Inkjet printing of room-temperature gas sensors for identification of formalin contamination in squids

Printed room temperature gas sensors based on 2D hybrid pristine, NH₂ and N₂ functionalized multi-wall carbon nanotubes (MWCNTs)/PEDOT:PSS conductive polymer were fabricated by inkjet printing technique. The electronic inks prepared from MWCNTs dispersion in PEDOT:PSS were printed over interdigitated silver electrodes on flexible and transparent substrates. Surface morphology and functionalization of fabricated sensors were characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The sensing properties of hybrid printed films were exposed to various volatile organic compounds and gases including formaldehyde, ethanol, methanol, ammonia, nitrogen dioxide and hydrogen sulfide at room temperature. The results show that PEDOT:PSS/MWCNTs-N₂ sensor exhibits the highest sensitivity and selectivity to formaldehyde in concentration range of 10–200 ppm at room temperature. The sensing mechanism of the fabricated sensors can be explained based on charge transfer process and the interaction between functional groups of CNTS and formaldehyde molecules. The theoretical calculation based on self-consistent charge density functional tight-binding (SCC-DFTB) was employed and confirmed the proposed sensing mechanism. Moreover, a real-world food application of a fabricated sensor array was demonstrated through identification of formalin contamination in squids based on electronic nose and principal component analysis (PCA) method. The PCA shows the perfect classification between pure and formalin contaminated squid samples as well as different percentages of contaminations.