In Situ Electrochemical Scanning Tunnelling Microscopy Investigation of Structure for Horseradish Peroxidase and its Electrocatalytic Property

  • Zhang J
  • Chi Q
  • Dong S
 et al. 
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Abstract

Immobilization of protein molecules is a fundamental problem for scanning tunnelling microscopy ({STM}) measurements with high resolution. In this paper, an electrochemical method has been proved to be an effective way to fix native horseradish peroxidase ({HRP}) as well as inactivated {HRP} from electrolyte onto a highly oriented pyrolytic graphite ({HOPG}) surface. This preparation is suitable for both ex situ and in situ electrochemical {STM} ({ECSTM}) measurements. In situ {STM} has been successfully employed to observe totally different structures of {HRP} in three typical cases: (1) in situ {ECSTM} reveals an oval-shaped pattern for a single molecule in neutral buffer solution, which is in good agreement with the dimension determined as 6.2 x 4.3 x 1.2. nm(3) by ex situ {STM} for native {HRP}; (2) in situ {ECSTM} shows that the adsorbed {HRP} molecules on {HOPG} in a denatured environment exhibit swelling globes at the beginning and then change into a V-shaped pattern after 30 min; (3) in situ {ECSTM} reveals a black hole in every ellipsoidal sphere for inactivated {HRP} in strong alkali solution. The cyclic voltammetry results indicate that the adsorbed native {HRP} can directly catalyse the reduction of hydrogen peroxide, demonstrating that a direct electron transfer reduction occurred between the enzyme and {HOPG} electrode, whereas the corresponding cyclic voltammograms for denatured {HRP} and inactivated {HRP} adsorbed on {HOPG} electrodes indicate a lack of ability to catalyse H2O2 reduction, which confirms that the {HRP} molecules lost their biological activity. Obviously, electrochemical results powerfully support in situ {STM} observations.

Author-supplied keywords

  • Electrocatalysis
  • acid
  • activation
  • atomic force microscopy
  • carbon electrodes
  • dna
  • electrocatalysis
  • graphite ({HOPG})
  • highly oriented
  • highly oriented graphite ({HOPG})
  • horseradish peroxidase
  • in situ {STM}
  • mechanism
  • molecular-structure
  • oriented pyrolytic-graphite
  • surface
  • tunneling-microscopy
  • {DNA}

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Authors

  • J D Zhang

  • Q J Chi

  • S J Dong

  • E K Wang

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