Detection of Authentication of Milk by Nanostructure Conducting Polypyrrole-ZnO

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 NaHCO_3.  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.