The adsorption of 4-nitrobenzenediazonium tetrafluoroborate (NBD) in acidic aqueous solution was investigated by scanning electrochemical microscopy (SECM) on polycrystalline gold and glassy carbon (GC) substrates. The feedback mode of SECM was used to study the local properties of each substrate before and after immersion in the aryldiazonium solution, by performing approach curves with two redox mediators, Fe(CN)(6)(4-) and Ru(NH(3))(6)(3+). The fitting of the approach curves with analytical approximate equation was used to evaluate the apparent heterogeneous rate constant k for Fe(CN)(6)(3-/4-) redox system at NBD-adsorbed GC (k = 2.6 x 10(-4) cm s(-1)). (C) 2010 Elsevier B.V. All rights reserved.