This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Radiology
Radioisotopes are used in the following technique except – 
Select and explain. 
A. Mass spectroscopy, B. RIA, C. ELISA, D. Sequencing of nucleic acid
C: ELISA
Answer: C: ELISA 
Explanation: ELISA (Enzyme linked Immunoabsorbent Assay) is an enzyme-based immunoassay and does not use radioactive isotopes. A test similar to ELISA which uses radioactive isotope in place of the enzyme is known as Radioimmunoassay (RIA). Nucleic acid sequencing, mass spectroscopy & RIA are tested using radioisotopes.