Leung Kam
National Center for Biotechnology Information, NLM, NIH
Optical fluorescence imaging is increasingly used to monitor biological functions of specific targets (1-3). However, the intrinsic fluorescence of biomolecules poses a problem when fluorophores that absorb visible light (350–700 nm) are used. Near-infrared (NIR) fluorescence (700–1,000 nm) detection avoids the background fluorescence interference of natural biomolecules, providing a high contrast between target and background tissues. NIR fluorophores have a wider dynamic range and minimal background as a result of reduced scattering compared with visible fluorescence detection. They also have high sensitivity, resulting from low infrared background, and high extinction coefficients, which provide high quantum yields. The NIR region is also compatible with solid-state optical components, such as diode lasers and silicon detectors. NIR fluorescence imaging is becoming a noninvasive alternative to radionuclide imaging in small animals (4, 5). Gold nanoparticles have been studied as molecular imaging agents because of their bright NIR fluorescence emission around 800 nm and low toxicity (6, 7). They can be tuned to emit in a range of wavelengths by changing their sizes, shapes, and composition, thus providing broad excitation profiles and high absorption coefficients. They can be coated and capped with hydrophilic materials for additional conjugation with biomolecules, such as peptides, antibodies, nucleic acids, and small organic compounds for and studies. Gold nanoparticles are approved by the United States Food and Drug Administration for treatment of patients with rheumatoid arthritis. Gold nanoclusters (AuNCs) possess an ultrasmall size of ~2 nm compared with quantum dots (QDs, ~20 nm) (8). AuNCs are less likely to have high reticuloendothelial system accumulation. AuNCs have been studied as agents for NIR fluorescence imaging of cancerous tissues through the enhanced permeability and retention effect (9).
光学荧光成像越来越多地用于监测特定靶点的生物学功能(1 - 3)。然而，当使用吸收可见光(350 - 700 nm)的荧光团时，生物分子的固有荧光会带来问题。近红外(NIR)荧光(700 - 1000 nm)检测可避免天然生物分子的背景荧光干扰，在靶组织和背景组织之间提供高对比度。与可见荧光检测相比，近红外荧光团由于散射减少而具有更宽的动态范围和最小的背景。它们还具有高灵敏度，这源于低红外背景，以及高消光系数，从而提供高量子产率。近红外区域也与固态光学组件兼容，如二极管激光器和硅探测器。近红外荧光成像正成为小动物放射性核素成像的一种非侵入性替代方法(4,5)。金纳米颗粒因其在800 nm左右明亮的近红外荧光发射和低毒性而被研究作为分子成像剂(6,7)。通过改变其尺寸、形状和组成，它们可以被调谐以在一系列波长下发射，从而提供宽激发谱和高吸收系数。它们可以用亲水材料包被和封端，以便与生物分子如肽、抗体、核酸和小有机化合物进行额外的缀合，用于[具体研究内容未给出]研究。金纳米颗粒已被美国食品药品监督管理局批准用于治疗类风湿性关节炎患者。与量子点(约20 nm)相比，金纳米团簇(AuNCs)的尺寸超小，约为2 nm(8)。金纳米团簇不太可能在网状内皮系统中大量蓄积。通过增强的渗透和滞留效应，金纳米团簇已被研究作为癌组织近红外荧光成像的试剂(9)。
