Controlled synthesis of CuO with various hierarchical structures consisting of self-organized nanoparticles is realized by using n-octylamine (OLA) as a structure inducing agent via a facile hydrothermal synthetic method. The growth and assemblage of CuO can be finely tuned by selecting the preparative parameters. In particular, it is found that the degree of the hierarchical organization can be modulated by simply changing the amount of the n-octylamine and CuO nanoparticles exhibit self-assembled two-dimensional (2D) sheet-like, three-dimensional (3D) disk-like and bowknot-like architectures, respectively. In the present case, OLA serves as a capping surfactant that can modulate growth of CuO nanocrystals via hydrophobic forces between the OLA molecules. CuO nanoparticles can be self-assembled into different complex architectures depending on the strength of hydrophobic forces. Hierarchical sphere-like CuO assembled from nanorods can also be easily fabricated by adjusting the starting NaOH to CuCl2 volume ratio, in which OLA serves not only as the structure-directing agent, but also as a weak base agent to produce hydroxyl anions. The electrochemical performances of the as-synthesized different products for sensing nitrite oxidation are evaluated. The results reveal that the electrocatalytic activity is related to the secondary nanostructures. Compared to the others, the bowknot-shaped and sphere-shaped CuO products exhibit excellent electrocatalytic activity toward nitrite oxidation and fast current response in nitrite sensing because of their peculiar hierarchical structures with high BET surface areas and well-ordered pores. (C) 2013 Elsevier Inc. All rights reserved.