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Noble metals, especially gold, have been widely used in plasmon resonance applications. Although silver has a larger optical cross section and lower cost than gold, it has attracted much less attention because of its easy corrosion, thereby degrading plasmonic signals and limiting its applications. To circumvent this problem, we report the facile synthesis of superstable AgCu@graphene (ACG) nanoparticles (NPs). The growth of several layers of graphene onto the surface of AgCu alloy NPs effectively protects the Ag surface from contamination, even in the presence of hydrogen peroxide, hydrogen sulfide, and nitric acid. The ACG NPs have been utilized to enhance the unique Raman signals from the graphitic shell, making ACG an ideal candidate for cell labeling, rapid Raman imaging, and SERS detection. ACG is further functionalized with alkyne-polyethylene glycol, which has strong Raman vibrations in the Raman-silent region of the cell, leading to more accurate colocalization inside cells. In sum, this work provides a simple approach to fabricate corrosion-resistant, water-soluble, and graphene-protected AgCu NPs having a strong surface plasmon resonance effect suitable for sensing and imaging. [ABSTRACT FROM AUTHOR]

The combination of surface-enhanced Raman spectroscopy (SERS) technology with microfluidics makes it possible to diagnose genetic disease through label-free on-chip DNA detection. However, open problems including the integration of SERS substrate with microfluidic devices, controllable trapping and releasing of target molecules are still challenging. Here we demonstrate a facile laser scribing method to fabricate silver nanoparticles (AgNPs) and graphene oxide (GO) based biochips as a reusable SERS sensor for DNA detection. Programmable laser scribing of the AgNPs@GO composite film enables direct patterning of sensitive SERS channels that consist of graphene supported AgNPs by exfoliating the composites into hierarchical porous structures. Integrating the SERS-active patterns with a microfluidic chip forms a biochip for allowing SERS detection of DNA. The noncovalent interactions between DNA and graphene mediated controllable trapping and releasing of DNA sequences, enabling efficient on-chip SERS detection and the regeneration of the biochip. The simple, green and cost-effective fabrication of the SERS-active biochips reveals great potential for biomolecular sensing and genetic engineering applications. [ABSTRACT FROM AUTHOR]

Various interferences from measurement conditions and substrate inhomogeneity are well-known confounding factors for poor reproducibility, which is a challenge in surface-enhanced Raman scattering (SERS) quantification. To address these issues, novel substrates and versatile internal standards have been designed and the repeatability is improved to some degree. However, these internal standards are either complex or unstable enough to resist harsh environments such as acid and oxidation. Graphene-isolated-Au-nanocrystal (GLAN) has unique properties and been applied for cell multimodal imaging and chemotherapy but not for SERS quantification analysis yet. Herein, we chose GLANs to improve the accuracy of SERS analysis. GIAN integrates the SERS effect and internal standard into a simple nanoparticle and is proved to be an ideal platform for SERS analysis given its superior properties: (l) chemical stability, it remains stable in strong acid and oxidation, even mimic bioenvironment; (2) a simple core--shell structure, with a thin graphitic shell which is not only a protector that avoiding inner Au catalysis unnecessary reaction but also an internal standard to eliminate the interference during the Raman detections; (3) the big-IT structure can absorb target molecule thus achieve an enrichment effect and quench background fluorescence. Laser power, focus, and substrate fluctuations as well as coexist substance interferences were investigated and the accuracy was improved greatly with the introduction of 2D band internal standard in Raman silent region with less background. Moreover, GIAN was applied for crystal violet determination directly on fish muscle and scale, which was rapid and convenient without complex extraction process. All these results indicate GIAN is an optimum choice for SERS analysis in complex systems. [ABSTRACT FROM AUTHOR]

We present a design of multilayer core-shell nanostructures formed by introducing a dielectric gap shell layer between a silver core and a monolayer graphene shell for spectrally selective absorption enhancement in graphene based on an unconventional Fano effect. We demonstrate that this mechanism enables great flexibility in the choice of parameters of the proposed structures for the achievement of a relatively large and narrow-band absorption enhancement in graphene. Furthermore, we also demonstrate that such a spectrally selective absorption enhancement in graphene is highly tunable and can be optimized by controlling either the core or the shell parameters. These unique absorption properties may have applications in color-selective photodetectors and image sensors. [ABSTRACT FROM AUTHOR]

Solution-processed graphene quantum dots (GQDs) possess a moderate bandgap, which make them a promising candidate for optoelectronics devices. However, negative photoconductivity (NPC) and hysteresis that happen in the photoelectric conversion process could be harmful to performance of the GQDs-based devices. So far, their origins and relations have remained elusive. Here, we investigate experimentally the origins of the NPC and hysteresis in GQDs. By comparing the hysteresis and photoconductance of GQDs under different relative humidity conditions, we are able to demonstrate that NPC and hysteresis coexist in GQDs and both are attributed to the carrier trapping effect of surface adsorbed moisture. We also demonstrate that GQDs could exhibit positive photoconductivity with three-order-of-magnitude reduction of hysteresis after a drying process and a subsequent encapsulation. Considering the pervasive moisture adsorption, our results may pave the way for a commercialization of semiconducting graphene-based and diverse solution-based optoelectronic devices. [ABSTRACT FROM AUTHOR]