Porphyrin Supramolecular Aggregates and Chemical Sensors: A Marriage for Smart Devices

The development of smart and reliable chemical sensors has become increasingly important for several application fields, ranging from medical to environmental  applications. A chemical sensor is in fact a device that transforms chemical information, ranging from the concentration of a specific sample component to the total composition analysis, into an analytically useful signal. Porphyrins are useful materials for chemical sensors development, since in these devices the porphyrins play the role of receptor, the component that interacts with the chemical environment and for this reason it mostly influences the performances of the device. Since 1995 we have been involved in the preparation of different kind of porphyrin based chemical sensors, for the detection of analytes both in liquid and in the gaseous phase.¹ A critical step in the development of such a devices is the deposition of porphyrins as solid layer, because in this process it is necessary from one side to preserve the recognition properties of the single molecules and from the other side take eventually advantage of the additional interaction pathways that the supramolecular organization can offer.² This latter feature could be furtherly improved by the development of hybrid sensing materials, where the recognition properties of porphyrin aggregates are boosted by the coupling with both inorganic or organic substrates.

We have been interested in this approach, developing hybrid materials where porphyrins have been deposited onto ZnO nanorods.³ More recently we have also exploited a simple non-covalent approach to prepare chiral aggregates of poly-lysine, deposited onto a quartz crystal microbalance surface and then used  these films as a matrix to form a supramolecular complex with a negatively charged porphyrin, the tetrasulfonatophenylporphyrin (TPPS). This study aims to develop chemical sensors able to perform enantioselective recognition, by functionalization of quartz crystal microbalances (QCM) with chiral supramolecular aggregates. Chemical sensors able to perform rapid and reliable chiral discrimination have an enormous importance for all the fields where the discrimination of enantiomeric pairs is a mandatory task, such as for example drug industry. For this reason the preparation of chiral films is a necessary step, to develop reliable chemical sensors for enantioselective recognition. In this scenario the non-covalent approach can represent a simple way to obtain sensing films featuring chiral properties. We tested the chiral recognition performances of different QCM functionalized with poly-lisine-TPPS films, exposing them to the vapors of some volatile chiral compounds. We studied also in detail the experimental parameters influencing the sensor responses.

In the present work we summarise our recent results, showing a promising route for chemical sensors applications.

References

 

1. R. Paolesse, D. Monti, S. Nardis, C. Di Natale, in Handbook of Porphyrin Science, eds. K. M. Kadish, K. M. Smith, R. Guilard, World Scientific, Singapore, 2011, Vol. 12, p. 121.

2. R. Paolesse, D. Monti, C. Di Natale, Mater. Today,

2010, 13, 46.

3. Sivalingam Y., Martinelli E., Catini A., Magna G., Pomarico G., Basoli F., Paolesse R., Di Natale C., J. Phys. Chem. C., 2012, 116, 9151.