Polyacrolein microspheres covalently coupled onto solid surfaces, e.g., glass, silicon crystals, and polystyrene, have been prepared and characterized. These surfaces were synthesized by derivatization of the substrate surfaces with SiCl3(CH2)3CN or Si(OEt)3-(CH2)4NH2. The terminal nitrile groups were then reduced to primary amine groups. Polyacrolein microspheres of various diameters (0.08 and 0.4 μm) were then covalently bound in a monolayer structure to the modified surfaces. This binding of the microspheres to the derivatized surfaces is achieved via polyvalent Schiff-base bonds formed by the interaction between aldehyde groups of the microspheres and ω-primary amine groups of the modified surfaces. Residual amine groups were blocked with acetic acid N-hydroxysuccinimide ester. The residual aldehyde groups of the immobilized microspheres can then be used for covalent binding of amino ligands, e.g., proteins, in a single step and at physiological pH (or any other desired pH). The potential use of the immobilized polyacrolein microsphere surfaces for diagnostics has been demonstrated by determination of α1-antitrypsin in human serum with trypsin bound to the immobilized microspheres. The comparison between this new method for the determination of α1-antitrypsin and the routine methods is discussed.