Optical Sciences Division, Code 5611, U.S. Naval Research Laboratory, Washington, DC 20375, USA.
ACS Nano. 2012 Jun 26;6(6):5330-47. doi: 10.1021/nn301177h. Epub 2012 Jun 7.
The ability of luminescent semiconductor quantum dots (QDs) to engage in diverse energy transfer processes with organic dyes, light-harvesting proteins, metal complexes, and redox-active labels continues to stimulate interest in developing them for biosensing and light-harvesting applications. Within biosensing configurations, changes in the rate of energy transfer between the QD and the proximal donor, or acceptor, based upon some external (biological) event form the principle basis for signal transduction. However, designing QD sensors to function optimally is predicated on a full understanding of all relevant energy transfer mechanisms. In this report, we examine energy transfer between a range of CdSe-ZnS core-shell QDs and a redox-active osmium(II) polypyridyl complex. To facilitate this, the Os complex was synthesized as a reactive isothiocyanate and used to label a hexahistidine-terminated peptide. The Os-labeled peptide was ratiometrically self-assembled to the QDs via metal affinity coordination, bringing the Os complex into close proximity of the nanocrystal surface. QDs displaying different emission maxima were assembled with increasing ratios of Os-peptide complex and subjected to detailed steady-state, ultrafast transient absorption, and luminescence lifetime decay analyses. Although the possibility exists for charge transfer quenching interactions, we find that the QD donors engage in relatively efficient Förster resonance energy transfer with the Os complex acceptor despite relatively low overall spectral overlap. These results are in contrast to other similar QD donor-redox-active acceptor systems with similar separation distances, but displaying far higher spectral overlap, where charge transfer processes were reported to be the dominant QD quenching mechanism.
荧光半导体量子点（QD）与有机染料、光捕获蛋白、金属配合物和氧化还原活性标记物的多种能量转移过程的能力，继续激发人们开发它们用于生物传感和光捕获应用的兴趣。在生物传感配置中，基于某些外部（生物）事件，QD 与近端供体或受体之间能量转移速率的变化构成了信号转导的原理基础。然而，设计 QD 传感器以最佳方式发挥作用，前提是充分了解所有相关的能量转移机制。在本报告中，我们研究了一系列 CdSe-ZnS 核壳 QD 与氧化还原活性锇（II）多吡啶配合物之间的能量转移。为了促进这一点，将 Os 配合物合成作为反应性异硫氰酸酯，并用于标记六组氨酸末端肽。Os 标记的肽通过金属亲和配位比计量自组装到 QD 上，使 Os 配合物靠近纳米晶体表面。用不同发射最大值的 QD 组装具有增加比例的 Os-肽复合物，并进行详细的稳态、超快瞬态吸收和荧光寿命衰减分析。尽管存在电荷转移猝灭相互作用的可能性，但我们发现 QD 供体与 Os 配合物受体之间发生了相对有效的Förster 共振能量转移，尽管总体光谱重叠度相对较低。这些结果与其他具有相似分离距离但显示出更高光谱重叠度的类似 QD 供体-氧化还原活性受体系统形成对比，在这些系统中，电荷转移过程被报道为 QD 猝灭的主要机制。
