This invention relates to a surface coating for capture circulating rare cells, comprising a nonfouling composition to prevent the binding of non-specific cells and adsorption of serum components; a bioactive composition for binding the biological substance, such as circulating tumor cells; with or without a linker composition that binds the nonfouling and bioactive compositions. The invention also provide a surface coating for capture and purification of a biological substance, comprising a releasable composition to release the non-specific cells and other serum components; a bioactive composition for binding the biological substance, such as circulating tumor cells; with or without a linker composition that binds the releasable and bioactive compositions. The present invention also discloses a novel microfluidic chip, with specific patterned microstructures to create a flow disturbance and increase the capture rate of the biological substance.