Due to their increasing use in agriculture, the presence of pesticides residues in food and water currently represents one of the major issues for the food safety.
Organophosphate (OP) and carbamate (CB) species are the most used pesticides at worldwide, these compounds are highly toxic due to their inhibitory effect on Acetylcholinesterase (AChE), the key enzyme for the nerve transmission: the inhibition of this enzyme leads to muscle weakness, miosis, respiratory failure, unconsciousness, convulsion and, eventually, death. For these reasons, there is a general concern on pesticide food contamination and, consequently, the development of simple and sensitive strategies for detecting toxic compounds is critically important in order to carry out the measurement “in situ” using miniaturized, cost-effective and easy to use the analytical system.
In this context, the use of biosensors can represent a powerful alternative for monitoring of pesticides in food samples because of their specificity, high sensitivity, short response time, simple operation and rapidity of use. Biosensors are based on the intimate contact between a biological element (nucleic acid, enzyme, antibody, receptor, tissue cell) and a transducer system. The biological component interacts specifically with the target analyte while the transducer transforms the signal resulting from the analyte’s interaction with the biological element into a signal that can be measured and quantified.
The biosensors based on AChE inhibition are reliable tools for the detection of organophosphate and carbamate compounds: these pesticides are able to form a link with the active site of the enzyme. The most common biosensors developed for pesticides detection are based on the inhibition of AChE enzymatic activity caused by the making of a link with the active site of the enzyme. In particular, the enzymatic activity is measured before and after the exposure to pesticide compound by different transduction techniques (such as amperometric, piezoelectric and optical transducers), through a time – consuming analysis.
The Electrochemical Impedance Spectroscopy (EIS) is an interesting transduction technology which enables the direct analyte detection by studying the electrical properties of the sensing device interface: the EIS measurements involve the analysis of impedimetric changes, at the electrode interface when a biological or chemical element interacts with the electrode surface functionalized with a bioreceptor. This type of transduction allows the development of affinity-binding biosensors with noteworthy advantages due to their direct and label-free detection for the analyte of interest.
Exploiting the inhibition mechanism of pesticides versus AChE, and the capability of EIS to measure the interaction between the analyte and the bioreceptor, we considered applying the EIS as transduction method for the novel AChE-based biosensors for the direct measurement of pesticides inhibition compounds in the real matrix.
The new label-free impedimetric affinity sensors developed based on AChE was able to detect very low pesticides concentration in particular 2,5 and 10 ug/kg for OP and CB respectively but in contrast to the most common biosensors developed for pesticides detection, based on AChE that require long time of analysis our impedimetric affinity biosensor require only 4 min excluding the incubation time.
Finally, the developed affinity AChE biosensor, with its high number of attractive characteristics associated with the use of EIS transduction can be considered as a promising candidate for pesticide detection on-site applications.
The work is led by Prof. Donatella Albanese and her Ph.D. student Francesca Malvano at the University of Salerno. A New Label-Free Impedimetric Affinity Sensor Based on Cholinesterases for Detection of Organophosphorous and Carbamic Pesticides in Food Samples: Impedimetric Versus Amperometric Detection was recently published in the journal Food and Bioprocess Technology.