In this work, direct electrochemistry and electrocatalytic activity of four new kinds of artificially prepared superoxide dismutases (SODs) from human pathogen Clostridium difficile with different metal centers and microenvironments, that is, manganese superoxide dismutase (Mn-SOD), azide ion-coordinated manganese superoxide dismutase (Mn(N-3(-))-SOD), iron superoxide dismutase (Fe-SOD), and nickel superoxide dismutase (Ni-SOD), are systematically investigated. The direct electron transfer of the SODs is realized by 3-mercaptopropionic acid (MPA) confined on gold flowers electrodeposited onto glassy carbon electrode. The electrochemical parameters are dependent on the metal centers and microenvironments of the SODs with respect to the formal potential, reversibility of electrode reactions, and kinetic rate constant. Furthermore, except Ni-SOD, the other three kinds of SODs all exhibit a bifunctional electrocatalytic activity toward O-2(-). The combination of the enhanced electron transfer and the enzyme catalytic activities of SODs enables a sensitive and selective determination of O-2(-). (C) 2014 Elsevier B.V. All rights reserved.