Qbeads-Carboxyl is magnetic bead with surface functional group -COOH. The magnetic bead consists of a single-crystal Fe₃O₄ sphere core and dextran coating layer. Through chemical modification of dextran, the carboxyl groups (-COOH) are joined to the magnetic beads through a short hydrophilic linker. The hydrophilic surface ensures the magnetic beads excellent dispersion ability and easy handling property in a wide variety of buffers.

Through activation of Qbeads-Carboxyl with EDC, the ligands could be conjugated to the magnetic beads through primary amine groups such as antibody, protein, or peptide.