Surface Plasmon Resonance Enhanced Light Absorption and Photothermal Therapy in the Second Near-Infrared Window

TLDR

Localized surface plasmon resonance (LSPR) is well studied in noble metal nanoparticles, but its exploitation in doped nonmetallic nanomaterials and hybrid systems remains largely unexplored. The study aims to construct a dual plasmonic Au‑Cu₉S₅ hybrid to investigate LSPR coupling between metal and semiconductor oscillations and to guide future design of photoabsorbers and photothermal nanoheaters. A Au‑Cu₉S₅ nanosystem with precisely engineered interfaces was fabricated to probe the coupling of LSPR arising from collective electron and hole oscillations. Cu₉S₅ LSPR was enhanced by 50 % in the presence of Au, and simulations confirmed stronger local fields and higher optical absorption, leading to a 37 % photothermal conversion efficiency, deep 1064‑nm penetration, excellent X‑ray attenuation, low cytotoxicity, and enabling robust photothermal therapy and X‑ray CT imaging in the second NIR window at low dose and laser flux.

Abstract

Enhanced near-field at noble metal nanoparticle surfaces due to localized surface plasmon resonance (LSPR) has been researched in fields ranging from biomedical to photoelectrical applications. However, it is rarely explored on nonmetallic nanomaterials discovered in recent years, which can also support LSPR by doping-induced free charge carriers, let alone the investigation of an intricate system involving both. Here we construct a dual plasmonic hybrid nanosystem Au-Cu9S5 with well controlled interfaces to study the coupling effect of LSPR originating from the collective electron and hole oscillations. Cu9S5 LSPR is enhanced by 50% in the presence of Au, and the simulation results confirm the coupling effect and the enhanced local field as well as the optical power absorption on Cu9S5 surface. This enhanced optical absorption cross section, high photothermal transduction efficiency (37%), large light penetration depth at 1064 nm, excellent X-ray attenuation ability, and low cytotoxicity enable Au-Cu9S5 hybrids for robust photothermal therapy in the second near-infrared (NIR) window with low nanomaterial dose and laser flux, making them potential theranostic nanomaterials with X-ray CT imaging capability. This study will benefit future design and optimization of photoabsorbers and photothermal nanoheaters utilizing surface plasmon resonance enhancement phenomena for a broad range of applications.