Lustig Danielle R, Nilsson Zach N, Mulvey Justin T, Zang Wenjie, Pan Xiaoqing, Patterson Joseph P, Sambur Justin B
Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523-1872, United States.
Center for Complex and Active Materials, University of California, Irvine, Irvine, California 92697-2025, United States.
Chem Biomed Imaging. 2023 Apr 4;1(2):168-178. doi: 10.1021/cbmi.3c00015. eCollection 2023 May 22.
Defect-mediated energy transfer is an energy transfer process between midgap electronic states in a semiconductor nanocrystal (NC) and molecular acceptors, such as fluorescent dye molecules. Super-resolution fluorescence microscopy represents an exciting technique for pinpointing the nanoscale positions of lattice defect sites in, for example, a micrometer-sized particle or thin film sample by spatially resolving the location of the acceptor dye molecules with nanometer resolution. Toward this goal, our group performed ensemble-level, time-resolved fluorescence spectroscopy measurements of ZnO NC/Alexafluor 555 (A555) mixtures and calculated that the emissive defect sites are located, on average, 0.5 nm from the NC surface [Nilsson Z. N.; J. Chem. Phys.2021, 154 ( (5), ), 054704]. However, ensemble-level measurements cannot spatially resolve the defect sites on single particles, nor can they distinguish between surface-adsorbed dye molecules that participate in the energy transfer (EnT) process from those that do not. In this work, we compared the photoluminescence intensity trajectories of 789 isolated, single ZnO NC donors to those of 73 non-specifically bound and five specifically bound ZnO NC/A555 pairs, where the donor and acceptor centroid positions were separated by a distance that was smaller than our localization precision (40 nm). We observed minor fluorescence intensity fluctuations in the donor and defect channels instead of clear anticorrelated intensity fluctuations, which could be explained by (1) the presence of multiple emissive defect sites per NC, (2) donor-acceptor separation distances slightly larger than the Förster radius ( = 3.1 nm; defined as the distance at which EnT is 50% efficient), and/or (3) poor dipole-dipole coupling. The single molecule imaging methodology we developed, an alternating ultraviolet-visible excitation sequence combined with multicolor photon detection, successfully distinguishes specifically bound and non-specifically bound NC/dye pairs and can be applied to study a wide range of hybrid NC/dye energy transfer systems.
缺陷介导的能量转移是半导体纳米晶体（NC）中间隙电子态与分子受体（如荧光染料分子）之间的能量转移过程。超分辨率荧光显微镜是一种令人兴奋的技术，通过以纳米分辨率在空间上解析受体染料分子的位置，来精确确定例如微米级颗粒或薄膜样品中晶格缺陷位点的纳米级位置。为了实现这一目标，我们小组对ZnO NC/ Alexafluor 555（A555）混合物进行了整体水平的时间分辨荧光光谱测量，并计算出发光缺陷位点平均距离NC表面0.5 nm [Nilsson Z. N.; J. Chem. Phys.2021, 154 ( (5), ), 054704]。然而，整体水平的测量无法在空间上解析单个颗粒上的缺陷位点，也无法区分参与能量转移（EnT）过程的表面吸附染料分子和不参与该过程的分子。在这项工作中，我们比较了789个孤立的单个ZnO NC供体与73个非特异性结合和5个特异性结合的ZnO NC/A555对的光致发光强度轨迹，其中供体和受体质心位置之间的距离小于我们的定位精度（40 nm）。我们在供体和缺陷通道中观察到轻微的荧光强度波动，而不是清晰的反相关强度波动，这可以通过以下原因来解释：（1）每个NC存在多个发光缺陷位点；（2）供体-受体分离距离略大于Förster半径（= 3.1 nm；定义为EnT效率为50%时的距离）；和/或（3）偶极-偶极耦合不良。我们开发的单分子成像方法，即交替紫外-可见激发序列与多色光子检测相结合，成功地区分了特异性结合和非特异性结合的NC/染料对，并且可以应用于研究广泛的混合NC/染料能量转移系统。
