Which technique is widely used to quantify a specific protein using antibodies in solution?

• A. Western blot
• B. ELISA
• C. Mass spectrometry
• D. Immunohistochemistry

Answer: (B)

Quantifying a specific protein in a liquid sample with antibodies relies on an immunoassay that converts antigen–antibody binding into a measurable signal. ELISA is the standout method here because it is built to detect and quantify proteins directly in solution and to produce a signal that scales with the amount of target present.

In an ELISA, the target protein from the liquid sample binds to antibodies arranged on a plate, and a second antibody linked to an enzyme generates a colorimetric or fluorescent readout. The intensity of that signal is proportional to the protein concentration, giving a precise quantitative result. This format is highly sensitive, has a wide dynamic range, and can be scaled to many samples, which is why ELISA is the go-to choice for quantifying a specific protein in solution.

Western blot also uses antibodies, but it involves separating proteins by gel electrophoresis and transferring them to a membrane, which is more about identifying presence and approximate amounts rather than straightforward, high-throughput quantification in solution. Mass spectrometry can quantify proteins without antibodies, and immunohistochemistry detects proteins in tissue sections rather than in liquid samples, making them less suitable for simple quantification in solution.