What is the best technique to measure serum insulin concentrations?

ELISA is a highly specific and sensitive technique for quantifying the concentration of specific proteins, such as insulin, in a sample. It is commonly used in clinical and research settings to measure serum insulin concentrations. X-ray crystallography, FRET (Fluorescence Resonance Energy Transfer), enzyme activity assays, and NMR (Nuclear Magnetic Resonance) are not typically used to directly measure serum insulin concentrations and are more suitable for other types of protein analysis or structural studies.