An inverted pyramidal metasurface was designed, fabricated, and studied at the nanoscale level for the development of a label-free pathogen detection on a chip platform that merges nanotechnology and surface-enhanced Raman scattering (SERS). Based on the integration and synergy of these ingredients, a virus immunoassay was proposed as a relevant proof of concept for very sensitive detection of hepatitis A virus, for the first time to our best knowledge, in a very small volume (2 μL), without complex signal amplification, allowing to detect a minimal virus concentration of 13 pg/mL. The proposed work aims to develop a high-flux and high-accuracy surface-enhanced Raman spectroscopy (SERS) nanobiosensor for the detection of pathogens to provide an effective method for early and easy water monitoring, which can be fast and convenient.

frequencies of light depending on the nanoparticle size, shape, material, and local dielectric environment. [1] This localized surface plasmon resonance (LSPR) effect can confine light in subwavelength volumes, [2] resulting in the generation of an enhanced electric field. However, these resonances are typically short lived, due to intrinsic high radiative optical losses that limit the associated quality factors (<10). [3] Nonetheless, arranging plasmonic nanoparticles into ordered arrays emerged as a convenient strategy to overcome this limitation and to boost the quality factors of the system. In this configuration the optical losses associated with LSPRs can be compensated under Bragg conditions by hybridization with the scattered waves in the plane of the array close to the position of the Rayleigh-Wood anomalies. [3] This compensation generates lattice plasmon resonances, and offers an additional possibility for tuning the optical properties, depending on the angle of illumination and the geometrical parameters of the array. [3] Due to their narrow bandwidth (<2 nm) and long lifetimes, [3][4][5] lattice plasmon resonances already impact the enhancement and manipulation of light-matter interactions, [6][7][8] sensing, [9][10][11][12] displays, [13] information storage [14] and anti-reflective materials. [15] The development of a simple, scalable, and rapid technique that combines the benefits of top-down and bottom-up methods Precise arrangements of plasmonic nanoparticles on substrates are important for designing optoelectronics, sensors and metamaterials with rational electronic, optical and magnetic properties. Bottom-up synthesis offers unmatched control over morphology and optical response of individual plasmonic building blocks. Usually, the incorporation of nanoparticles made by bottom-up wet chemistry starts from batch synthesis of colloids, which requires time-consuming and hard-to-scale steps like ligand exchange and self-assembly. Herein, an unconventional bottom-up wet-chemical synthetic approach for producing gold nanoparticle ordered arrays is developed. Water-processable hydroxypropyl cellulose stencils facilitate the patterning of a reductant chemical ink on which nanoparticle growth selectively occurs. Arrays exhibiting lattice plasmon resonances in the visible region and near infrared (quality factors of >20) are produced following a rapid synthetic step (<10 min), all without cleanroom fabrication, specialized equipment, or selfassembly, constituting a major step forward in establishing in situ growth approaches. Further, the technical capabilities of this method through modulation of the particle size, shape, and array spacings directly on the substrate are demonstrated. Ultimately, establishing a fundamental understanding of in situ growth has the potential to inform the fabrication of plasmonic materials; opening the door for in situ growth fabrication of waveguides, lasing platforms, and plasmonic sensors.

Plasmonic gold nanoparticles have been used increasingly in solid-state systems because of their applicability in fabricating novel sensors, heterogeneous catalysts, metamaterials, and thermoplasmonic substrates. While bottom-up colloidal syntheses take advantage of the chemical environment to control size, shape, composition, surface chemistry, and crystallography of the nanostructures precisely, it can be challenging to assemble nanoparticles rationally from suspension onto solid supports or within devices. In this Review, we discuss a powerful recent synthetic methodology, bottom-up in situ substrate growth, which circumvents time-consuming batch presynthesis, ligand exchange, and selfassembly steps by applying wet-chemical synthesis to form morphologically controlled nanostructures on supporting materials. First, we briefly introduce the properties of plasmonic nanostructures. Then we comprehensively summarize recent work that adds to the synthetic understanding of in situ geometrical and spatial control (patterning). Next, we briefly discuss applications of plasmonic hybrid materials prepared by in situ growth. Overall, despite the vast potential advantages of in situ growth, the mechanistic understanding of these methodologies remains far from established, providing opportunities and challenges for future research.

Templated self-assembly has emerged as one of the most versatile approaches for the fabrication of plasmonic ordered arrays composed of colloidal nanoparticle clusters, representing a valid alternative to top-down lithography...