Schulich Faculty of Chemistry , Technion - Israel Institute of Technology , Haifa 3200008 , Israel.
Department of Biomedical Engineering , Ohio State University , Columbus , Ohio 43210 , United States.
Anal Chem. 2018 Jul 3;90(13):7830-7836. doi: 10.1021/acs.analchem.8b00917. Epub 2018 Jun 13.
Electron spin resonance (ESR) is a powerful analytical technique used for the detection, quantification, and characterization of paramagnetic species ranging from stable organic free radicals and defects in crystals to gaseous oxygen. Traditionally, ESR requires the use of complex instrumentation, including a large magnet and a microwave resonator in which the sample is placed. Here, we present an alternative to the existing approach by inverting the typical measurement topology, namely placing the ESR magnet and resonator inside the sample rather than the other way around. This new development relies on a novel self-contained ESR sensor with a diameter of just 2 mm and length of 3.6 mm, which includes both a small permanent magnet assembly and a tiny (∼1 mm in size) resonator for spin excitation and detection at a frequency of ∼2.6 GHz. The spin sensitivity of the sensor has been measured to be ∼10 spins/√Hz, and its concentration sensitivity is ∼0.1 mM, using reference samples with a measured volume of just ∼10 nL. Our new approach can be applied for monitoring the partial pressure of oxygen in vitro and in vivo through its paramagnetic interaction with another stable radical, as well as for simple online quantitative inspection of free radicals generated in reaction vessels and electrochemical cells via chemical processes.
电子自旋共振（ESR）是一种强大的分析技术，用于检测、定量和表征从稳定的有机自由基和晶体缺陷到气态氧的顺磁物质。传统上，ESR 需要使用复杂的仪器，包括一个大磁铁和一个微波谐振器，样品放在其中。在这里，我们通过反转典型的测量拓扑结构，即把 ESR 磁铁和谐振器放在样品内部而不是外部，提供了一种替代现有方法的方案。这种新的发展依赖于一种新型的、自给自足的 ESR 传感器，直径只有 2 毫米，长度为 3.6 毫米，它包括一个小型的永磁体组件和一个微小的（尺寸约为 1 毫米）谐振器，用于在 2.6GHz 的频率下进行自旋激发和检测。通过使用体积仅约为 10nL 的参考样品，测量到传感器的自旋灵敏度约为 10 个自旋/√Hz，其浓度灵敏度约为 0.1mM。我们的新方法可以通过其与另一个稳定自由基的顺磁相互作用，应用于体外和体内监测氧分压，也可以通过化学反应，用于反应容器和电化学电池中生成的自由基的简单在线定量检查。
