Au-labeled antibodies to enhance the sensitivity of a refractometric immunoassay: detection of cocaine.

An integrated platform for a very sensitive detection of cocaine based on a refractometric biosensor is demonstrated. The system uses a waveguide grating biosensor functionalized with a cocaine multivalent antigen-carrier protein conjugate. The immunoassay scheme consists of the competitive binding of cocaine-specific antibodies to the immobilized conjugates. A 1000-fold enhancement of the sensor's sensitivity is achieved when using gold conjugated monoclonal antibodies instead of free antibodies. Together with the optimization of the assay conditions, the setup is designed for a quick identification of narcotics using automated sampling. The results show that the presence of cocaine in a liquid sample could be identified down to a concentration of 0.7 nM within one minute. This value can be reduced even further when longer binding time is allowed (0.2 nM after 15 min). Application of the system to detection of narcotics at airport security control points is discussed. Copyright Â