Which one of the following can not be detected by ELISA technique

Viroid cannot be detected by ELISA technique.
The enzyme-linked immunosorbent assay is a commonly used analytical biochemistry assay, first described by Eva Engvall and Peter Perlmann in 1971.
The assay uses a solid-phase type of enzyme immunoassay (EIA) to detect the presence of a ligand (commonly a protein) in a liquid sample using antibodies directed against the protein to be measured.
ELISA has been used as a diagnostic tool in medicine, plant pathology, and biotechnology, as well as a quality control check in various industries, but it cannot detect Viroid.