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Imidacloprid is the most widely used insecticide in agriculture and its intensive use over the last 30 years has caused a global concern due to its potentially toxic effects on the ecosystem. Considering the recent scientific interest in novel simple methods for imidacloprid analysis, we propose a label-free sensitive and specific localised surface plasmon resonance system for the detection of the insecticide based on 2D nanostructured metasurfaces with highly performing plasmonic properties. The specificity of the sensor proposed was achieved by covalent bio-functionalization of the metasurface using a smart and easy one-step procedure mediated by carbon disulphide. The biosensor produced was tested using a set of imidacloprid standard solutions showing a competitive limit of detection, lower than 1 ng mL−1. Our novel nanosensing configuration represents a valid and reliable solution to realize low-cost portable POC tests as an alternative to the laborious and expensive methods traditionally used for insecticide detection. [ABSTRACT FROM AUTHOR]

In our bioassay protocol, the Ag@4MBA@DNA-biotin probes were synthesized by linking biotin-modified DNA and 4-mercaptobenzoic acid-covered Ag nanoparticles, and the Si@Ag@anti-digoxin/digoxin-DNA substrate was fabricated by immune linking of digoxin-DNA and anti-digoxin immobilized on a Ag-coated wafer. Then, the probes, miRNA-21 and the substrate were constructed into a “sandwich structure” to detect the variation in the SERS signals with respect to miRNA-21 concentrations. Next, streptavidin and extra probes were alternately introduced to implement the cascade amplification of the SERS signal to increase the detection sensitivity. The results show that the limit of detection (LOD) with cascade amplification is remarkably improved from 97.81 pM to 38.02 fM, which is three orders of magnitude higher than the original data without cascade amplification. Furthermore, the SERS-based cascade amplification mechanism was analyzed and is attributed to the “hot spots effect” of the noble metal nanostructure. The biotin-streptavidin (B–S) system was introduced into the SERS detection platform, and the novel SERS-based cascade amplification bioassay protocol has significant creativity for the detection of nucleic acids. [ABSTRACT FROM AUTHOR]

Well-shaped Ag@Au hexagonal nanorings (Ag@Au HNRs) were successfully synthesized with the assistance of Ag hexagonal nanoplates as structure-directing templates in a galvanic replacement route, and their optical characteristics were studied in detail. During the synthetic process, the morphology of the Ag@Au HNRs was found to be strongly depended on the dosage of HAuCl4 added into the template solution. Both the experimental and calculated absorption spectra showed that the red-shift of localized surface plasmon resonance (LSPR) peaks of the Ag@Au HNRs obeyed a modified Lorentz function with increasing dosage of HAuCl4 solution, which was also explained by the plasmon hybridization of the Ag@Au HNRs. Moreover, the surface-enhanced Raman scattering (SERS) characteristics of Ag@Au HNRs were investigated by using 4-mercaptobenzoic acid (4MBA) as a Raman reporter molecule. And the as-prepared Ag@Au HNRs exhibit excellent SERS performances with an enhancement factor ∼106, especially for the Ag@Au HNR prepared at 160 μl HAuCl4 solution due to its strongest plasmon electric-field enhancement. It reveals that the as-synthesized Ag@Au HNRs possess great potential for the application in ultrasensitive biosensors. [ABSTRACT FROM AUTHOR]

Novel Au@Ag core–shell nanocubes (NCs) were successfully prepared by the controlled epitaxial growth of Ag shells onto Au nanoellipsoids (NEs) in the presence of surfactants. The growth mechanism of the Au@Ag core–shell NCs was systematically investigated by analyzing their morphology, optical properties, and crystallography. The localized surface plasmon resonance (LSPR) characteristics and the electric field distribution of the Au@Ag core–shell NCs were studied using the finite element method (FEM) based on the plasmon hybridization theory. Compared with pure Ag NCs, the absorption spectrum of the Au@Ag core–shell NCs exhibits a red shift and a weak shoulder near 550 nm, and the notable enhancement of electric field occurs around the corners along the long-axis of the Au ellipsoidal core because of plasmonic resonant coupling. Surface-enhanced Raman scattering (SERS) of the Au@Ag core–shell NCs labeled with 4-mercaptobenzoic acid molecules reveals that the bimetallic core–shell NCs possess efficient SERS activity with an enhancement factor EF = 2.27 × 106, thus confirming the possibility of using the Au@Ag core–shell NCs as a stable probe for SERS-based biosensing applications. [ABSTRACT FROM AUTHOR]

A polymeric PEDOT:PSS film nanostructured with Photonic Quasi Crystals that opens the path towards more efficient white OLEDs is presented. For the first time three different quasi crystal families were fabricated (octagonal, dodecagonal and Thue-Morse) onto a conductive polymeric film combining high-resolution electron beam lithography (EBL) and plasma etching techniques to improve light extraction and to control spectral tunability. The efficiency gain obtained in light extraction holds great promise for the use of quasi crystals as functional components in polymeric based White Organic Light Emitting Diode (WOLED) devices. [ABSTRACT FROM AUTHOR]

Hollow sea-urchin gold nanoparticles (HSU-GNPs) were successfully prepared through a novel one-step galvanic replacement strategy, and their corresponding optical properties was studied in detail. During the synthesis process, the sizes of the interior hollows of the HSU-GNPs could be changed by adjusting the amount of silver nitrate added into hydrogen tetrachloroaurate trihydrate solution. The absorption spectra of the HSU-GNPs showed that the localized surface plasmon resonance (LSPR) peaks were red-shifted with increasing size of the interior hollows in the HSU-GNPs. When the added amount of silver nitrate was up to 6 μl, the LSPR peak of the synthesized HSU-GNP reached 726 nm as a maximum red-shift. Furthermore, the absorption spectra of the HSU-GNPs with different morphologies were theoretically simulated by the finite element method, which was consistent with the experimental results and explained the origin of the red-shift of the LSPR peaks. In addition, the surface-enhanced Raman scattering (SERS) of the sea urchin gold nanoparticles were also investigated using 4-mercaptobenzoic acid as a Raman reporter molecule. Both the experimental and calculated results showed that the HSU-GNPs had stronger SERS enhancement than the solid sea-urchin gold nanoparticles. In particular, the HSU-GNPs prepared by adding 6 μl silver nitrate exhibited a maximum SERS enhancement factor, EF = 1.1 × 109, due to the LSPR peak at 726 nm which is near to the excitation wavelength, 785 nm. This feature is significant for designing a biosensor with a super-high sensitivity based on the morphology of the HSU-GNPs. [ABSTRACT FROM AUTHOR]