Synthesis of Co(3)O(4) nanoparticles with block and sphere morphology, and investigation into the influence of morphology on biological toxicity.

In the present study, cobalt oxide (Co(3)O(4)) magnetic nanoparticles with block and sphere morphologies were synthesized using various surfactants, and the toxicity of the particles was analyzed by monitoring biomarkers of nanoparticle toxicity in zebrafish. The use of tartarate as a surfactant produced highly crystalline blocks of Co(3)O(4) nanoparticles with pores on the sides, whereas citrate lead to the formation of nanoparticles with a spherical morphology. Co(3)O(4) structure, crystallinity, size and morphology were studied using X-ray diffractogram and field emission scanning electron microscopy. Following an increase in nanoparticle concentration from 1 to 200 ppm, there was a corresponding increase in nitric oxide (NO) generation, induced by both types of nanoparticles [Co(3)O(4)-NP-B (block), r=0.953; Co(3)O(4)-NP-S (sphere), r=1.140]. Comparative analyses indicated that both types of nanoparticle produced significant stimulation at ≥5 ppm (P<0.05) compared with a control. Upon analyzing the effect of nanoparticle morphology on NO generation, it was observed that Co(3)O(4)-NP-S was more effective compared with Co(3)O(4)-NP-B (5 and 100 ppm, P<0.05; 200 ppm, P<0.01). Exposure to both types of nanoparticles produced reduction in liver glutathione (GSH) activity with corresponding increase in dose (Co(3)O(4)-NP-B, r=-0.359; Co(3)O(4)-NP-S, r=-0.429). However, subsequent analyses indicated that Co(3)O(4)-NP-B was more potent in inhibiting liver GSH activity compared with Co(3)O(4)-NP-S. Co(3)O(4)-NP-B proved to be toxic at 5 ppm (P<0.05) and GSH activity was almost completely inhibited at 200 ppm. A similar toxicity was observed with both types of Co(3)O(4)-NPs against brain levels of acetylcholinesterase (AChE; Co(3)O(4)-NP-B, r=-0.180; Co(3)O(4)-NP-S, r=-0.230), indicating the ability of synthesized Co(3)O(4)-NPs to cross the blood-brain barrier and produce neuronal toxicity. Co(3)O(4)-NP-B showed increased inhibition of brain AChE activity compared with Co(3)O(4)-NP-S (1,5, and 10 ppm, P<0.05; 50, 100 and 200 ppm, P<0.01). These results suggested that the morphology of nanoparticle and surface area contribute to toxicity, which may have implications for their biological application.