The optical density was seen to linearly increase with the concentration of mAb (Fig. 3a) . ELISA carried out for the conjugate showed the binding of the conjugated antibody to the coated RANK receptor. The sCT attached to the conjugate was detected using an anti-calcitonin antibody, thus confirming the intactness of mAb-sCT conjugates. Optical density for mAb alone was negligible, as it did not have calcitonin to be detected by anti-calcitonin antibody. Similarly, OD for sCT-PEG was also significantly low, as it did not have the anti-RANK mAb targeting moiety necessary to bind to the RANK coated plate (Fig. 3b) . ELISA-derived spectrophotometric absorbance values for mAb, sCT-PEG and mAb-sCT conjugate were 0.002, 0.025 and 0.153, respectively.