Electron donor–acceptor effect-induced organic/inorganic nanohybrids with low energy gap for highly efficient photothermal therapy

For the design and optimization of near-infrared photothermal nanohybrids, tailoring the energy gap of nanohybrids plays a crucial role in attaining a satisfactory photothermal therapeutic efficacy for cancer and remains a challenge. Herein, we report an electron donor−acceptor effect-induced organic/ inorganic nanohybrid with a low energy gap (denoted as ICG/Ag/ LDH) by the in situ deposition of Ag nanoparticles onto the CoAl−LDH surface, followed by the coupling of ICG. A combination study verifies that the supported Ag nanoparticles as the electron donor (D) push electrons into the conjugated system of ICG by the electronic interaction between ICG and Ag, while OH groups of LDHs as the electron acceptor (A) pull electrons from the conjugated system ofICG by hydrogen bonding (N···H−O). This induces the formation of the D−A conjugated π-system and has a strong influence on the π-conjugated system of ICG, thus leading to a prominent decrease toward the energy gap and correspondingly an ultra-long redshift (∼115 nm). The resulting ICG/Ag/LDHs show an enhanced photothermal conversion efficiency (∼45.5%) at 808 nm laser exposure, which is ∼1.6 times larger than that of ICG (∼28.4%). Such a high photothermal performance is attributed to the fact that ICG/Ag/LDHs possess aD−π−A hybrid structure and a resulting lower energy gap, thus effectively promoting nonradiative transitions and leading to enhancement of the photothermal effect. Both in vitro and in vivo results confirm the good biocompatible properties and capability of the ICG/Ag/LDHs for NIR-triggered cancer treatment. This research demonstrates a successful paradigm for the rational design and preparation of new nanohybrids through the modulation of electron donor−acceptor effect, which offers a new avenue to achieve efficient phototherapeutic agent for improving the cancer therapeutic outcomes.

在近红外光热纳米杂化物（near-infrared photothermal nanohybrids）的设计与优化中，调控纳米杂化物的能隙对于获得理想的癌症光热治疗疗效至关重要，但这仍是一大挑战。本文报道了一种通过电子供体-受体效应诱导形成的低能隙有机/无机纳米杂化物（记为ICG/Ag/LDH）：其制备过程为在CoAl-LDH表面原位沉积银纳米颗粒（Ag nanoparticles），随后偶联吲哚菁绿（ICG）。联合研究证实，负载的银纳米颗粒作为电子供体（D），通过ICG与Ag之间的电子相互作用将电子推向ICG的共轭体系；而LDH的羟基（OH）作为电子受体（A），通过氢键（N···H−O）从ICG的共轭体系中拉取电子。这一效应诱导形成了D−π−A杂化结构，并对ICG的共轭体系产生强烈影响，从而显著降低能隙，且相应产生超长按移（redshift，约115 nm）。所得ICG/Ag/LDH在808 nm激光照射下表现出增强的光热转换效率（约45.5%），约为ICG本身（约28.4%）的1.6倍。如此优异的光热性能归因于ICG/Ag/LDH具有D−π−A杂化结构及由此产生的低能隙，从而有效促进非辐射跃迁（nonradiative transitions），增强光热效应。体内外实验结果均证实，ICG/Ag/LDH具有良好的生物相容性，且具备近红外（NIR）触发癌症治疗的能力。本研究展示了通过调控电子供体-受体效应合理设计与制备新型纳米杂化物的成功范式，为开发高效光治疗剂（phototherapeutic agent）以改善癌症治疗效果提供了新途径。