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Silica shell coatings, which constitute important technology for nanoparticle (NP) developments, are utilized in many applications. The silica shell's thickness greatly affects distance-dependent optical properties, such as metal-enhanced fluorescence (MEF) and fluorescence quenching in plasmonic nanocomposites. However, the precise control of silica-shell thicknesses has been mainly conducted on single metal NPs, and rarely on complex nanocomposites. In this study, silica shell-coated Ag nanoparticle-assembled silica nanoparticles (SiO2@Ag@SiO2), with finely controlled silica shell thicknesses (4 nm to 38 nm), were prepared, and quantum dots (QDs) were introduced onto SiO2@Ag@SiO2. The dominant effect between plasmonic quenching and MEF was defined depending on the thickness of the silica shell between Ag and QDs. When the distance between Ag NPs to QDs was less than ~10 nm, SiO2@Ag@SiO2@QDs showed weaker fluorescence intensities than SiO2@QD (without metal) due to the quenching effect. On the other hand, when the distance between Ag NPs to QDs was from 10 nm to 14 nm, the fluorescence intensity of SiO2@Ag@SiO2@QD was stronger than SiO2@QDs due to MEF. The results provide background knowledge for controlling the thickness of silica shells in metal-containing nanocomposites and facilitate the development of potential applications utilizing the optimal plasmonic phenomenon. [ABSTRACT FROM AUTHOR]

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 (SiO2) nanoparticles (NPs) (SiO2@Au@Au NPs) as NIR SERS nanoprobes are synthesized using the seed-mediated growth method. SiO2@Au@Au NPs using six different sizes of Au NPs (SiO2@Au@Au50–SiO2@Au@Au500) were prepared by controlling the concentration of Au precursor in the growth step. The nanogaps between Au NPs on the SiO2 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. SiO2@Au@Au500 NPs with a 0.98-nm gap showed a high SERS enhancement factor of approximately 3.8 × 106 under 785-nm photoexcitation. SiO2@Au@Au500 nanoprobes showed detectable in vivo SERS signals at a concentration of 16 μg/mL in animal tissue specimen at a depth of 7 mm. SiO2@Au@Au500 NPs with 14 different Raman label compounds exhibited distinct SERS signals upon subcutaneous injection into nude mice. Conclusions: SiO2@Au@Au NPs showed high potential for in vivo applications as multiplex nanoprobes with high SERS sensitivity in the NIR region. [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman scattering (SERS) provides a unique non-destructive spectroscopic fingerprint for chemical detection. However, intrinsic differences in affinity of analyte molecules to metal surface hinder SERS as a universal quantitative detection tool for various analyte molecules simultaneously. This must be overcome while keeping close proximity of analyte molecules to the metal surface. Moreover, assembled metal nanoparticles (NPs) structures might be beneficial for sensitive and reliable detection of chemicals than single NP structures. For this purpose, here we introduce thin silica-coated and assembled Ag NPs (SiO2@Ag@SiO2 NPs) for simultaneous and quantitative detection of chemicals that have different intrinsic affinities to silver metal. These SiO2@Ag@SiO2 NPs could detect each SERS peak of aniline or 4-aminothiophenol (4-ATP) from the mixture with limits of detection (LOD) of 93 ppm and 54 ppb, respectively. E-field distribution based on interparticle distance was simulated using discrete dipole approximation (DDA) calculation to gain insight into enhanced scattering of these thin silica coated Ag NP assemblies. These NPs were successfully applied to detect aniline in river water and tap water. Results suggest that SiO2@Ag@SiO2 NP-based SERS detection systems can be used as a simple and universal detection tool for environment pollutants and food safety. [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman scattering ( SERS) has attracted considerable interest as a sensitive vibration-specific probe for bioanalytical and imaging applications. Among the various bioprobes available, Ag-embedded SERS tags have been rigorously developed for an extensive range of biodetection applications. In this review, we look at the additional functionality that SERS tags can offer via its magnetic properties, fluorescence, and an extension of the optical region into the near-infrared ( NIR) spectrum. Such functionality can be achieved by using Ag nanoparticles ( NPs) or Au/Ag hollow-shells ( HS) as a SERS signaling unit, with SiO2 nanospheres providing a back-bone unit. This back-bone can include a magnetic core (M- SERS dots), but also provides an outer shell that protects the optical unit and allows for easy conjugation of linkers that can include fluorescent organic dyes for an additional optical unit (F- SERS dots). In use, M- SERS dots allow for the separation of target cancer or cancer stem cells with an external magnetic field, while F- SERS dots can rapidly locate specific proteins within large areas of tissue and simultaneously analyze multiple targets based on their Raman signals. Moreover, NIR SERS dots can be detected with a high sensitivity within deep tissues, thus allowing them to be applied to in vivo multiplex detection. As none of these advanced functional SERS dots exhibit any sign of cytotoxicity for cell lines, they demonstrate a clear potential for more efficient, high-throughput screening of biological molecules using Raman technology. [ABSTRACT FROM AUTHOR]

For the effective application of surface-enhanced Raman scattering (SERS) nanoprobes for in vivo targeting, the tissue transparency of the probe signals should be as high as it can be in order to increase detection sensitivity and signal reproducibility. Here, near-infrared (NIR)-sensitive SERS nanoprobes (NIR SERS dots) are demonstrated for in vivo multiplex detection. The NIR SERS dots consist of plasmonic Au/Ag hollow-shell (HS) assemblies on the surface of silica nanospheres and simple aromatic Raman labels. The diameter of the HS interior is adjusted from 3 to 11 nm by varying the amount of Au3+ added, which results in a red-shift of the plasmonic extinction of the Au/Ag nanoparticles toward the NIR (700-900 nm). The red-shifted plasmonic extinction of NIR SERS dots causes enhanced SERS signals in the NIR optical window where endogenous tissue absorption coefficients are more than two orders of magnitude lower than those for ultraviolet and visible light. The signals from NIR SERS dots are detectable from 8-mm deep in animal tissues. Three kinds of NIR SERS dots, which are injected into live animal tissues, produce strong SERS signals from deep tissues without spectral overlap, demonstrating their potential for in vivo multiplex detection of specific target molecules. [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman scattering ( SERS) has attracted considerable interest as a sensitive vibration-specific probe for bioanalytical and imaging applications. Among the various bioprobes available, Ag-embedded SERS tags have been rigorously developed for an extensive range of biodetection applications. In this review, we look at the additional functionality that SERS tags can offer via its magnetic properties, fluorescence, and an extension of the optical region into the near-infrared ( NIR) spectrum. Such functionality can be achieved by using Ag nanoparticles ( NPs) or Au/Ag hollow-shells ( HS) as a SERS signaling unit, with SiO2 nanospheres providing a back-bone unit. This back-bone can include a magnetic core (M- SERS dots), but also provides an outer shell that protects the optical unit and allows for easy conjugation of linkers that can include fluorescent organic dyes for an additional optical unit (F- SERS dots). In use, M- SERS dots allow for the separation of target cancer or cancer stem cells with an external magnetic field, while F- SERS dots can rapidly locate specific proteins within large areas of tissue and simultaneously analyze multiple targets based on their Raman signals. Moreover, NIR SERS dots can be detected with a high sensitivity within deep tissues, thus allowing them to be applied to in vivo multiplex detection. As none of these advanced functional SERS dots exhibit any sign of cytotoxicity for cell lines, they demonstrate a clear potential for more efficient, high-throughput screening of biological molecules using Raman technology. [ABSTRACT FROM AUTHOR]