Au nanoparticles for SERS: Temperature-controlled nanoparticle morphologies and their Raman enhancing properties (original) (raw)
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Quasi-fractal Gold Nanoparticles for Sers: Effect of Nanoparticle Morphology and Concentration
Quasi-fractal gold nanoparticles can be synthesized via a modified and temperature controlled procedure initially used for the synthesis of star-like gold nanoparticles. The surface features of nanoparticles leads to improved enhancement of Raman scattering intensity of analyte molecules due to the increased number of sharp surface features possessing numerous localized surface plasmon resonances (LSPR). The LSPR is affected by the size and shape of surface features as well as inter-nanoparticle interactions, as these affect the oscillation modes of electrons on the nanoparticle surfaces. The effect of the particle morphologies on the LSPR and further on the surface-enhancing capabilities of these nanoparticles is explored by comparing different nanoparticle morphologies and concentrations. We show that in a fixed nanoparticle concentration regime, Quasi-fractal gold nanoparticles provide the highest level of surface enhancement, whereas spherical nanoparticles provide the largest enhancement in a fixed gold concentration regime. The presence of highly branched features enables these nanoparticles to couple with a laser wavelength despite having no strong absorption band and hence no single surface plasmon resonance. This cumulative LSPR may allow these nanoparticle to be used in a variety of applications where laser wavelength flexibility is beneficial, such as in medical imaging applications where fluorescence at short laser wavelengths may be coupled with non-fluorescing long laser wavelengths for molecular sensing.
Self-assembled large Au nanoparticle arrays with regular hot spots for SERS
Small, 2011
The cost-effective self-assembly of 80 nm Au nanoparticles (NPs) into large-domain, hexagonally close-packed arrays for high-sensitivity and high-fi delity surfaceenhanced Raman spectroscopy (SERS) is demonstrated. These arrays exhibit specifi c optical resonances due to strong interparticle coupling, which are well reproduced by fi nite-difference time-domain (FDTD) simulations. The gaps between NPs form a regular lattice of hot spots that enable a large amplifi cation of both photoluminescence and Raman signals. At smaller wavelengths the hot spots are extended away from the minimum-gap positions, which allows SERS of larger analytes that do not fi t into small gaps. Using CdSe quantum dots (QDs) a 3-5 times larger photoluminescence enhancement than previously reported is experimentally demonstrated and an unambiguous estimate of the electromagnetic SERS enhancement factor of ≈ 10 4 is obtained by direct scanning electron microscopy imaging of QDs responsible for the Raman signal. Much stronger enhancement of ≈ 10 8 is obtained at larger wavelengths for benzenethiol molecules penetrating the NP gaps. SERS Substrates A. Chen et al. 2366 www.small-journal.com
Multimodal Gold Nanoprobes for SERS Bioimaging
Journal of Nanomedicine & Nanotechnology, 2015
Growing number of studies report on the improved sensitivity of various imaging modalities in detecting abnormalities within tumours. Surface enhanced Raman scattering (SERS) microscopy is a novel optical imaging technique which is advantageous in terms of greater multiplexing capability, minimal or no photobleaching of the Raman reporters, better spatial resolution and low signal-to-noise ratio within complex biological environment. For the enhancement of the Raman vibrational signal in SERS bioimaging, gold nanoparticles (GNP) are the most viable among metal nanoparticles because of comparable ease in controlling its size distribution and biocompatibility, among other parameters. GNP based SERS nanoprobes can be synthesised by tagging Raman reporter and conjugating with target specific biomolecules. Because of GNP's wide-ranging optical properties and narrow and distinct signal from SERS, other labelling methodologies like fluorescence microscopy, magnetic resonance imaging (MRI), etc. can also be implemented along with SERS bioimaging, by tagging fluorophores, magnetic nanoparticles, etc. This review focuses on various structures and shapes of GNP, fabricating GNP based nanoprobes and the multiplexing and multi-modality capability of GNP based SERS nanoprobes.
Journal of Nanobiotechnology, 2022
Background: To take advantages, such as multiplex capacity, non-photobleaching property, and high sensitivity, of surface-enhanced Raman scattering (SERS)-based in vivo imaging, development of highly enhanced SERS nanoprobes in near-infrared (NIR) region is needed. A well-controlled morphology and biocompatibility are essential features of NIR SERS nanoprobes. Gold (Au)-assembled nanostructures with controllable nanogaps with highly enhanced SERS signals within multiple hotspots could be a breakthrough. Results: Au-assembled silica (SiO 2) nanoparticles (NPs) (SiO 2 @Au@Au NPs) as NIR SERS nanoprobes are synthesized using the seed-mediated growth method. SiO 2 @Au@Au NPs using six different sizes of Au NPs (SiO 2 @Au@Au 50-SiO 2 @Au@Au 500) were prepared by controlling the concentration of Au precursor in the growth step. The nanogaps between Au NPs on the SiO 2 surface could be controlled from 4.16 to 0.98 nm by adjusting the concentration of Au precursor (hence increasing Au NP sizes), which resulted in the formation of effective SERS hotspots. SiO 2 @Au@Au 500 NPs with a 0.98-nm gap showed a high SERS enhancement factor of approximately 3.8 × 10 6 under 785-nm photoexcitation. SiO 2 @Au@Au 500 nanoprobes showed detectable in vivo SERS signals at a concentration of 16 μg/mL in animal tissue specimen at a depth of 7 mm. SiO 2 @Au@Au 500 NPs with 14 different Raman label compounds exhibited distinct SERS signals upon subcutaneous injection into nude mice. Conclusions: SiO 2 @Au@Au NPs showed high potential for in vivo applications as multiplex nanoprobes with high SERS sensitivity in the NIR region.
