Applying total internal reflection excitation and super critical angle fluorescence detection to a morphine assay

A surface-sensitive fluorescence measurement platform is utilised in the detection of morphine. The platform is based on a polystyrene parabolic lens that enables the simultaneous application of total internal reflection excitation and supercritical angle fluorescence detection in the measurements. The molecular recognition of morphine is based on two antibodies, one against morphine and the other against the immune complex formed between the anti-morphine antibody and a morphine molecule. The antibodies are applied in a sandwich-like format in a one-step test, where the molecular binding onto a liquid-solid-interface is monitored in real time. Morphine concentrations between 0.6 and 18.2 ng/mL were reliably determined in 60 s, while concentrations down to 2.7 ng/mL were detected already in 20 s. With appropriate recognition molecules the technique is applicable also to other drugs and small analytes.