Rapid progress of nanotechnology and advanced nanomaterials production over the past decade offer significant opportunities for a wide range of applications in many fields ranging from medical diagnostics, imaging and drug delivery to sensing, catalysis and environmental remediation. While many engineered nanomaterials are commonly used in commercial products, their interactions with biological systems, their transport, kinetic, toxicity and accumulation in living organisms as well as their environmental and health effects are largely unknown and their use has recently become of particular concern. Several studies have shown that there is a direct relationship between the nanomaterial’s structure and physicochemical properties and their impact in biological systems. The effect of NPs on biological systems varies broadly, and some reported results are contradictory, even in the case of the same type of materials. One of the key nanotoxicity mechanisms is the potential for induction of oxidative stress by generating nitrogen (RNS) species. However, assessing the extent of NPs induced oxidative stress has been a challenge as most RNS are highly reactive and short lived and therefore difficult to detect. We have developed electrochemical sensors for detection by direct real-time assessment of RNS species at the NPs accumulation site in living zebrafish embryos.