Immunosensors based on supported lipid membranes, protein films and liposomes modified by antibodies

The comparison of physical properties, sensitivity and reproducibility of various detection parameters of several newly developed affinity biosensors for determination of human IgE and herbicide 2,4-D is presented. The protein film based biosensors were composed of antibody (swine anti-human IgE (Q-SwaHU/IgE) or monoclonal antibody (MAb) against herbicide 2,4-D) attached to thin gold support through cysteamine or cysteamine-bovine serum albumin. The antigen (Ag)-antibody (Ab) interaction was detected by measurement of conductivity. The detection limit for human IgE was similar to 1 nM, however, the sign of response depends on the method of antibody attachment to the gold support. This type of design and detection method was not appropriate for detecting small molecules, like 2,4-D. In the case of metal (stainless steel or gold) supported lipid films (s-BLM), the sensor was constructed by means of binding of avidin-modified antibody to s-BLM contained biotinylated phospholipids. Measurement of electrical capacitance, C, and elasticity modulus in direction perpendicular to the membrane plane, E-perpendicular to, allowed to detect the Ag-Ab reaction, that resulted in decrease of C and increase of E-perpendicular to. Most reproducible results have been obtained with lipid films supported on thin gold layers with detection limit of determination of 2,4-D similar to 1 mu M. The best reproducibility and sensitivity (0.1-1 nM) have been obtained in liposome immunoassay. The Ag-Ab reaction was monitored by means of measurement the changes of ultrasound velocity in liposome suspension. (C) 1999 Elsevier Science S.A. All rights reserved.