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- Analysis of metallic nanoparticles embedded in thin film semiconductors for optoelectronic applicationsPublication . Fantoni, Alessandro; Fernandes, Miguel; Vygranenko, Yuri; Louro, Paula; Vieira, Manuela; Silva, R. P. O.; Teixeira, D.; Da Costa Ribeiro, Ana Paula; Prazeres, Duarte; Alegria, ElisabeteThis paper reports about a study of the local plasmonic resonance (LSPR) produced by metal nanoparticles embedded in a dielectric or semiconductor matrix. It is presented an analysis of the LSPR for different nanoparticle metals, shapes, and embedding media composition. Metals of interest for nanoparticle composition are Aluminum and Gold. Shapes of interest are nanospheres and nanotriangles. We study in this work the optical properties of metal nanoparticles diluted in water or embedded in amorphous silicon, ITO and ZnO as a function of size, aspect-ratio and metal type. Following the analysis based on the exact solution of the Mie theory and DDSCAT numerical simulations, it is presented a comparison with experimental measurements realized with arrays of metal nanospheres. Simulations are also compared with the LSPR produced by gold nanotriangles (Au NTs) that were chemically produced and characterized by microscope and optical measurements.
- Characterization of plasmonic effects in AuNP+rGO composite as a sensing layer for a low-cost lab-on-chip biosensorPublication . Fantoni, Alessandro; Stojkovic, Vladan; Fernandes, Miguel; Louro, Paula; Vieira, Manuela; Alegria, Elisabete; Da Costa Ribeiro, Ana Paula; Carvalho, Ana; Almeida, M. GabrielaThis work deals with the production of a low-cost disposable biosensor for point of care applications. The proposed sensor is a plasmonic structure based on the Localized Surface Plasmon Resonance (LSPR) interaction of metal nanoparticles (MNPs), embedded into a matrix of reduced Graphene Oxide (rGO). After proper functionalization with selective antibodies (Ab), the efficiency of light extinction is controlled by slight changes of the refractive coefficient induced by the concentration of biomarkers trapped by the antibodies on the sensor surface. This work reports a study about the applicability of rGO as a support for gold nanoparticles (AuNPs) for preparing the functionalized LSPR sensing layer. AuNPs are prepared with an economic and eco-friendly method using phytochemicals present in tea extract at room temperature, while a modified Hummer’s method is used to synthesize rGO. The resulting AuNPs-rGO composites are studied in terms of UV-VIS spectroscopy spectral light transmission and plasmonic resonance. The overall analysis is supported by simulation results, obtained by Mie analysis, about the LSPR effect in AuNPs-rGO and its dependence on the biomarker concentration.
- Optical properties of metal nanoparticles embedded in amorphous silicon analysed using discrete dipole approximationPublication . Fantoni, Alessandro; Fernandes, Miguel; Vygranenko, Yuri; Vieira, Manuela; Oliveira-Silva, Rui; Prazeres, Duarte; Da Costa Ribeiro, Ana Paula; Alegria, ElisabeteLocalized surface plasmons (LSP) can be excited in metal nanoparticles (NP) by UV, visible or NIR light and are described as coherent oscillation of conduction electrons. Taking advantage of the tunable optical properties of NPs, we propose the realization of a plasmonic structure, based on the LSP interaction of NP with an embedding matrix of amorphous silicon. This study is directed to define the characteristics of NP and substrate necessary to the development of a LSP proteomics sensor that, once provided immobilized antibodies on its surface, will screen the concentration of selected antigens through the determination of LSPR spectra and peaks of light absorption. Metals of interest for NP composition are: Aluminium and Gold. Recent advances in nanoparticle production techniques allow almost full control over shapes and size, permitting full control over their optical and plasmonic properties and, above all, over their responsive spectra. Analytical solution is only possible for simple NP geometries, therefore our analysis, is realized recurring to computer simulation using the Discrete Dipole Approximation method (DDA). In this work we use the free software DDSCAT to study the optical properties of metal nanoparticles embedded in an amorphous silicon matrix, as a function of size, shape, aspect-ratio and metal type. Experimental measurements realized with arrays of metal nanoparticles are compared with the simulations.
- A simulation study of surface plasmons in metallic nanoparticles: dependence on the properties of an embedding a-Si:H MatrixPublication . Fantoni, Alessandro; Fernandes, Miguel; Vygranenko, Yuri; Louro, Paula; Vieira, Manuela; Alegria, Elisabete; Da Costa Ribeiro, Ana Paula; Teixeira, DanielaThe development and realization of a plasmonic structure based on the LSP interaction of metal nanoparticles with an embedding matrix of amorphous silicon is proposed. As a planned application, this structure will need to be usable as the basis for a sensor device applied in biomedical applications, after proper functionalization with selective antibodies. The final sensor structure needs to be low-cost, compact, and disposable. The study reported in this paper aims to analyze varied materials for nanoparticles embedded in an amorphous silico matrix. Metals of interest for nanoparticles composition are aluminum and gold. As a comparison term, a non-plasmonic material like alumina, resulting from oxidation of Al nanoparticles, is also considered. As a preliminary approach to this device, we study in this work the optical properties of spherical metal nanoparticles embedded in an amorphous silicon matrix, as a function of size and metal type. Following an analysis based on the exact solution of the Mie theory, experimental measurements realized with arrays of metal nanoparticles are compared with the simulations.
- Characterization of plasmonic effects in AuNP+rGO composite as a sensing layer for a low-cost lab-on-chip biosensorPublication . Fantoni, Alessandro; Stojkovic, Vladan; Fernandes, Miguel; Louro, Paula; Vieira, Manuela; Alegria, Elisabete; Da Costa Ribeiro, Ana Paula; Carvalho, Ana; Almeida, M. GabrielaThis work deals with the production of a low-cost disposable biosensor for point of care applications. The proposed sensor is a plasmonic structure based on the Localized Surface Plasmon Resonance (LSPR) interaction of metal nanoparticles (MNPs), embedded into a matrix of reduced Graphene Oxide (rGO). After proper functionalization with selective antibodies (Ab), the efficiency of light extinction is controlled by slight changes of the refractive coefficient induced by the concentration of biomarkers trapped by the antibodies on the sensor surface. This work reports a study about the applicability of rGO as a support for gold nanoparticles (AuNPs) for preparing the functionalized LSPR sensing layer. AuNPs are prepared with an economic and eco-friendly method using phytochemicals present in tea extract at room temperature, while a modified Hummer’s method is used to synthesize rGO. The resulting AuNPs-rGO composites are studied in terms of UV-VIS spectroscopy spectral light transmission and plasmonic resonance. The overall analysis is supported by simulation results, obtained by Mie analysis, about the LSPR effect in AuNPs-rGO and its dependence on the biomarker concentration.
- Plasmonic properties of gold nanospheres coupled to reduced graphene oxide for biosensing applicationsPublication . Fantoni, Alessandro; Stojkovic, Vladan; Fernandes, Miguel; Vieira, Manuela; Alegria, Elisabete; Da Costa Ribeiro, Ana PaulaGraphene-based materials have been extensively explored in recent years as valuable candidates as the key material for novel structures in the field, among many other applications, of sensing devices. Reduced Graphene Oxide (rGO) is a type of chemically derived graphene, with equivalent optical properties but easier to be synthetized. This work reports a study about the applicability of rGO as a support for gold nanoparticles (AuNPs). The resulting AuNPs-rGO composites are studied in terms of spectral light transmission and plasmonic resonance as a possible sensing element for a photonic protein sensor device.