Abstract. We report energy transfer (ET) from two dyes: Alexa Fluor 514 (AF514) and Alexa Fluor 532 (AF532) to gold nanoparticles (AuNPs) of three different sizes (10, 30, and 53 nm) employing steady-state and time-resolved fluorescence measurements. The results show that the fluorescence intensity and fluorescence lifetimes of donor (D) molecules AF514 and AF532 decrease with increase in the concentration of acceptor (A) AuNPs (2 to 10 μM) upon interaction with AuNPs, thereby confirming the occurrence of ET between D and A. This clearly suggests that these two Alexa Fluor molecules act as efficient donors and AuNPs as excellent acceptors. Interestingly, the Forster distance (Ro) determined for these dyes varies from 212 to 550 Å with increasing size of AuNPs and suggests that the ET from AF514 and AF532 to AuNPs is essentially obeying surface energy transfer (SET) process following 1 / d4 distance dependence. As is well known, Forster resonance energy transfer is efficient for separation distances of up to 100 Å, beyond which its efficiency decreases. Thus, the present results follow dipole-surface type ET from molecule dipole (AF514 and AF532) to nanometal (Au) surface. The influence of size and distance on the SET from AF514 and AF532 to AuNPs is discussed. Further, the quenching of donor fluorescence in the presence of AuNPs and nonradiative ET are analyzed using Stern–Volmer plots. Our study is an experimental quest to explore the potential of such dye–noble metal NPs pairs performing as sensitive chemical and biosensors.

中文翻译：

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从 Alexa Fluor 染料到金纳米粒子的多供体表面能转移：对创新传感器应用的探索

摘要。我们报告了两种染料的能量转移 (ET)：Alexa Fluor 514 (AF514) 和 Alexa Fluor 532 (AF532) 到三种不同尺寸（10、30 和 53 nm）的金纳米粒子 (AuNPs)，采用稳态和时间-分辨荧光测量。结果表明，在与AuNPs相互作用时，供体（D）分子AF514和AF532的荧光强度和荧光寿命随着受体（A）AuNPs（2至10μM）浓度的增加而降低，从而证实了D之间发生ET和 A. 这清楚地表明这两个 Alexa Fluor 分子作为有效的供体和 AuNPs 作为优秀的受体。有趣的是，随着 AuNP 尺寸的增加，为这些染料确定的 Forster 距离 (Ro) 从 212 到 550 Å 变化，这表明从 AF514 和 AF532 到 AuNP 的 ET 基本上服从表面能转移 (SET) 过程，遵循 1 / d4 距离依赖性。众所周知，Forster 共振能量转移对于高达 100 Å 的分离距离是有效的，超过此距离其效率会降低。因此，目前的结果遵循从分子偶极子（AF514 和 AF532）到纳米金属 (Au) 表面的偶极子表面型 ET。讨论了尺寸和距离对从 AF514 和 AF532 到 AuNPs 的 SET 的影响。此外，使用 Stern-Volmer 图分析了在 AuNPs 和非辐射 ET 存在下供体荧光的猝灭。