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The Ag-Au compound nanostructure films with controllable patterns of Ag nanoparticle (NP) aggregates were fabricated. A strategy of two-step synthesis was employed toward the target products. Firstly, the precursor Au NP (17nm) films were synthesized as templates. Secondly, the Ag NPs (45nm) were deposited on the precursor films. Three types of Ag NP aggregates were obtained including discrete Ag NPs (discrete type), necklace-like Ag NP aggregates (necklace type), and huddle-like Ag NP aggregates (huddle type). The surface-enhanced Raman scattering (SERS) property was studied on these nanostructures by using the probing molecule of rhodamine 6G under the excitation laser of 514.5nm. Interestingly, the different types of samples showed different enhancement abilities. A statistical method was employed to assess the enhancement. The relative enhancement factor for each Ag NP was estimated quantitatively under the ratio of 1 : 25 : 18 for the discrete-type, necklace-type, and huddle-type samples at the given concentration of 10_8 mol/l. This research shows that the enhancement ability of each Ag NP is dependent on the aggregate morphology. Moreover, the different enhancement abilities displayed different limit detection concentrations up to 10-8, 10-11, and 10-9 mol/l, separately. The understanding of the relationship between the defined nanostructures and the SERS enhancement is very meaningful for the design of new SERS substrates with better performance. [ABSTRACT FROM AUTHOR]

Highlights: [•] The layer-by-layer self-assembly technique was employed for the deposition of Ag nanoparticle films on glass substrates. [•] A thermal-induced reconstruction of the polyelectrolyte-linked nanoparticle films was presented. [•] The SERS property was highly improved after the reconstruction. [Copyright &y& Elsevier]

Highlights: [•] Silver nanotriangles array with long ranged periodicity was fabricated on the surface of glass wafer. [•] High enhancement of the fluorescent intensity of the target antibodies was obtained by the silver nanotriangles array. [•] High sensitivity and good reproducibility for antibodies detection was obtained by the 2D silver nanotriangles array. [ABSTRACT FROM AUTHOR]

With the explosive application of methyl salicylate (MS) molecules in food and cosmetics, the further detection of MS molecules becomes particularly important. Here we investigated the detection of MS molecules based on surface-enhanced Raman scattering (SERS) in a novel molecule/assistant/metal system constructed with MS, 4,4′-(hexafluoroisopropylidene) bis (benzoic acid) and Ag nanoparticles (AgNPs). The minimum detection concentration is 10 −4  M. To explore the function of assisted reagent, we also referred another system without assistant molecules. The result demonstrates that SERS signals were not acquired, which proves that the assistant molecules are critical for the capture of MS molecules. Two possible mechanisms of MS/assistant/AgNPs system were speculated through two patterns of hydrogen bonds. The linker molecules acted as the role of the bridge between metallic substrates and target molecules through the molecular recognition. This strategy is very beneficial to the expanding of MS detection techniques and other hydrogen bond based coupling detections with SERS. [ABSTRACT FROM AUTHOR]

A new type of surface-enhanced Raman scattering (SERS) substrate was fabricated through the layer-by-layer self-assembly of silver nanoparticles (AgNPs, av. 45 nm in diameter) and porous gold nanoclusters/nanoparticles (AuNPs, av. 143 nm in diameter). The development of the porosity of the AuNPs was investigated, and successful SERS applications of the porous AuNPs were also examined. As compared with AgNP films, the enhancement factor of Ag-Au compound substrates is increased 6 times at the concentration of 10 −6 M. This additional enhancement contributes to the trace-amount-detection of target molecules enormously. The contribution is generated through the increase of the usable surface area arising from the nanoscale pores distributed three-dimensionally in the porous AuNPs, which enrich the adsorption sites and hot spots for the adsorption of probe molecules, making the developed nanofilms highly sensitive SERS substrates. The substrates were used for the detection of a physiological metabolite of urea molecules. The results reached to a very low concentration of 1 mM and exhibited good quantitative character over the physiological concentration range (1 ∼ 20 mM) under mimicking biophysical conditions. These results show that the prepared substrate has great potential in the ultrasensitive SERS-based detection and in SERS-based biosensors. [ABSTRACT FROM AUTHOR]

A method for the investigation of photocatalytic degradation of organic molecules adsorbed on the surface of a compound nanostructure, silver nanoparticle (Ag NP) modified titania nanotubes (TiO 2 NTs), namely Ag/TiO 2 NTs, was proposed. The method was applied to the photocatalytic degradation of rhodamine 6G (R6G) dye molecules in order to determine its effectiveness. The surface-enhanced Raman scattering (SERS) technique was employed to monitor the photodegradation processes on these bifunctional nanostructures. The photocatalytic characteristic was attributed to the TiO 2 NTs; however, the SERS activity was caused by the Ag NPs. The Ag/TiO 2 NTs were able to detect R6G molecular probes with concentration down to 10 −8 M. The substrates could not only degrade the adsorbates, but also discard them off under ultraviolet irradiation owing to the high photocatalytic activity of TiO 2 . Thus, the substrates were able to self-clean and be reused for a new SERS detection cycle. The photodegradation and SERS results revealed that Ag/TiO 2 NTs acted as promising candidates for photocatalytic activity and SERS substrates; and exhibited high recyclability in the detection of organic molecules. The optimized SERS-active substrates were then employed to study the photodegradation of R6G. The photodegradation kinetics analysis was assessed by selecting the strongest SERS peaks which indicated that the kinetics of the photodegradation of R6G followed the pseudo-first order reaction. Finally, the results presented herein demonstrated that the fabricated Ag/TiO 2 NTs nanostructures were remarkably suitable as photocatalytically active SERS substrates. Further, the substrates could be effectively utilized for highly sensitive in situ monitoring of the surface photodegradation processes of organic molecules and could be recycled in a more environmentally sustainable manner. [ABSTRACT FROM AUTHOR]

Highlights: [•] CdTe QDs modified PS spheres with Ag NP caps were obtained. [•] A site-selective deposition effect was introduced. [•] Both fluorescence and SERS properties were investigated. [Copyright &y& Elsevier]