Department of Chemical Engineering University of, Louisville, KY 40292, United States.
Anal Chim Acta. 2011 Jun 10;695(1-2):96-104. doi: 10.1016/j.aca.2011.03.058. Epub 2011 Apr 7.
Fluorescent contrast agents with high specificity and sensitivity are valuable for accurate disease detection and diagnosis. Spherical gold nanoparticles (GNPs) can be smartly utilized for developing highly effective agents. The strong electromagnetic (plasmon) field on their surface can be very effective in influencing the electrons of fluorophores and, thus, manipulating the fluorescence output (i.e., either quenching or enhancement). Fluorescence quenching can be used for negative sensing, or for conditional de-quenching to increase the specificity. Fluorescence enhancement allows sensing to be more sensitive. The level of fluorescence alteration depends on the GNP size, the excitation and emission wavelengths and quantum yield of the fluorophore, and the distance between the GNP and the fluorophore. To understand the mechanisms of the fluorescence change by GNP, we have theoretically analyzed the parameters involved in the fluorescence alteration for commonly used fluorophores, with an emphasis on quenching. The results showed that the fluorescence of fluorophores with the excitation (Ex) and emission (Ex) wavelengths close to the GNP resonance peak tended to be significantly quenched by GNPs. For those fluorophores emitting fluorescence in red or near infrared, to achieve quenching, the distance between GNP and the fluorophore was required to be very short. In general, a shorter distance resulted in more quenching. Bigger GNPs require a shorter distance to achieve the same level of quenching. The fluorescence of a fluorophore with a lower quantum yield (especially the one with emission in far-red or near-infrared) is more difficult to be quenched by GNPs (requires very short distance). Instead, it can be enhanced. Based on the theoretical study, we have developed a near-infrared contrast agent, i.e., Cypate conjugated GNP via a short peptide spacer. Normally the fluorescence of Cypate was quenched. The spacer has a motif of a substrate for urokinase type plasminogen activator (uPA; cancer-secreting enzyme). This contrast agent emits fluorescence only in the presence of uPA, where the uPA cleaves the spacer. This design can be used in characterization of the cancer type and also in diagnosing other diseases with signature enzymes.
具有高特异性和灵敏度的荧光对比剂对于准确的疾病检测和诊断非常有价值。球形金纳米粒子（GNPs）可以被巧妙地用于开发高效的试剂。它们表面的强电磁场（等离子体）可以非常有效地影响荧光团的电子，从而操纵荧光输出（即猝灭或增强）。荧光猝灭可用于负向感应，或用于条件去猝灭以提高特异性。荧光增强可使感应更灵敏。荧光变化的程度取决于 GNP 的大小、荧光团的激发和发射波长以及量子产率，以及 GNP 和荧光团之间的距离。为了理解 GNP 引起的荧光变化机制，我们从理论上分析了常用荧光团的荧光改变涉及的参数，重点是猝灭。结果表明，激发（Ex）和发射（Ex）波长接近 GNP 共振峰的荧光团的荧光往往会被 GNPs 显著猝灭。对于那些发射红色或近红外荧光的荧光团，为了实现猝灭，GNP 和荧光团之间的距离必须非常短。一般来说，距离越短，猝灭效果越明显。更大的 GNPs 需要更短的距离才能达到相同的猝灭水平。量子产率较低的荧光团（尤其是发射远红或近红外荧光的荧光团）的荧光更难被 GNPs 猝灭（需要非常短的距离），相反，它可以被增强。基于理论研究，我们开发了一种近红外对比剂，即通过短肽间隔物连接的 Cypate 共轭 GNP。通常 Cypate 的荧光被猝灭。间隔物具有尿激酶型纤溶酶原激活剂（uPA；癌症分泌酶）的底物的基序。这种对比剂只有在存在 uPA 的情况下才会发出荧光，uPA 会在这种情况下切割间隔物。这种设计可用于癌症类型的特征描述，也可用于诊断具有特征酶的其他疾病。
