Abstract:
The successful use of biomarker antibody detection for disease diagnosis is currently
restricted to cases where the antibody affinity and specificity of interaction with
antigen is high. Evanescent field biosensing, e.g. Surface Plasmon Resonance (SPR),
and electrochemical detection, in particular Electrochemical Impedance Spectroscopy
(EIS), have been shown viable for detection of lower affinity antibodies, based on the
principle that these technologies allow the measurement of antibody binding to
immobilized antigen, i.e. without the need to wash away excess, non-bound
antibodies or using labelled antibodies. Proof of principle for this in the case of
detection of biomarker anti-mycolic acid antibodies for TB diagnosis has been
provided in the Mycolic acid Antibody Real-Time Inhibition assay (MARTI) by our
research group. Although already patented and published, MARTI is not yet a feasible
diagnostic test due to slow sample turn-around time, affordability and technical
vulnerability associated with unstable lipid antigen surface chemistry and the
difficulty of standardization of liposome carriers of mycolic acids used for measuring
the binding inhibition of serum antibodies to immobilized antigen. Here, these
challenges were addressed by investigating the use of a magnetic field for more stable
lipid antigen immobilization, new phospholipid compositions to generate more stable
liposome carriers for lipid antigen in solution and the use of screen-printed electrodes
(SPE) in EIS to address affordability of diagnosis and improve sample turn-around
time. The latter approach appeared quite promising in distinguishing a TB positive
and a TB negative patient serum and is amenable to automation by means of a flow
injection system.
