Double fluorescent immunostaining with ER marker (e.g. Calnexin, Epoxide Hydrolase, especially "484" is recommended...) and DCFDA would be useful. However, you have to distinguish the pathological siginificance of ER stress and oxidative stress.ER stress is mainly caused by accumulation of proteins with abnormal conformational 3D structure, also referred to as misfolding. In contrast, redox stress is attenuated by glutatione and metabolic reprogramming in mitchondrial and cytosol.