Electron Paramagnetic Resonance/Electron Spin Resonance

Electron spin resonance (ESR), also known as electron proton resonance (EPR), is a technique used to study the chemical species exhibiting unpaired electrons. EPR spectroscopy allows for the understanding of the function of organic and inorganic radicals as well as transition metal complexes. It can be particularly useful for studying oxidative stress (OS) in biological samples. Reactive species (RS) can be directly measured by EPR most often coupled to sensors to increase their lifetime and the sensitivity of the method. EPR techniques are known to be powerful in detecting primarily RS with properties similar to radicals such as O2•−, OH•, and NO•. EPR techniques have been developed for non-invasive detection of these RS in accessible sites such as human skin. They have been successfully applied in several other models using specific probes. There are three major approaches for RS detection using EPR technology with probes: spin trapping, spin formation, and spin quenching. In this chapter, we describe these approaches for the detection of RS. We capture the state of development of this expanding field, covering many important topics from immune-spin trapping to nanosensors. Recent advances in the application of sensitive and noninvasive EPR to intact cells and organs are brought into focus here.