Mycotoxin Detection Plays “Cops and Robbers”: Cyclodextrin Chemosensors as Specialized Police?

Int. J. Mol. Sci. 2008, 9, 2474-2494; DOI: 10.3390/ijms9122474 OPEN ACCESS International Journal of Molecular Sciences ISSN 1422-0067 www.mdpi.com/journal/ijms/ Review Mycotoxin Detection Plays “Cops and Robbers”: Cyclodextrin Chemosensors as Specialized Police? Pietro Cozzini 1, 2,*, Gianluigi Ingletto 1, Ratna Singh 1 and Chiara Dall’Asta 3 1 2 3 Molecular Modeling Laboratory, Department of General and Inorganic Chemistry, University of Parma, Via G.P. Usberti 17/A 43100, Parma, Italy. E-Mails: (G. I.); (R. S.) INBB, National Institute for Biostructures and Biosystems, Viale Medaglie d’oro 305, 00136 Rome, Italy Department of Organic and Industrial Chemistry, University of Parma, Via G.P. Usberti 17/A 43100, Parma, Italy. E-Mail: * Author to whom correspondence should be addressed; E-Mail: ; Tel. +39-0521-905669; Fax: +39-0521-905556 Received: 29 September 2008; in revised form: 20 November 2008 / Accepted: 3 December 2008 / Published: 5 December 2008 Abstract: As in a cops and robbers play we discover new mycotoxins and metabolites everyday and we are forced to develop new molecules quickly as chemo- or biosensors or to modify existing molecules able to recognize these new hazardous compounds. This will result in an enormous cost saving to agro-food industry through the prevention and reduction of product recalls and reduced treatment costs. Here we present a brief review of the rapid methods used to detect mycotoxins, considering usefulness and limits. Then we propose a new fast, efficient and cheap methodology, based on a combination of computer chemistry aided design and fluorescence, that can help to drive synthesis in a more efficient way. Keywords: Chemosensing; fluorescence; docking; molecular engineering. Int. J. Mol. Sci. 2008, 9 2475 1. Introduction Since improvement of “life quality” is one of the most important objectives of global research efforts, in the last decade the production–processing–distribution chain has to be carefully checked “from field to fork”, quality of life being closely linked to food quality and safety. Among the most prominent hazards for consumer health, food pollutants such as xenobiotics (e.g. mycotoxins, xenoestrogens, phytoalexins) and residues (e.g. pesticides, dioxins, polychlorinated aromatic hydrocarbons, phenils) are of serious concern for the food industry (http://www.efsa.europa.eu/EFSA/efsa_locale-1178620753812_KeyTopics.htm). In particular, in the last years there has been increasing awareness of the hazards imposed on both human and animal health by mycotoxins present in food and feed. In the last years the European Union has revised the EU legislation about mycotoxins in order to harmonize the EU Members’ national laws, to enforce new limits and to regulate a wider variety of commodities. The EU legislator emended regulations not only for food but also for feed in order to improve farm animal health [1]. The chemical diversity of mycotoxins and the wide range of matrices in which they can be found pose great challenges to analytical chemists. Therefore, a need exists for a reliable, economical and easy-to-use assay for the measurement of the mycotoxin content, especially in the raw materials for food and feed production. Moreover, the fact that mycotoxins are often found as traces leads to the need for very sensitive techniques, able to detect the toxins at ppb, or even ppt, levels [2]. Therefore, there is a real need for rapid, sensitive and inexpensive sensors for the detection of toxic compounds along the food processing chain to obtain real-time monitoring data on contamination, which may be use for food safety assessment. This will result in an enormous cost saving to agro-food industry through the prevention and reduction of product rejections. Recognition-based techniques are potential candidates to fulfill many of the above requirements, due to their general high selectivity and sensitivity. Among these methods, great efforts have been made for the development of immunochemical methods for mycotoxin detection [3, 4]. Although traditional immunoassay-based methods such as Enzyme-linked immunosorbent assays (ELISA), which allow parallel analysis of multiple samples, have been widely applied to mycotoxin detection, ELISA methods are still time-consuming and suffer from false positive and/or false negative results. With the aim of simplifying procedures and developing robust, portable analytical tools, the recent trend is to focus on immunodipsticks and immunosensors, which overcome the lengthy analysis time required by ELISA assays. 2. Bio- and chemosensing in food diagnostic: fundamentals Recognition methodologies are based on the use of a sensor, which is a receptor able to selectively bind a target compound and to affect its chemico-physical properties as a consequence of binding. The change resulting from the interaction between the target (guest) and the receptor (host) can be converted into a quantifiable signal from a transducer, which is mainly electrochemical (potentiometric, amperometric, conductimetric), optical (absorbance, fluorescence, chemiluminescence), thermal or piezoelectric devices. The receptor can be a bioactive macromolecule, such as an enzyme or an antibody (biosensors), or a supramolecular host, such as cyclodextrins, crown Int. J. Mol. Sci. 2008, 9 2476 ethers or imprinted polymers (chemosensors) the former commonly known as biosensors and the latter as chemosensors [5]. The screening devices usually applied in food diagnostic are actually immunosensing methods as they mainly involve enzyme- or antibody-based approaches [6]. So far, only few studies have reported the use of supramolecular devices for chemical recognition in food and environmental analyses. 3. Fluorescence: some base principles An adequately excited system (atoms, molecules, ions) undergoes a transition from the GES (Ground Electronic State) to an EES (Excited Electronic State). In many aromatic organic compounds, when excited by UV radiation, the transition is from the lowest vibrational level (the more populated at RT) of the GES to excited vibrational levels of the first EES. When the excitation ceases, the organic molecule releases the excess energy and returns to the GES spontaneously. This can occur in different ways. The radiative emission of radiation from an EES to the GES is called luminescence, which is divided in fluorescence and phosphorescence. Fluorescence is the most common emission in solution and phosphorescence is observable especially in the solid phase [7]. In fluorescence, the transition is “spin allowed” and occurs between singlet states. The GES and EES are “singlet states” as all the electrons have opposite spins (ΔS(total spin)=0 in both the states, ΔS=0) and the total electron spin selection rule ΔS=0 is followed. The lifetime of the EES is very short (10-4 - 10-9 sec) because the transition is allowed. In phosphorescence, the transition is “spin forbidden”, and occurs betw (...truncated)