Gold nanoparticles as a substrate in bio-analytical near-infrared surface-enhanced Raman scattering
The Analyst, 2015
As biospectroscopy techniques continue to be developed for screening or diagnosis within a point-of-care setting, an important development for this field will be high-throughput optimization. For many of these techniques, it is therefore necessary to adapt and develop parameters to generate a robust yet simple approach delivering high-quality spectra from biological samples. Specifically, this is important for surface-enhanced Raman spectroscopy (SERS) wherein there are multiple variables that can be optimised to achieve an enhancement of the Raman signal from a sample. One hypothesis is that "large" diameter (>100 nm) gold nanoparticles provide a greater enhancement at near-infrared (NIR) and infrared (IR) wavelengths than those <100 nm in diameter. Herein, we examine this notion using examples in which SERS spectra were acquired from MCF-7 breast cancer cells incubated with 150 nm gold nanoparticles. It was found that 150 nm gold nanoparticles are an excellent material for NIR/IR SERS. Larger gold nanoparticles may better satisfy the theoretical restraints for SERS enhancement at NIR/IR wavelengths compared to smaller nanoparticles. Also, larger nanoparticles or their aggregates are more readily observed via optical microscopy (and especially electron microscopy) compared to smaller ones. This allows rapid and straightforward identification of target areas containing a high concentration of nanoparticles and facilitating SERS spectral acquisition. To some extent, these observations appear to extend to biofluids such as blood plasma or (especially) serum; SERS spectra of such biological samples often exhibit a low signal-to-noise ratio in the absence of nanoparticles. With protein-rich biofluids such as serum, a dramatic SERS effect can be observed; although this might facilitate improved spectral biomarker identification in the future, it may not always improve classification between control vs. cancer. Thus, use of "large" gold nanoparticles are a good starting point in order to derive informative NIR/IR SERS analysis of biological samples.
Physical Chemistry Chemical Physics, 2017
We used a combination of Raman microscopy, AFM and TEM to quantify the influence of dimerization on the surface enhanced Raman spectroscopy (SERS) signal for gold and silver nanoparticles (NPs) modified with Raman reporters and situated on gold, silver, and aluminum films and a silicon wafer. The overall increases in the mean SERS enhancement factor (EF) upon dimerization (up by 43% on average) and trimerisation (up by 96% on average) of AuNPs and AgNPs on the studied metal films are within a factor of two, which is moderate when compared to most theoretical models. However, the maximum ratio of EFs for some dimers to the mean EF of monomers can be as high as 5.5 for AgNPs on a gold substrate. In contrast, for dimerization and trimerization of gold and silver NPs on silicon, the mean EF increases by 1-2 orders of magnitude relative to the mean EF of single NPs. Therefore, hot spots in the interparticle gap between gold nanoparticles rather than hot spots between Au nanoparticles and the substrate dominate SERS enhancement for dimers and trimers on a silicon substrate. However, Raman labeled noble metal nanoparticles on plasmonic metal films generate on average SERS enhancement of the same order of magnitude for both types of hot spot zones (e.g. NP/NP and NP/metal film).
Synthesis and SERS Application of SiO2@Au Nanoparticles
Plasmonics, 2014
In this letter, we report a chemical route for synthesizing SiO 2 @Au core-shell nanoparticles. The process includes four steps: i) preparation of the silica cores, ii) grafting gold nanoparticles over SiO 2 cores, iii) priming of the silica-coated gold nanoparticles with 2 and 10 nm gold colloids and finally iv) formation of complete shell. The optical extinction spectra were experimentally measured and compared to numerical calculations in order to confirm the dimensions deduced from SEM images. Finally, the potential of such coreshell nanoparticles for biosensing was probed by means of Surface Enhanced Raman Scattering measurements and revealed higher sensitivities with much lower gold quantity of such core-shell nanoparticles compared to Au nanoparticles exhibiting similar diameters.
Resizing of Colloidal Gold Nanorods and Morphological Probing by SERS
The Journal of Physical Chemistry C, 2013
We demonstrate that surface-enhanced Raman scattering (SERS) spectroscopy can be used to monitor variations in the aspect ratio (AR) of colloidal gold nanorods (NRs) during a chemical etching process. The AR of colloidal Au NRs prepared by a seed method was deliberately decreased by addition of aqueous K 2 S 2 O 8 . SERS studies using a 1064 nm laser line revealed a decrease on the detection sensitivity as the nanorods became shorter and using the anion diethyldithiocarbamate (DTC) as the analytical probe. The morphological changes observed for distinct reaction times have also been confirmed by TEM and optical measurements. The dependence of the SERS sensitivity observed for Au NRs of variable AR has been investigated either by using colloids submitted to etching at distinct reaction temperatures or by using a distinct excitation laser line. Therefore, this spectroscopic method offers the possibility to probe in situ changes on the AR of colloidal Au NRs in analytical contexts in which other techniques cannot be easily implemented.