Real-time recognition of Mycobacterium tuberculosis and lipoarabinomannan using the quartz crystal microbalance

A quartz crystal microbalance (QCM) immunosensor has been successfully employed to screen for both whole Mycobacteria tuberculosis (Mtb) bacilli and a Mtb surface antigen, lipoarabinomannan (LAM). One of the most abundant components of the Mtb cell surface, LAM, may be detected without the presence of the entire bacterium. Using available antibodies with proven utility in enzyme-linked immunoassays (ELISAs), a sensor was designed to measure Mtb bacilli and LAM. Equilibrium association constants (Ka) were determined for the interaction of Mtb with immobilized α-LAM and anti-H37Rv antibodies, where avidity was seen to strengthen this interaction and provide for greater binding than might have otherwise been achieved. The binding of LAM to immobilized α-LAM had a high associate rate constant (ka) allowing for rapid detection. Evaluating these binding constants helped to compare the sensitivity of these immunosensors to conventional ELISAs. The use of these assays with better antibodies may allow for immunosensor use in determining LAM as a point-of-care (POC) diagnostic for Mtb.