Liquid crystals decorated with linear oligopeptide FLAG for applications in immunobiosensors

Immunobiosensors are emerging as powerful tools for diagnostic applications. In this paper, we exploit optical properties of liquid crystal (LC) and the specific epitope-antibody interaction to develop an optical immunobiosensor which can be used to detect monoclonal anti-FLAG M2, a model antibody. The sensitive layer of this immunobiosensor is a monolayer of immobilized oligopeptide CDYKDDDDK (FLAG) at an LC/aqueous interface. The linear oligopeptide can function as an epitope which can be recognized by anti-FLAG M2. When the LC is modified with 50 μM of FLAG and then exposed to an aqueous solution containing anti-FLAG, anti-FLAG binds to the immobilized FLAG epitope and triggers orientational transition of LC. Because of the optical birefringence of the LC, the orientational transition is accompanied by changes in the optical images of LC from dark to bright under crossed polarizers. The detection limit for the system is 27 ng/mL of anti-FLAG, and the response time is < 1 h. The binding of anti-FLAG to its motif FLAG oligopeptide is also very specific. When a variant epitope CDAKDDDDK is used, no apparent optical response can be observed after the addition of anti-FLAG.