The Chemical Sensitivity of Hybrid Porphyrin Materials
Authors: Magna Gabriele , Stefanelli Manuela , Paolesse Roberto , Di Natale Corrado 
Published: July 2022

Porphyrins and corroles have been used in the last two decades to prepare sensor arrays for a variety of applications [1]. The wide chemical interactivity of these porphyrinoids sustains these applications making possible the measurement of complex patterns of volatile compounds. The interplay between the metal ion, the aromatic ring and the peripheral compounds establishes unique selectivity patterns which are fundamental elements for sensor array design and development. Films of porphyrins and corroles can be adequately applied to inorganic surfaces making possible the preparation of different kinds of chemical sensors. Among them mass transducers, such as Quartz Microbalances (QMBs), have been found particularly suitable for several applications. QMBs do not select the different interaction mechanisms, thus this transducer offer the unique chance to investigate the whole bouquet of interactions established between the volatile compounds and the sensitive layers. Porphyrins and corroles coated QMB sensor arrays have been successfully used in several application in particular to investigate in humans the relationships between volatilome and pathologies. Results include the diagnosis of lung cancer from breath [2], kidney cancer from urines [3], and COVID-19 from blood serum [4].
In the last years, we have been interested in replicating the behavior of QMB sensor arrays with other transduction principle which enables a more simple sensor system design and even the integration of sensors in wearable supports. To this regard the simplest sensor is that based on electric impedance variation. For this scope porphyrins have been grafted onto the surface of nanostructures that can provide a change of impedance as a result of the chemical interaction between porphyrinoids and volatile compounds. For instance, layers of porphyrinoids coated ZnO nanoparticles shown sensitivity towards a large spectra of compounds [5]. Exploiting the optical properties of porphyrins, the sensitivity of this sensors can be triggered by light. As a result, these devices show a negative sensitivity to electron donor compounds (e.g. amines) and a positive sensitivity respect to other compounds. This property can be fruitfully exploited in sensor arrays configuration to classify complex samples such as foods and furthermore to detect spoilage processes. Another example is provided by porphyrnoids coated silica nanoparticles. In this case, the dielectric properties of silica are exploited to develop capacitive sensors whose capacitance is modulated by the absorption of volatile compounds. These sensors retains the chemical sensitivity properties of porphyrins allowing for instance to reproduce the results of the QMB sensors in the identification of COVID-19 blood serum sample.
References
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