Zhang Jian, Fu Yi, Chowdhury Mustafa H, Lakowicz Joseph R
Center for Fluorescence Spectroscopy, University of Maryland School of Medicine, Department of Biochemistry and Molecular Biology, 725 West Lombard Street, Baltimore, Maryland 21201.
J Phys Chem C Nanomater Interfaces. 2007 Dec 11;112(1):18. doi: 10.1021/jp074938r.
We studied the dependence of single-molecule fluorescence on the size of nearby metal particles. The silver particles were synthesized with average diameters of metal cores being 5, 20, 50, 70, and 100 nm, respectively. A single-stranded oligonucleotide was chemically bound to a single silver particle and a Cy5-labeled complementary single-stranded oligonucleotide was hybridized with the particle-bound oligonucleotide. The space between the fluorophore and metal core was separated by a rigid hybridized DNA duplex of 8 nm length. The single fluorescence images and intensity traces were recorded by scanning confocal microscopy. The single fluorophore-labeled 50 nm silver particles displayed the most enhanced intensity, a factor of 17-fold increase relative to the free fluorophores in the absence of metal. Numerical simulations by the finite-difference time-domain (FDTD) method and results from Mie theory were used to compare with the experimental results. The 50 nm silver particles were also labeled by multiple fluorophores. The fluorescence intensity of multiple fluorophore-labeled metal particles increases dramatically with the loading number and reached 400-fold relative to the free single fluorophore when the loading number of fluorophore per metal particle was 50. The fluorophore also displayed better photostability when binding on the metal particle. These results can aid us to develop novel nanoscale fluorophores for clinical diagnostics and bioassay.
我们研究了单分子荧光对附近金属颗粒大小的依赖性。合成了平均金属核直径分别为5、20、50、70和100 nm的银颗粒。将一条单链寡核苷酸化学结合到单个银颗粒上，并使Cy5标记的互补单链寡核苷酸与颗粒结合的寡核苷酸杂交。荧光团与金属核之间的空间由长度为8 nm的刚性杂交DNA双链体隔开。通过扫描共聚焦显微镜记录单荧光图像和强度轨迹。单个荧光团标记的50 nm银颗粒显示出最强的强度增强，相对于无金属时的游离荧光团增加了17倍。使用时域有限差分（FDTD）方法进行的数值模拟和米氏理论的结果与实验结果进行比较。50 nm银颗粒也用多个荧光团标记。当每个金属颗粒的荧光团负载数为50时，多个荧光团标记的金属颗粒的荧光强度随着负载数急剧增加，相对于游离单荧光团达到400倍。荧光团在结合到金属颗粒上时也表现出更好的光稳定性。这些结果有助于我们开发用于临床诊断和生物测定的新型纳米级荧光团。
