An official website of the United States government
This work reports on the development of an analyte sampling strategy on a plasmonic substrate to amplify the detection capability of a dual analytical system, paper spray ionization–mass spectrometry (PSI-MS) and surface-enhanced Raman spectroscopy (SERS). While simply applying only an analyte solution to the plasmonic paper results in a limited degree of SERS enhancement, the introduction of plasmonic gold nanoparticles (AuNPs) greatly improves the SERS signals without sacrificing PSI-MS sensitivity. It is initially revealed that the concentration of AuNPs and the type of analytes highly influence the SERS signals and their variations due to the “coffee ring effect” flow mechanism induced during sampling and the degree of the interfacial interactions (e.g., van der Waals, electrostatic, covalent) between the plasmonic substrate and analyte. Subsequent PSI treatment at high voltage conditions further impacts the overall SERS responses, where the signal sensitivity and homogeneity significantly increase throughout the entire substrate, suggesting the ready migration of adsorbed analytes regardless of their interfacial attractive forces. The PSI-induced notable SERS enhancements are presumably associated with creating unique conditions for local aggregation of the AuNPs to induce effective plasmonic couplings and hot spots (i.e., electromagnetic effect) and for repositioning analytes in close proximity to a plasmonic surface to increase polarizability (i.e., chemical effect). The optimized sampling and PSI conditions are also applicable to multi-analyte analysis by SERS and MS, with greatly enhanced detection capability and signal uniformity.
more »
« less
Super-resolution SERS spectral bioimaging
Advances in nanotechnology enable the detection of trace molecules from the enhanced Raman signal generated at the surface of plasmonic nanoparticles. We have developed technology to enable super-resolution imaging of plasmonic nanoparticles, where the fluctuations in the surface enhanced Raman scattering (SERS) signal can be analyzed with localization microscopy techniques to provide nanometer spatial resolution of the emitting molecule’s location. Additional work now enables the super-resolved SERS image and the corresponding spectrum to be acquired simultaneously. Here we will discuss how this approach can be applied to provide new insights into biological cells.
more »
« less
- Award ID(s):
- 2107791
- PAR ID:
- 10414426
- Editor(s):
- Verma, Prabhat; Suh, Yung Doug
- Date Published:
- Journal Name:
- SPIE Nanoscience + Engineering
- Volume:
- 1220304
- Page Range / eLocation ID:
- 1220304-1 - 1220304-6
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Surface-enhanced Raman scattering (SERS) is a sensitive analytical technique capable of magnifying the vibrational intensity of molecules adsorbed onto the surface of metallic nanostructures. Various solution-based SERS-active metallic nanostructures have been designed to generate substantial SERS signal enhancements. However, most of these SERS substrates rely on the chemical aggregation of metallic nanostructures to create strong signals. While this can induce high SERS intensities through plasmonic coupling, most chemically aggregated assemblies suffer from poor signal reproducibility and reduced long-term stability. To overcome these issues, here we report for the first time the synthesis of gold core–satellite nanoparticles (CSNPs) for robust SERS signal generation. The novel CSNP assemblies consist of a 30 nm spherical gold core linked to 18 nm satellite particles via linear heterobifunctional thiol–amine terminated PEG chains. We explore the effects that the varying chain lengths have on SERS hot-spot generation, signal reproducibility and long-term activity. The chain length was varied by using PEGs with different molecular weights (1000 Da, 2000 Da, and 3500 Da). The CSNPs were characterized via UV-Vis spectrophotometry, transmission electron microscopy (TEM), ζ -potential measurements, and lastly SERS measurements. The versatility of the synthesized SERS-active CSNPs was revealed through characterization of optical stability and SERS enhancement at 0, 1, 3, 5, 7 and 14 days.more » « less
-
Chen, Zan (Ed.)Inelastic scattering from molecules because of vibrational modes produces unique Raman shifts, allowing these analytes to be detected with high specificity. Because Raman scattering is weak, surface-enhanced Raman scattering (SERS) has been used as a label-free technique for the detection of a variety of analytes at low concentrations. Using simple solution-based colloidal processing techniques, we have fabricated gold-coated carbon-black nanoparticles that show enhanced Raman activity. By varying the fabrication conditions, we create particles of different surface morphologies, allowing control over the peak wavelength for localized surface plasmon resonance (LSPR). By matching the LSPR wavelength to the incident laser wavelength, we get the highest signal from two model analytes, 4-nitrobenzenethiol (4-NBT) and Congo Red (CR). Our straightforward room temperature solution-based approach for making tunable SERS-active particles expands the range of incident radiation wavelengths that can be used for the detection of analytes using Raman scattering.more » « less
-
Strongly confined electric fields resulting from nanogaps within nanoparticle aggregates give rise to significant enhancement in surface-enhanced Raman scattering (SERS). Nanometer differences in gap sizes lead to drastically different confined field strengths, so much attention has been focused on the development and understanding of nanostructures with controlled gap sizes. In this work, we report a novel petal gap-enhanced Raman tag (GERT) consisting of bipyramid core and a nitrothiophenol (NTP) spacer to support the growth of hundreds of small petals and compare its SERS emission and localization to a traditional bipyramid aggregate. To do this, we used super resolution spectral SERS imaging that simultaneously captures the SERS images and spectra while varying the incident laser polarization. Intensity fluctuations inherent of SERS enabled super resolution algorithms to be applied which revealed sub-diffraction limited differences in the localization with respect to polarization direction for both particles. Interestingly, however, only the traditional bipyramid aggregates experienced a strong polarization dependence in their SERS intensity and in the plasmon-induced conversion of NTP to dimercaptoazobenzene (DMAB), which was localized with nanometer precision to regions of intense electromagnetic fields. The lack of polarization dependence (validated through electromagnetic simulations) and surface reactions from the bipyramid-GERTs suggest that the emissions arising from the bipyramid-GERTs are less influenced by confined fields.more » « less
-
Surface-enhanced Raman scattering (SERS) from gold and silver nanoparticles suspended in solution enables a more quantitative level of analysis relative to SERS from aggregated nanoparticles and roughened metal substrates. This is due to the more predictable and consistent near field enhancement regions created by isolated nanoparticles, and to averaging over the many nanoparticles that diffuse through the excitation beam during the measurement. However, we find that localized heating of the solution by the focused excitation leads to thermophoresis which alters the nanorod concentration in the focal volume and therefore impacts quantitative analysis. Since many phenomena may impact the Raman signal, we record both the Rayleigh and Raman scattering from gold nanoparticle solutions. This allows us to distinguish molecular processes from depletion of nanoparticles in the excitation beam. We observe that the concentration of nanorods can deplete to less than 50% of its original value over 100 second timescale, which are consistent with a thermophoretic effect driving nanoparticles from the beam spot. We also find that the particle motion drives convection within the sample cell that further contributes to signal instabilities.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1117/12.2632824
