Evanescent wave fibre optic sensor for detection of L. donovani specific antibodies in sera of kala azar patients.

An easy-to-use technique for detection of antibodies specific for the parasite L. donovani in human serum sample has been developed. The method is based on an evanescent wave generated from a tapered configuration of decladded optical fibre and does not require any volumetric measurement. Tapered fibres are immobilized with the purified cell surface protein of L. donovani by covalent bonding. Treated fibres are incubated with the patient serum for 10 min followed by incubation with goat anti human IgG tagged FITC. Fluorescent intensity from the fibre has been shown to be proportional to L. donovani specific antibodies present in the test sera. Direct readings can be obtained after signal enhancement through a photomultiplier tube within 5 min. The system, when tested on 12 positive sera, did not show any false negative result. Also, no false positive result was obtained with serum samples of patients infected with leprosy, tuberculosis, typhoid and malaria, showing the specificity of the sensor and efficacy of the technique.