Graphene oxide-gold nanoparticle (AuNPs@GO) hybrids were fabricated in water dispersions of graphene oxide (GO) and Au precursor completely free of stabilizing agents by UV-light irradiation. Gold nanoparticle (AuNP) nucleation, growth, and stabilization mechanisms at the surface of GO are discussed on the basis of UV-Vis, Raman, IR, and X-Ray photo-spectroscopy studies. The analyses of AuNPs@GO hybrids by transmission electron microscopy (TEM), thermogravimetric (TGA) and electrochemical tests show that they exhibit outstanding chemical, thermal and electrochemical stabilities. Thus, AuNPs@GO biosensing platforms were fabricated for surface enhanced Raman spectroscopy (SERS) detection of crystal violet (CV), a SERS standard molecule, and in a different set of experiments, for flavin adenine dinucleotide (FAD), a flavoprotein coenzyme that plays an important role in many oxidoreductase and reversible redox conversions in biochemical reactions. AuNPs@GO hybrids synthesized by using UV light irradiation show exceptional stability and high intensification of the Raman signals showing that they have high potential for use as biomedical probes for the detection, monitoring, and diagnosis of medical diseases.

The modification of transition-metal dichalcogenides (TMDs), incorporating nitrogen (N) doping and silver nanoparticles (Ag NPs ) decoration on the skeleton of exfoliated MoS 2 and WS 2 , was accomplished. The preparation of N-doped and Ag NPs -decorated TMDs involved a one-pot treatment procedure in a vacuum-sputtering chamber under N plasma conditions and in the presence of a silver (Ag) cathode as the source. Two different deposition times, 5 and 10 s, respectively, were applied to obtain N-doped with Ag NPs -decorated MoS 2 and WS 2 hybrids, abbreviated as N5-MoS 2 /Ag NPs , N10-MoS 2 /Ag NPs , N5-WS 2 /Ag NPs , and N10-WS 2 /Ag NPs , respectively, for each functionalization time. The successful incorporation of N as the dopant within the lattice of exfoliated MoS 2 and WS 2 as well as the deposition of Ag NPs on their surface, yielding N-MoS 2 /Ag NPs and N-WS 2 /Ag NPs , was manifested through extensive X-ray photoelectron spectroscopy measurements. The observation of peaks at ∼398 eV derived from covalently bonded N and the evolution of a doublet of peaks at ∼370 eV guaranteed the presence of Ag NPs in the modified TMDs. Also, the morphologies of N-MoS 2 /Ag NPs and N-WS 2 /Ag NPs were examined by transmission electron microscopy, which proved that Ag deposition resulted in nanoparticle growth rather than the creation of a continuous metal film on the TMD sheets. Next, the newly developed hybrid materials were proven to be efficient surface-enhanced Raman scattering (SERS) platforms by achieving the detection of Rhodamine B (RhB). Markedly, N10-MoS 2 /Ag NPs showed the highest sensitivity for detecting RhB at concentrations as low as 10 −9 M. Charge-transfer interactions between RhB and the modified TMDs, together with the polarized character of the system causing dipole−dipole coupling interactions, were determined as the main mechanisms to induce the Raman scattering enhancement. Finally, polycyclic aromatic hydrocarbons such as pyrene, anthracene, and 2,3-dihydroxynaphthalene, coordinated via π−S interactions with N-MoS 2 /Ag NPs , were screened with high sensitivity and reproducibility. These findings highlight the excellent functionality of the newly developed N-MoS 2 /Ag NPs and N-WS 2 /Ag NPs hybrid materials as SERS substrates for sensing widespread organic and environmental pollutants as well as carcinogen and mutagen species.

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In the search for the integration of carbon nanostructures in composite and functional materials, covalent organic reactions are successfully performed. This approach resulted in the construction of tailored chemical interfaces facilitating incorporation of nanocarbons. By a combination of different characterization techniques, such as high-resolution X-ray photo-spectroscopy, thermogravimetric analysis, Raman spectroscopy, UV-vis-nIR, and fluorescence spectroscopies, it is possible to identify and quantify the functional moieties covalently attached to the carbon frame. However, the determination of the structural conformation of functionalized nanostructures remains a difficult task. In this work, we present a straightforward methodology to visualize by transmission electron microscopy the functional moieties covalently attached to the carbon network in carbon nanotubes and graphene. The identification of the functionalities occurs in colloidal dispersions by using gold nanoparticles (AuNPs) as discriminating markers by molecular recognition or by the direct growth of AuNPs on the oxygenated moieties. This methodology, in combination with other characterization analysis, is expected to improve the design of hierarchical interfaces by the spatial localization of the functionalities responsible for colloidal stabilization in solvents with different polarities, different from their homogeneous incorporation into different matrices.