电子顺磁共振（EPR）技术因其无创性、灵敏性及特异性，已发展为重要的氧测量及成像技术。近年来，四硫取代三苯甲基（TAM）自由基优越的波谱性质、高度的氧气敏感性及稳定性使其在EPR测氧和成像方面表现出极大的潜力。然而，原初TAM自由基的膜不可透性及合成方法的局限性制约了其在生物医学领域的广泛应用。鉴于此，本项目拟1）设计新的合成方法，开发两类新的TAM母体化合物并对其衍生化，构建高稳定、高灵敏、生物相容且分别靶向细胞质、线粒体或细胞外的氧探针；2）通过对探针物理化学性质的表征及在细胞和活体层面的性能测试，确定其最大使用剂量、体内分布、靶向性能与靶向机理等，总结出对氧探针的设计与合成具有指导意义的规律；3）以小鼠心肌缺血再灌注损伤模型为研究对象，阐明靶向探针在检测与成像细胞内外氧浓度以及浓度梯度的实用性，为该类氧探针在与氧相关疾病的发病机制研究及其诊治的应用前景提供直接的实验证据。

Owing to the noninvasive nature, sensitivity and specificity, electron paramagnetic resonance (EPR) spectroscopy/imaging in tandem with the use of exogenous paramagnetic probes, has been established as an important technique for the in vivo measurement and mapping of oxygen (O2). Unfortunately, the full potential of this technique has not been realized mainly due to lack of suitable paramagnetic probes. Recently, tetrathiatriarylmethyl (TAM) radicals show great potential in the EPR measurement and imaging of O2 owing to their unique sharp EPR singlet, high O2 sensitivity and biostability. However, their biomedical application has been hampered by the lack of affordable large-scale synthesis. In addition, the original TAMs are cell-impermeable due to their anionic state at physiological pH and thus their application is merely limited to the extracellular fluid. To address these, this proposal consists of a research plan of 3 aims: 1) to develop the new synthetic procedure enabling efficient synthesis and scale up for two TAM parent radicals with improved properties and then derivatize these two TAMs as novel high sensitivity oximetry probes with good biocompatibility for targeted extracellular or intracellular O2 measurement; 2) to physicochemically characterize these new oximetry probes and determine their maximal nontoxic doses, kinetics of uptake, metabolism and clearance as well as cellular and subcellular biodistribution in cells and mice; 3) to evaluate and apply TAM probes for in vivo targeted O2 measurement and imaging in mouse models of myocardial ischemia-reperfusion injury. Because of the central importance of O2 concentrations and localized concentration gradients in normal physiology and disease, these novel probes will uniquely provide critical information enabling the understanding of disease mechanisms leading to improved treatments.