Sorting out molecules reacting with acetylcholinesterase by enzyme encapsulation in liposome

Enzymes are considered as providential molecules for biosensor design because of their sensitivity and the high specificity of the reactions they catalyse. However, their active sites often display low selectivity, a lot of molecules may enter and interfere with catalysis. These molecules may be either competitive inhibitors, activators or molecules which change the physico-chemical environment of the enzyme (pH, ionic strength). They produce the "matrix effect" that lowers the reliability of biosensors. We show here that encapsulation of enzymes in liposomes inserts a barrier between the enzyme and the external environment and protects the enzyme in a stable nano-environment for an optimal activity. This barrier sorts out the molecules that could react with the enzyme according to their hydrophobicity. Acetylcholinesterase is used to detect organophosphorous and carbamate insecticide residues but several molecules (reversible inhibitors, pH and ionic strength modifiers) generate matrix effects in free conditions. These perturbations were completely ineffective following enzyme encapsulation. (C) 2004 Elsevier B.V. All rights reserved.