Final answer:
The true statement about ELISAs is that they can be used to detect either antibodies or antigens. This technique allows for sensitive quantitative and qualitative analyses and does not always require a fluorescent label, large amounts of sample, or membrane filters. The correct option is D) They can be used to detect antibody or antigen.
Step-by-step explanation:
The statement that is TRUE regarding enzyme-linked immunosorbent assays (ELISAs) is D) They can be used to detect antibodies or antigens. ELISAs involve attaching either antigens or antibodies to the wells of a microtiter plate, which allows for the subsequent detection of specific antibodies or antigens present in a sample using enzyme-conjugated antibodies and a subsequent colorimetric or fluorogenic reaction. This technique is highly sensitive and allows for both qualitative and quantitative analysis.
While it's true that some forms of ELISA can use a fluorescent molecule as a label (immunofluorescence assays), it is not necessarily part of the basic definition or functionality of an ELISA, hence option A is not exclusively true. ELISAs are quantitative, which disproves option B. They do not require large amounts of serum, so option C is incorrect. Lastly, ELISAs do not necessarily involve the use of membrane filters, which makes option E incorrect. The correct option is D) They can be used to detect antibodies or antigens.