arXiv subjects

Souhir Boujday

Publications and source records attributed to Souhir Boujday.

4 recordsLinked to original sources

arXiv2026

Synthesis of hybrid gold-protein nanobioconjugates with strongly enhanced circular dichroism

Controlling chiral light-matter interactions with nanophotonics is a powerful strategy for amplifying molecular circular dichroism (CD) beyond its natural limits. Here, we present a plasmonic platform that uses superchiral near fields to amplify the optical activity of biological chromophores. Gold nanoparticles (3.6 nm in diameter) are electrostatically coupled with photosynthetic proteins which results in stable hybrid nanobioconjugates in aqueous solution. The Q-band absorption spectrum of the proteins overlaps with the localized surface plasmon resonance of the gold particles. In the visible region, a combination of numerical simulations and normalized CD measurements reveal an enhancement factor of 3 compared to free proteins. This observation reveals three effects. First, there is a local increase in electromagnetic chirality density in the protein environment. Second, there is an increase in the absorption of the proteins. Third, there is plasmon-induced circular dichroism. Our results quantitatively demonstrate that near-field super-chirality directly modulates biomolecular optical activity. These findings open new avenues for chiroptical nanodevices, biosensing platforms, and light-driven asymmetric photochemistry.

physics.optics↗

arXiv2025

Probing Peptide Adsorption Kinetics and Regioselectivity via Multipolar Plasmonic Modes of Gold Resonators

Efficient peptide adsorption on metasurfaces is essential for advanced biosensing applications. In this study, we demonstrate how ellipsometric measurements coupled with numerical simulations allow for real-time tracking of temporin-SHa peptide adsorption on gold metasurfaces. By characterizing spectral shifts at 660 nm, 920 nm, and 1000 nm, we reveal a rapid saturation of surface coverage after 3.5 hours, with a significant preferential adsorption at the resonator ends. Our approach provides a novel methodology for monitoring peptide binding, which could be applied to a wide range of biosensor designs.

physics.optics↗

arXiv2023

True Circular Dichroism in Optically Active Achiral Metasurfaces and Its Relation to Chiral Near-Fields

Optically active achiral metasurfaces offer a promising way to detect chiral molecules based on chiroptic methods. The combination of plasmonic enhanced circular dichroism and reversible optical activity would boost the sensitivity and provide enantiomerselective surfaces while using a single sensing site. In this work, we use metasurfaces containing arrays of U-shaped resonators as a benchmark for analyzing the optical activity of achiral materials. Although the peculiar optical activity of these metasurfaces has 1 been quite well described, we present here an experimental and numerical quantitative determination of the different contributions to the measured optical activity. In particular, it is shown that linear birefringence and retardance contribute, but only marginally, to the apparent circular dichroism of the metasurface associated with the excitation of magnetoelectric modes. We then numerically demonstrate the peculiar near-field properties of the magneto-electric modes and explain how these properties could be reflected in the far-field polarimetric properties in the presence of chiral molecules. This work provides alternatives for the detection scheme of chiral molecules using plasmonic resonators.

physics.app-ph↗

arXiv2019

The Prevailing Role of Hotspots in Plasmon-Enhanced Sum-Frequency Generation Spectroscopy

The plasmonic amplification of non-linear vibrational sum frequency spectroscopy (SFG) at the surfaces of gold nanoparticles is systematically investigated by tuning the incident visible wavelength. The SFG spectra of dodecanethiol-coated gold nanoparticles chemically deposited on silicon are recorded for twenty visible wavelengths. The vibrational intensities of thiol methyl stretches extracted from the experimental measurements vary with the visible color of the SFG process and show amplification by coupling to plasmonics. Since the enhancement is maximal in the orange-red region rather than in the green, as expected from the dipolar model for surface plasmon resonances, it is attributed mostly to hotspots created in particle multimers, in spite of their low surface densities.

physics.optics↗