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The selection of an affordable method to fabricate plasmonic metasurfaces needs to guarantee complex control over both tunability and reproducibility of their spectral and morphological properties, making plasmonic metasurfaces suitable for integration into different sensing devices. Displacement Talbot lithography could be a valid solution thanks to the limited fabrication steps required, also providing the highly desired industrial scalability. Fabricated plasmonic metasurfaces are represented by a gold nanohole array on a glass substrate based on a triangular pattern. Scanning electron microscopy measurements have been recorded, showing the consistency of the surface features with the optimized design parameters. Reflectance and transmittance measurements have also been carried out to test the reliability and standardization of the metasurface’s optical response. Furthermore, these plasmonic metasurfaces have also been successfully tested for probing refractive index variations in a microfluidic system, paving the way for their use in sensitive, real-time, label-free, and multiplexing detection of bio-molecular events.

Plasmonic arrays are grating-like structures able to couple an incoming electromagnetic field into either localized or propagating surface plasmonic modes. A triangular array of elliptical holes in a gold layer were realized resorting to displacement Talbot lithography. Scanning electron microscopy was used to evaluate the geometrical features and finite time domain simulations were performed to verify the consistency of the design. The optical response was characterized by angle-resolved reflectance and transmittance measurements. The results demonstrate the good quality and uniformity of the array. Furthermore, the study on the dependence of the optical response on both the hexagonal lattice and the elliptical hole-defined symmetry properties was conducted allowing the distinction of their effects on both the localized and propagating plasmonic modes. The results indicate that the localized component of the plasmonic modes is mainly affected by the elliptical shape, while the propagating part is influenced by the hexagonal lattice symmetry.

Gold nanohole arrays are periodic metasurfaces that are gathering huge interest in biosensing applications. The bi-dimensional grating-like structure defines their plasmonic response, together with the corresponding mode of angular dispersion. These properties can be used to investigate the interaction processes with the fluorescence features of a properly chosen emitting molecule. By employing a custom gold nanohole array alongside a commercial organic dye, we conducted an accurate angle-resolved optical characterization resorting to fluorescence, reflectance, and transmittance spectra. The coupling between the plasmonic modes and the fluorescence features was then identified as a modification of the dye fluorescence signal in terms of both spectral redistribution and enhancement. By carefully analyzing the results, different measurement efficiencies can be identified, depending on the set-up configuration, to be properly engineered for sensitivity maximization in plasmon-enhanced fluorescence-based applications.

Gold nanohole arrays represent a class of bidimensional plasmonic metasurfaces that are suitable for realizing optical sensors. We propose a modeling approach based on a customized particle swarm optimization algorithm implemented in the commercial Ansys Lumerical FDTD software. Providing the relevant optical and morphological parameters, we obtain a set of optimized geometrical parameters tailored to the required features. Specifically, we deal with square and hexagonal arrays of air cylinders embedded in a gold layer deposited on a glass substrate engineered for surface plasmon resonance technique-based biosensors. Two structures have been defined and we plan to fabricate them to validate our design routine.

Plasmonic nanostructures represent a suitable platform for the detection of biomolecule interactions. Their surface functionalization can be performed through different strategies. Optimal thickness, homogeneity, and hydrophilicity of the functional layer can play a crucial role in defining the sensing capabilities required to perform bioassays. In this framework, a combination of tetraethylorthosilicate (TEOS) and a commercial polymer (MCP) was evaluated to improve these features. In our more recent studies, we focused on plasmon-enhanced fluorescence for the detection of a microbial-derived synthetic oligonucleotide. An effective improvement of the fluorescence signal was detected for the combined TEOS and MCP coating.

Nanostructured plasmonic surfaces have been the subject of many biosensing applications exploiting surface-enhanced fluorescence in the last few years. For this reason, we investigated the refractive index dependence of the coupling mechanism between the plasmonic modes and the fluorescence processes. The results show that the fluorescence emission spectral shape is controlled by the plasmonic field distribution, together with the enhancement of its signal. By altering the refractive index at the plasmonic active surface, the resonance conditions of the plasmonic modes change, resulting in a reshaping of fluorescence emission and a different spectral distribution of the largest enhancement regions.

The recent development and technological improvement in dealing with plasmonic metasurfaces has triggered a series of interesting applications related to sensing challenges. Fluorescence has been one of the most studied tools within such a context. With this in mind, we used some well characterized structures supporting plasmonic resonances to study their influence on the emission efficiency of a fluorophore. An extended optical analysis and a complementary investigation through finite-difference time-domain (FDTD) simulations have been combined to understand the coupling mechanism between the excitation of plasmonic modes and the fluorescence absorption and emission processes. The results provide evidence of the spectral shape dependence of fluorescence on the plasmonic field distribution together with a further relationship connected with the enhancement of its signal. It has made evident that the spectral region characterized by the largest relative enhancement closely corresponds to the strongest signatures of the plasmonic modes, as described by both the optical measurements and the FDTD findings.