Gold nanoparticles (AuNPs, 2 similar to 5 nm in size) were facilely prepared by dispersing a pure gold wire with one-step anodic oxidation in an acidic solution containing Cl-and SnCl2. The formation processes of colloidal AuNPs, as investigated by in situ Raman spectra, mainly involved anodic dissolution of Au to AuCl4-, chemical reduction of AuCl4- to Au(0) by Sn(II) species and stabilization of AuNPs by the coadsorption of SnCl3- and Cl-. The residual Sn oxide layer can improve the stabilization of AuNPs. The resulting AuNPs showed high electrocatalytic activity toward the oxidation of ascorbic acid (AA) and were used for the electrochemical sensing of AA. Under the optimized condition, the detection method exhibited excellent performance with a wide linear range (0.1 mu M - 13 mM), high sensitivity (1033 mu A mM(-1) cm(-2)), low detection limit (0.06 mu M), long-term stability (over 24 days), and satisfactory quantification of AA concentration in medicine vitamin C tablets. (c) 2017 The Electrochemical Society. All rights reserved.