-Chitosan microspheres of a small particle size and with good sphericity were prepared by a spraydrying method followed by treatment with a cross-linking agent. Owing to restrictions on the use of crosslinked chitosan microspheres in the pharmaceutical field, d,l-glyceraldehyde, a biocompatible reatant was used. The parameters studied affecting extent of cross-linking were cross-linking time and concentration of the cross-linking agent. Glutaraldehyde, the aldehyde most frequently employed as chemical cross-linking agent for proteins, was also used as a control. The cross-linked spray-dried chitosan microspheres were analyzed with respect to their morphological aspects, particle size, zeta potential and water uptake capacity. It was found that an increase either in d,l-glyceraldehyde concentration or in duration of cross-linking caused a decrease in both the swelling capacity and the zeta potential of the chitosan microspheres. Compared to glutaraldehyde, d,l-glyceraldehyde appears to be a good cross-linking agent for chitosan microspheres with the advantage that it is nontoxic.

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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.