Department of Chemical Sciences, Università degli Studi di Padova, via Marzolo 1, 35131 Padova, Italy.
Department of Chemical Sciences, Università degli Studi di Padova, via Marzolo 1, 35131 Padova, Italy.
Prog Nucl Magn Reson Spectrosc. 2020 Apr;117:70-88. doi: 10.1016/j.pnmrs.2019.12.001. Epub 2019 Dec 21.
Sensing methodologies for the detection of target compounds in mixtures are important in many different contexts, ranging from medical diagnosis to environmental analysis and quality assessment. Ideally, such detection methods should allow for both identification and quantification of the targets, minimizing the possibility of false positives. With very few exceptions, most of the available sensing techniques rely on the selective interaction of the analyte with some detector, which in turn produces a signal as a result of the interaction. This approach hence provides indirect information on the targets, whose identity is generally ensured by comparison with known standards, if available, or by the selectivity of the sensor system itself. Pursuing a different approach, NMR chemosensing aims at generating signals directly from the analytes, in the form of a (complete) NMR spectrum. In this way, not only are the targets unequivocally identified, but it also becomes possible to identify and assign the structures of unknown species. In this review we show how relaxation- and diffusion-based NMR techniques, assisted by appropriate nanoparticles, can be used to edit the H NMR spectrum of a mixture and extract the signals of specific target compounds. Monolayer-protected nanoparticles, in particular those made from gold, are well suited to this task because they provide a versatile, protein-size support to build or incorporate supramolecular receptors. Remarkably, the self-organized and multifunctional nature of the nanoparticle coating allows exploitation of different kinds of non-covalent interactions, to provide tailored binding sites for virtually any class of molecules. From the NMR standpoint, the reduced translational and rotational diffusion rates of bulky nanoparticles offer a way to manipulate the states of the monolayer spins and build a reservoir of magnetization that can be selectively transferred to the interacting analytes. In addition, the low correlation time and the enhanced rigidity of the coating molecules (due to their grafting and crowding on the particle surface) promote efficient spin diffusion, useful in saturation transfer experiments. The optimized combination of NMR experiments and nanoreceptors can ultimately allow the detection of relevant analytes in the micromolar concentration range, paving the way to applications in the diagnostic field and beyond.
混合物中目标化合物的检测传感方法在许多不同的领域都很重要，从医学诊断到环境分析和质量评估。理想情况下，这种检测方法应该能够同时识别和定量目标物，最大限度地减少假阳性的可能性。除了极少数例外，大多数现有的传感技术都依赖于分析物与某些探测器的选择性相互作用，探测器的相互作用会产生信号。这种方法提供了关于目标物的间接信息，其身份通常通过与已知标准进行比较来保证，如果有的话，或者通过传感器系统本身的选择性来保证。NMR 化学传感采用了不同的方法，旨在直接从分析物中生成信号，形式为（完整的）NMR 谱。通过这种方式，不仅可以明确识别目标物，还可以识别和分配未知物质的结构。在这篇综述中，我们展示了如何利用基于弛豫和扩散的 NMR 技术，辅以适当的纳米粒子，来编辑混合物的 H NMR 谱，并提取特定目标化合物的信号。特别是由金制成的单层保护纳米粒子非常适合这项任务，因为它们为构建或纳入超分子受体提供了一种通用的、蛋白质大小的支撑。值得注意的是，纳米粒子涂层的自组织和多功能性质允许利用不同类型的非共价相互作用，为几乎任何一类分子提供定制的结合位点。从 NMR 的角度来看，大体积纳米粒子的低平移和旋转扩散率提供了一种操纵单层自旋状态的方法，并构建了一个可以选择性转移到相互作用分析物的磁化储备。此外，由于其在粒子表面的接枝和拥挤，涂层分子的低相关时间和增强的刚性促进了有效的自旋扩散，这在饱和转移实验中很有用。NMR 实验和纳米受体的最佳组合最终可以允许在微摩尔浓度范围内检测到相关的分析物，为诊断领域及其他领域的应用铺平道路。
