| A detailed review on the applications of conducting polymers in nanomaterials and on the development of polypyrrole (PPy) nanocomposite in electrochemical biosensors was carried out. The research work was focused on fabrication of electrochemical sensors by surface nano-construction using PPy and its overoxidized forms based on metal nanocomposites. Field emission scanning electron microscope, X-ray photoelectron spectroscopy, X-ray diffraction and electrochemical techniques were used to characterize structures and electrochemical sensing properties of these nanoelectrodes. The use of these electrodes in fuel cells (such as methanol, ethanol, formaldehyde and oxygen) and electrochemical sensing of substances involving of monoamine neurotransmitters (such as dopamine, epinephrine and serotonin) and other bioactive molecules (such as ascorbic acid, uric acid, glucose, nicotinamide adenine dinucleotide, hydrazine, hydroxylamine and nitrite) were investigated. The details are as follows:The PPy nanowires modified glassy carbon electrode (PPy/GCE) was directly electrodeposited without additional templates. Then, Pt nanoclusters were electrochemically deposited on PPy/GCE and PPy-Pt composite modified electrode (PPy-Pt/GCE) was obtained. The Pt nanoclusters with diameter of 100 nm were embedded in the PPy nanowires, forming a novel microporous structure nanocomposite. We found that the modified electrode has strongly electrocatalytic activity toward reactions of methanol, ethanol, formaldehyde, O2 and NO2-. Thus, it can be effectively used as high sensitive oxygen sensor and NO2- sensor, as well as the anode and cathode in fuel cells. The maximum current density of methanol oxidation reaction was 17.8 mA/cm2, which was 1.5 times of that at corresponding Pt/GCE. The CO poisoning effect on the electrode can be significantly reduced. The O2 reduction reaction at the electrode gave a cathodic peak at 0.518 V in H2SO4 solution with current density of 1.3 mA/cm2, which is much higher than that of the corresponding Pt/GCE.Then, a novel glucose biosensor (POAP-GOD/PPy-Pt/GCE) was fabricated by co-deposition of o-aminophenol and glucose oxidase on PPy-Pt/GCE. The sensor has superior sensing ability of amperometric response time of 7 s, the detection limit of 4.5×10-7 mol/L, the maximum current density of 378μA/cm2, the activation energy of 25.9 kJ/mol,and Michaelis-Menten constant of 23.9 mmol/L. It demonstrated that the PPy-Pt and POAP-GOD nanocomposite bilayer structure can completely eliminate the interference of ascorbic acid, uric acid and acetaminophen, and well maintain the enzyme activity and stability, enhancing both of the sensitivity and reproducibility.Alternatively, Au nanoparticles were electrochemically deposited on PPy/GCE, generating an Au/PPy nanocomposite modified GCE (Au/PPy/GCE), on which Au nanoparticles of about 15 nm in diameter were uniformly dispersed on the surface of PPy nanowires. The Au/PPy/GCE exhibited strongly catalytic activity toward the oxidation of hydrazine, hydroxylamine and nitrite. The sensor showed wide linear ranges, high sensitivities and low detection limits in the electrochemical sensing of these species.On the other hand, the conducting PPy film has been overoxidized in NaOH solution, generating a non-conducting PPyox film modified electrode (PPyox/GCE). Au nanoparticles were electrochemically deposited into the PPyox template and obtained a nano-Au array electrode (nano-Au/PPyox/GCE). Due to the synergic effect of nano-Au and PPyox template, the nanoelectrode exhibited excellent selectivity and sensitivity toward dopamine (DA), epinephrine (EP), serotonin (5-HT) and uric acid (UA) oxidation, which could eliminate the interferences of AA. The sensor has been applied to detect EP, DA, 5-HT and UA in the presence of high concentrations of AA.Finally, the electrochemical behavior of catechol at PPyox/GCE was investigated. The electrocatalytic oxidation of nicotinamide adenine dinucleotide (NADH) mediated by catechol has been examined. The interference of UA with NADH oxidation was eliminated.
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