Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, USA.
Nanoscale. 2012 Jul 21;4(14):4247-54. doi: 10.1039/c2nr30628j. Epub 2012 Jun 12.
Metal nanoclusters have interesting steady state fluorescence emission, two-photon excited emission and ultrafast dynamics. A new subclass of fluorescent silver nanoclusters (Ag NCs) are NanoCluster Beacons. NanoCluster Beacons consist of a weakly emissive Ag NC templated on a single stranded DNA ("Ag NC on ssDNA") that becomes highly fluorescent when a DNA enhancer sequence is brought in proximity to the Ag NC by DNA base pairing ("Ag NC on dsDNA"). Steady state fluorescence was observed at 540 nm for both Ag NC on ssDNA and dsDNA; emission at 650 nm is observed for Ag NC on dsDNA. The emission at 550 nm is eight times weaker than that at 650 nm. Fluorescence up-conversion was used to study the dynamics of the emission. Bi-exponential fluorescence decay was recorded at 550 nm with lifetimes of 1 ps and 17 ps. The emission at 650 nm was not observed at the time scale investigated but has been reported to have a lifetime of 3.48 ns. Two-photon excited fluorescence was detected for Ag NC on dsDNA at 630 nm when excited at 800 nm. The two-photon absorption cross-section was calculated to be ∼3000 GM. Femtosecond transient absorption experiments were performed to investigate the excited state dynamics of DNA-Ag NC. An excited state unique to Ag NC on dsDNA was identified at ∼580 nm as an excited state bleach that related directly to the emission at 650 nm based on the excitation spectrum. Based on the optical results, a simple four level system is used to describe the emission mechanism for Ag NC on dsDNA.
金属纳米团簇具有有趣的稳态荧光发射、双光子激发发射和超快动力学。一类新的荧光银纳米团簇（Ag NCs）是纳米团簇信标。纳米团簇信标由一个弱发光的 Ag NC 模板组成，该模板位于单链 DNA 上（“Ag NC on ssDNA”），当 DNA 增强序列通过 DNA 碱基配对靠近 Ag NC 时，它变得具有强荧光性（“Ag NC on dsDNA”）。对于 Ag NC on ssDNA 和 dsDNA，都观察到稳态荧光在 540nm 处发射；对于 Ag NC on dsDNA，观察到在 650nm 处发射。在 550nm 处的发射比在 650nm 处弱八倍。使用荧光上转换来研究发射的动力学。在 550nm 处记录了双指数荧光衰减，寿命为 1ps 和 17ps。在研究的时间尺度上没有观察到在 650nm 处的发射，但已经报道其寿命为 3.48ns。当在 800nm 处激发时，在 630nm 处检测到 Ag NC on dsDNA 的双光子激发荧光。计算出的双光子吸收截面约为 3000GM。进行飞秒瞬态吸收实验以研究 DNA-Ag NC 的激发态动力学。在 580nm 处鉴定到一种独特于 Ag NC on dsDNA 的激发态，它是一种激发态漂白，根据激发光谱，它与在 650nm 处的发射直接相关。基于光学结果，使用一个简单的四能级系统来描述 Ag NC on dsDNA 的发射机制。
