Polypeptide linker and method of analyzing target material using the same

A method of detecting a target material in a sample, the method comprising:

• (a) incubating a sample with
• (i) an antibody that binds to a target material in the sample, wherein the antibody comprises an Fc region, and
• (ii) a polypeptide linker comprising an Fc-binding region and an enzyme cleavage region, wherein a microparticle is coupled to the polypeptide linker, to form a complex;
• (b) isolating the complex based on the physical or chemical properties of the microparticle;
• (c) incubating the complex with an enzyme that recognizes the enzyme cleavage region to cut the polypeptide linker at the enzyme cleavage region, which results in separation of the microparticle from the complex;
• and
• (d) detecting the complex without the microparticle, thereby detecting the target material in the sample.