Mode-Dependent Energy Redistribution in Au Nanohole Arrays for Concurrent Photothermal Conversion and Reduced Fluorescence Quenching

초록

Plasmonic nanostructures simultaneously provide electric field enhancement and photothermal conversion, yet strong optical absorption for light-to-heat conversion increases nonradiative metal losses, which induce fluorescence quenching. Here, we propose a rational design strategy to mitigate this trade-off through mode-dependent sublayer energy redistribution in Au nanohole arrays. Electromagnetic simulations reveal dual surface plasmon resonance peaks whose spectral positions are governed by nanohole diameter and porosity. Under the optimized condition (160 nm diameter and 20% porosity), excitation at the longer-wavelength resonance (~670 nm) concentrates optical absorption predominantly in the bottom Au sublayer, with comparable electric field norm but ~3.4-fold lower absorptance in the top Au sublayer. This spatial separation suppresses non-radiative dissipation near emitters without sacrificing photothermal efficiency. Heat transfer simulations predict rapid temperature elevation to 95 °C within 100 s. An electric dipole model for a representative case (q0 = 0.7, distance = 5 nm) yields a 35.8-fold higher fluorescence enhancement at the longer-wavelength resonance than at the shorter-wavelength resonance (~550 nm), due to reduced quenching. Furthermore, bimetallic Ag–Au configurations demonstrate additional tunability of absorption distribution. The proposed design framework provides a physically grounded guideline for integrating photothermal control with reduced fluorescence quenching in a single plasmonic substrate.

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