Catalytic additives are widely employed to improve the sensing characteristics of oxide-based solid-state gas sensors. The most frequently used additives are noble metals such as Pt, Pd and Au. In thick film techniques, several wet methods to introduce the additives in the sensing oxide matrix have been proposed, most of which are based in two basic procedures: a) impregnation of the oxide with a salt solution of the additive followed by a heat treatment; and b) introduction of a salt of the additive during the synthesis of the oxide.In both cases the additive is introduced as a molecular species (PtCl₆^-2, PdCl₂, etc.), which undergoes a chemical change to its final form, presumably metallic clusters, during a pyrolitic process. However, the final chemical states associated to the additives and its localization in the oxide matrix are issues still under debate.
In this work an alternative approach to the introduction of the catalyst is presented; based in the incorporation of previously synthesized metallic nanoparticles in the formulation of the SnO₂ screen-printing paste. Two different methods of nanoparticles incorporation were used. In the first, the as-prepared metallic clusters, suspended in a stabilizing media, were directly incorporated in the screen-printing mix. In this case physical adsorption of the metal clusters to the oxide surface is expected. Alternatively the SnO₂ powders were funtionalized by means of a suitable monomolecular coupling layer, which captures the metal clusters by ligand coordination. The metal clusters-coordinated oxides were then used in the preparation of the screen-printing paste.The sensitive pastes thus obtained were screen-printed onto 96% alumina substrates.
The gas sensing properties of the sensors were studied and the influence of the nano-particles size, concentration and synthesis method in the response of the sensors are discussed.

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