An ascorbic acid amperometric sensor using over-oxidized polypyrrole and palladium nanoparticles composites

We constructed a highly responsive ascorbic acid (AA) sensor utilizing over-oxidized polypyrrole (OPPy) and Palladium nanoparticles (PdNPs) composites (OPPy-PdNPs). In the presence of PdNPs, polypyrrole (PPy) was coated on a gold (Au) electrode through cyclic voltammetry (CV) and over-oxidized at a fixed potential in NaOH solution. The PdNPs were characterized using ultraviolet-visible (UV-vis) spectrum and transmission electron microscopy (TEM). The surface of OPPy-PdNPs on the Au electrode was investigated using field-emission scanning electron microscopy (FE-SEM). Results revealed that the OPPy-PdNPs-modified Au electrode (OPPy-PdNPs/Au) has the capacity to catalyze the oxidation of AA by lowering its oxidation potential to 0 V. The OPPy-PdNPs/Au electrode exhibited 2 different linear concentration ranges. In the low concentration range (1-520 mu M), OPPy-PdNPs/Au exhibited a direct linear relation with current responses and had high sensitivity (570 mu A mM(-1) cm(-2)) and a high correlation coefficient (0.995). In contrast, in the higher concentration range (120-1600 mu M), the relationship between current responses and concentration of AA can be represented by a two-parameter sigmoidal equation. In addition, the sensor exhibited a short response time (less than 2 s) and a very low limit of detection of 1 mu M. The electrochemical AA sensor constructed in this study was simple, inexpensive, reproducible, sensitive, and resistant to interference. Thus, the proposed sensor has great potential for detecting AA in complex biosystems and can be applied in various fields, particularly neuroscience. (C) 2012 Elsevier B.V. All rights reserved.