contains supplementary material, which is available to authorized users.

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Onset of Intense Surface Enhanced Raman Scattering and Aggregation in the Au@Ag System

Cited by 3 publications

References 53 publications

Dependence of SERS enhancement on the chemical composition and structure of Ag/Au hybrid nanoparticles

Dependence of SERS enhancement on the chemical composition and structure of Ag/Au hybrid nanoparticles

SERS Intensity Correlations to LSPR on Aggregated Au@Ag Systems

Rational design of Raman-labeled nanoparticles for a dual-modality, light scattering immunoassay on a polystyrene substrate

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