Gabriele Zacco

Light absorption enhancement in heterostructure organic solar cells through the integration of 1-D plasmonic gratings.

The integration of a plasmonic lamellar grating in a heterostructure organic solar cell as a light trapping mechanism is investigated with numerical Finite Elements simulations. A global optimization of all the geometric parameters has been performed. The obtained wide-band enhancement in optical absorption is correlated with both the propagating and the localized plasmonic modes of the structure, which have been identified and characterized in detail.

Label-Free Efficient and Accurate Detection of Cystic Fibrosis Causing Mutations Using an Azimuthally Rotated GC-SPR Platform

Plasmonic nanosensors are candidates for the development of new sensors with low detection limits, high sensitivity, and specificity for target detection: these characteristics are of critical importance in the screening of mutations responsible for inherited diseases. In this work, we focused our study on the detection of some of the most frequent mutations responsible for cystic fibrosis (CF) among the Italian population. For the detection of the CF mutations we adopted a recently developed and highly sensitive Grating Coupled-Surface Plasmon Resonance (GC-SPR) enhanced spectroscopy method for label-free molecular identification exploiting a conical illumination configuration. Gold sinusoidal gratings functionalized with heterobifunctional PEG were used as sensing surfaces, and the specific biodetection was achieved through the coupling with DNA hairpin probes designed for single nucleotide discrimination. Such substrates were used to test unlabeled PCR amplified homozygous wild type (wt) and heterozygous samples, deriving from clinical samples, for the screened mutations. Hybridization conditions were optimized to obtain the maximum discrimination ratio (DR) between the homozygous wild type and the heterozygous samples. SPR signals obtained from hybridizing wild type and heterozygous samples show DRs able to identify univocally the correct genotypes, as confirmed by fluorescence microarray experiments run in parallel. Furthermore, SPR genotyping was not impaired in samples containing unrelated DNA, allowing the platform to be used for the concomitant discrimination of several alleles also scalable for a high throughput screening setting.

Coupled SPP Modes on 1D Plasmonic Gratings in Conical Mounting

Plasmonic nanostructures exhibit a variety of surface plasmon polariton (SPP) modes, with different characteristic properties. While a single metal dielectric interface supports a single-interface SPP mode, a thin metal film can support extended long range SPPs and strongly confined short range SPPs. When the coupling between the incident light and the SPP is provided through a diffraction grating, it is possible to azimuthally rotate the grating with respect to the scattering plane, introducing the possibility to propagate the SPP along an arbitrary direction. We present a theoretical and experimental analysis of the coupling conditions for long range and short range SPPs under this configuration. We also investigate the propagation length of the modes depending on the propagation direction with respect to the grating grooves, showing in particular that the long range SPP propagation length can be sensibly enhanced with respect to the null-azimuth case.

Plasmonic Sensors for Aromatic Hydrocarbon Detection

The development of innovative materials for sensitive and selective gas sensing is a very relevant field for the current nanotechnology research. A strong effort is dedicated to the fabrication of low-cost and efficient nanoscale devices capable of a fast detection. Resistive electrical devices are the most adopted solutions for in-situ and real-time detection, but their main drawbacks are the low selectivity, response drift, electromagnetic noise dependence and need of contact measurements. Optical gas sensors allow to overcome such limits, and could moreover exhibit thermal and mechanical stability, operate at room temperature, and be integrated on-chip. Within this framework, plasmon-based optical devices are knowing an increasing development and diffusion. Herein plasmonic sensors for aromatic hydrocarbon detection are presented. These systems are based on aryl-bridged polysilsesquioxanes (aryl-PSQs), obtained either \(\textcircled{1}\) coupling such hybrid films with Au nanoparticles (NPs), aiming to the excitation of localized surface plasmon resonances (LSPRs), or \(\textcircled{2}\) depositing them onto metallic waveguiding layers, to form gratings supporting the propagation of surface plasmon polaritons (SPPs). Aryl-PSQs are sol-gel materials characterized by a native controlled porosity and other functionalities (Loy and Shea, Chem Rev 95:1431–1442, 1995; Dabrowski et al., Appl Surf Sci 253:5747–5751, 2007; Brigo et al., Nanotechnology 23:325302, 2012). Temperature programmed desorption investigations of xylene on phenyl-bridged (ph-PSQ) and diphenyl-bridged (diph-PSQ) PSQ films indicate a specific π −π interaction between the organic component of the films and xylene molecules: the interaction energy is quantified in 38 ± 14 kJ/mol and 115 ± 13 kJ/mol, respectively (Brigo et al., J Mater Chem C 1:4252, 2013). For type \(\textcircled{1}\) sensors, a thin film of aryl-PSQ was deposited on a submonolayer of Au NPs coating a fused silica substrate. These sensors were tested monitoring the variation of the LSPRs under cycles of exposure to N2 and to 30 ppm xylene in N2.

Novel compact architecture for high-resolution sensing with plasmonic gratings in conical mounting

A novel compact architecture implementing grating-coupled surface plasmon resonance (GCSPR) based on polarization modulation in conical mounting is presented. In this system a plasmonic grating is azimuthally rotated in order to support the excitation of high-sensitivity surface plasmon polaritons (SPPs). At SPP resonance, a scan of the incident polarization is performed before and after the binding event and the phase term of the output trend is exploited as sensing parameter. The mechanical complexity of the SPR system is significantly reduced and a resolution down to 10-7 refractive index units is assured. In this work a numerical study of the polarization-based grating-coupled SPR technique is performed and analyzed with Chandezon’s method. Therefore an experimental test on an assembled prototype is presented and applied to the detection of binding events on the grating surface (avidin/biotin reaction, DNA/PNA probes).

Role of Resonances of Digital Plasmonic Gratings in Absorption Profile Remodulation in Silicon Solar Cells

Optical simulations of 1-D digital plasmonic grating show that SPPs and cavity-mode resonances can be effectively exploited to enhance NIR-light absorption in shallower regions of a Silicon substrate.