Detection of Authentication of Milk by Nanostructure Conducting Polypyrrole-ZnO

Abstract

In this work, we developed a micro-scale smart gas sensor based on polypyrrole-ZnO (PPy-ZnO) fiber for the detection of some volatile compounds that were added as adulterants in milk samples. The PPy-ZnO nanocomposite was synthesized via a chemical polymerization method on polyester textile fiber, in which ZnO nanoparticles as dopant and FeCl3 as an oxidizing agent were used in nanocomposite polymerization. The structure and morphology of PPy-ZnO nanocomposite (30-100 nm) was studied by scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR). The designed PPy-ZnO fiber was used as a micro-scale gas sensor for rapid and simultaneous detection of adulterants added to milk samples. Adulterants in this study included NaClO, H2CO3, citric acid and NaHCO3. Central composite design (CCD) was used to study the effects of NaClO, H2CO3, citric acid and NaHCO3 concentration on the sensor responses to determine the adulteration in milk samples. Milk samples with different concentrations of adulterants (0-10 parts per thousand (g/L)) were prepared, and their volatile compounds, separated by the headspace method, were injected into the sensor. The PPy-ZnO sensor responses to volatile compounds of milk samples were analyzed by response surface methodology (RSM). Results showed that NaClO, H2CO3, citric acid and NaHCO3concentration affected the PPy-ZnO sensor responses, and there was a good linear relationship between the concentration of the adulterants and the sensor responses. The presented micro-scale smart gas sensor could detect adulteration by these chemicals in milk. The detection procedure was simple and rapid, and could be completed in 3 min following a 4 min sample preparation time.