A capture device for capturing a biological substance can include: a substrate; a graphene-oxide layer on the substrate; at least one polydopamine polymer coupled with the graphene-oxide; and at least one targeting receptor coupled to the polydopamine(s), wherein the targeting receptor is capable of targeting/binding with a target biological substance. The graphene-oxide may be covalently coupled with the substrate and polydopamine, and the polydopamine may be covalently coupled with the targeting receptor. The targeting receptor can be an antibody or fragment thereof. The target biological substance can be an exosome. The substrate can be a particle (e.g., magnetic, such as magnetically responsive) or a surface in a microfluidic channel. The surface can be a top surface of a post, the post having a Y-shaped cross-sectional profile. In one aspect, the substrate is a particle. The capture device can include the target biological substance bound to the targeting receptor.