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<p>In this paper, we propose a novel design and analysis of nanobiosensors utilizing plasmon-exciton (plexciton) coupling in geometrically optimized core–shell nanoshells. They consist of a core of plasmonic nanoparticles coated with molecules as a shell with various geometrical configurations such as elliptical, spherical, nanorod, rounded cone-like, cone-like, and truncated cone-like nanoshells for advanced biosensing applications, particularly focusing on cancer detection. Through a semiclassical modeling approach combining classical electromagnetic field treatment with quantum emitter responses via the optical Bloch equation, we employ three-dimensional finite difference time domain (3D-FDTD) simulations of Maxwell-Bloch equations to investigate the optical properties and optical field distributions of these nanobiosensor designs. The effects of key parameters are investigated, including the core and shell geometrical parameters, quantum emitter parameters, and the refractive index of the surrounding media. These hybrid nanosensors are engineered to detect minute refractive index changes associated with cancer biomarkers, offering potential for early-stage diagnosis of five cancer types: skin, breast, adrenal gland, cervical, and blood cancer with particular emphasis on sensitivity, Quality factor (Q-factor), Limit of Detection (LOD), and Figure of Merit (FOM). Our results reveal that the cone-like nanoshell significantly outperforms other geometries, achieving over five-fold improvement in FOM and a two-fold reduction in the LOD compared to conventional spherical designs, offering transformative potential for early cancer diagnostics. This enhancement is attributed to its sharp apex-driven plasmon resonance gradient, which facilitating enhanced electromagnetic field localization and a plasmon resonance gradient, which strengthens plasmon-exciton coupling. Specifically, the cone's geometry supports simultaneous longitudinal and transverse plasmon modes, minimizing plasmon damping and optimizing impedance matching, leading to a higher Q-factor and FOM. In contrast, elliptical nanoshells show reduced performance due to non-uniform field distribution and suboptimal plasmon-exciton interaction. These findings not only offer critical design guidelines for high-performance nanobiosensors but also open new avenues in label-free cancer diagnostics, environmental sensing, and nanophotonic device engineering.</p>

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Maxwell–Bloch FDTD study of plasmon–exciton coupling in geometry-optimized nanoshells for refractive index sensing

  • 期刊论文

  • 发表日期：

    2025年9月26日

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  • Arezoo Firoozi,
  • Ahmad Mohammadi,
  • Tahmineh Jalali

摘要

In this paper, we propose a novel design and analysis of nanobiosensors utilizing plasmon-exciton (plexciton) coupling in geometrically optimized core–shell nanoshells. They consist of a core of plasmonic nanoparticles coated with molecules as a shell with various geometrical configurations such as elliptical, spherical, nanorod, rounded cone-like, cone-like, and truncated cone-like nanoshells for advanced biosensing applications, particularly focusing on cancer detection. Through a semiclassical modeling approach combining classical electromagnetic field treatment with quantum emitter responses via the optical Bloch equation, we employ three-dimensional finite difference time domain (3D-FDTD) simulations of Maxwell-Bloch equations to investigate the optical properties and optical field distributions of these nanobiosensor designs. The effects of key parameters are investigated, including the core and shell geometrical parameters, quantum emitter parameters, and the refractive index of the surrounding media. These hybrid nanosensors are engineered to detect minute refractive index changes associated with cancer biomarkers, offering potential for early-stage diagnosis of five cancer types: skin, breast, adrenal gland, cervical, and blood cancer with particular emphasis on sensitivity, Quality factor (Q-factor), Limit of Detection (LOD), and Figure of Merit (FOM). Our results reveal that the cone-like nanoshell significantly outperforms other geometries, achieving over five-fold improvement in FOM and a two-fold reduction in the LOD compared to conventional spherical designs, offering transformative potential for early cancer diagnostics. This enhancement is attributed to its sharp apex-driven plasmon resonance gradient, which facilitating enhanced electromagnetic field localization and a plasmon resonance gradient, which strengthens plasmon-exciton coupling. Specifically, the cone's geometry supports simultaneous longitudinal and transverse plasmon modes, minimizing plasmon damping and optimizing impedance matching, leading to a higher Q-factor and FOM. In contrast, elliptical nanoshells show reduced performance due to non-uniform field distribution and suboptimal plasmon-exciton interaction. These findings not only offer critical design guidelines for high-performance nanobiosensors but also open new avenues in label-free cancer diagnostics, environmental sensing, and nanophotonic device engineering.