Novel physically prpoduced porphyrin arrays for developing superior 'sensing eyes'

The generalized detection of volatile organic compounds (VOCs) is often referred to as electronic nose technology, and has generally been based on sensors that detect adsorption into a set of polymers or on electrochemical oxidations at a set of heated metal oxides [1]. In spite of some successes with such systems, the discrimination of compounds at low concentrations or within a given chemical class and the absence of interference from changes in humidity remain challenging goals. More recently it has been reported the production of a colorimetric array for detecting a wide range of odorants using metalloporphyrins [2]. The importance of using a porphyrinbased array is emphasized by the recent indications that the mammalian olfactory receptors are in fact metalloproteins [3]. In this work we show new highly metallo-porphyrin sensing units for developing more efficient colorimetric artificial sensor array (sensing eye). The most important novelty of this work is represented by the production The method of the thin film sensing elements: in fact, while conventional porphyrin units are deposited by chemical methods (i.e. spin coating), here we produced them by high vacuum evaporation technique (HVE). HVE takes several advantages as great reproducibility, higher uniformity, stricter control of the film thickness and, above all, better purity in comparison with standard chemical ones. It has been demonstrated that HVE technique, avoiding the unpredictable effects of the retained solvent molecules (i.e. occupation of adsoprtion sites, interference in the analyte/material interaction), allows to produce superior sensing elements than conventional ones [4]. In particular, in this work preliminary results on the physical characterization and sensing capabilities of the specific HVE units constituted by a series of tetraphenylporphyrins (H2TPP, CoTPP, Fe(TPP)Cl, CuTPP, NiTPP) are reported. The responses of the chemosensor array towards different VOC classes (alcohols, ketones, acids) are discussed by analyzing the optical changes of the specific units through principal component analysis (PCA). Finally the responses of our novel sensing array are compared to those of an analogous conventional one.