Correct option is (d) Immunosensor
Explanation: Principle of Immunosensor is represented in the diagram. ELISA is performed initially and then the following steps are followed:
• A transducer is coated with immobilized antibody. The transducer is immersed in a solution containing a mixture of a known amount of antigen-enzyme conjugate plus the unknown concentration of sample antigen.
• After a suitable period, the antigen and antigen-enzyme conjugate will be distributed between the bound and free states dependent upon their relative concentrations.
• Unbound material is washed off and discarded. The amount of antigen-enzyme conjugate bound is determined directly from the transduced signal.