Sensors and Actuators B 47 (1998) 70–76 Self-assembled monolayers of mercaptoporphyrins as sensing material for quartz crystal microbalance chemical sensors Roberto Paolesse a, *, Corrado Di Natale b , Antonella Macagnano b , Fabrizio Davide b , Tristano Boschi a , Arnaldo D’Amico b a Dipartimento di Scienze e Tecnologie Chimiche, Uniersita ` di Roma ‘Tor Vergata’, Via della Ricerca Scientifica, 00133 Rome, Italy b Dipartimento di Ingegneria Elettronica Uniersita ` di Roma ‘Tor Vergata’, 00173 Roma, Italy Abstract Thiol-functionalized metalloporphyrin have been deposited as self-assembled monolayers onto the gold pad of quartz crystal microbalances (QMBs). The sensitivities of the resulting sensors have been measured with respect to model volatile organic compounds (VOCs), interesting for future practical applications. The sensitivities of these functionalized QMBs depend on the number of the sulfide groups present at the peripheral positions of the porphyrins, but they are higher if compared with the corresponding casting coated sensors. © 1998 Elsevier Science S.A. All rights reserved. Keywords: Porphyrins; Self-assembled monolayers; Quartz crystal microbalance; Gas sensors 1. Introduction The development of chemical sensors for compounds detection in the gaseous state has been object of several investigations [1]. This great interest can be explicate by the numerous and fruitful applications of these devices, ranging from the environmental control to food analysis. From a schematic point of view, a chemical sensor is constituted by both a sensing material, interacting with the species present in the environment and a transducer which converts these chemical informations in some measurable data [2]. While a large number of different transducers has been developed, due to the continuous technological progress, a critical point for the development of a chemical sensor is the choice of the sensing material. A flurry of different classes of molecules have been pro- posed during these studies, able to bind volatile organic compounds (VOCs) by means of different types of interactions, such as electrostatic, coordination, hydro- gen bonding, etc.. The first attempt was to design molecules with high selectivity, i.e. able to bind a single compound of a complex mixture. The overwhelming complexity of the chemical composition of the analyzed environments lead to the development of a different approach, where the analysis is carried out with an array of different sensors, each of them having different properties of selectivity towards the chemical species present in the mixture. In this way all the sensors give an information related to the whole environment and the subsequent data analysis interprets these informa- tions related to the chemical environments. Due to the analogies with the mammalian olfact, this approach of chemical sensing has been called electronic nose procedure. In the last few years the authors have been interested in the development of a sensor array composed by quartz crystal microbalances (QMB) coated with metal complexes of porphyrins for the analysis of VOCs [3–6]. The choice of metalloporphyrins as sensing material for these sensors was particularly significant: in fact they are able to bind in a reversible way a large number of chemical compounds, so mimicking their biological ac- tivity, for example in the hemoglobin [7], furthermore they are stable compounds and can be stored and used without strong precautions. Porphyrins are probably the most versatile ligands and almost all metals present in the Periodic Table have been coordinated to this macro- cycle: this feature allows the preparation of a wide range of different sensors with the same porphyrin, by chang- ing the metal coordinated. * Corresponding author. Tel.: +39 6 72594386; fax: +39 6 72594328; e-mail: paolesse@tovvx1.ccd.utovrm.it 0925-4005/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved. PII S09 2 5 -4 005(98)0005 2- 5