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

In the present study, cobalt oxide ([Co.sub.3][O.sub.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.sub.3][O.sub.4] nanoparticles with pores on the sides, whereas citrate lead to the formation of nanoparticles with a spherical morphology. [Co.sub.3][O.sub.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.sub.3][O.sub.4]-NP-B (block), r=0.953; [Co.sub.3][O.sub.4]-NP-S (sphere), r=1.140]. Comparative analyses indicated that both types of nanoparticle produced significant stimulation at ≥ 5 ppm (P