Controlled Incorporation of Silver Nanoparticles into Layer-by-Layer Polymer Films for Reusable Electronic Tongues

The incorporation of metallic nanoparticles in sensors and biosensors normally enhances performance, but fabricating reproducible sensing units is still an issue owing to the poor control of their electrical properties. In this article, we exploit the controlled deposition of silver nanoparticles (NP) preformed in a gas phase into layer-by-layer (LbL) films of poly(allylamine hydrochloride) (PAH) and poly(sodium 4-styrenesulfonate) (PSS) (PAH/PSS) assembled on gold interdigitated electrodes (IDEs). In situ impedance measurements during NP deposition allowed monitoring of the electrical response evolution, and reproducible sensing units could be made with tailored characteristics by varying the deposition time. In proof-of-principle experiments, we employed an array with four sensing units in an electronic tongue (e-tongue), which was capable of distinguishing basic flavors of the human palate and diverse commercial umami-based flavor enhancers. Using statistical analysis methods, it was possible to identify ways to optimize the e-tongue performance, thus confirming the possibility to explore controlled changes in electrical response via nanoparticle incorporation. It is worth noting that the methodology can be extended to produce other polymer-metallic NP composites and modify the electrical behavior of films in a controlled, reproducible manner, opening the way for enhanced optoelectronic devices, not limited to sensors or biosensors.