Preparation of unsymmetrical microspheres at the interfaces

Many synthetic microspheres are spherical and symmetrical because of the th ermodynamical limitations of the reaction systems. We developed modificatio n techniques to prepare spherical microspheres with intrinsic unsymmetry, f or example, a microsphere with both an anionic and a cationic part. The mod ification was performed at the liquid-solid interface. Reactive microsphere s with p-nitrophenyl moieties were settled onto the IgG-preadsorbed substra te, and the reaction between the activated ester moieties and Ige molecules proceeded only at the interface upon attachment. After the reaction, the m odified microspheres were detached from the substrate with ultrasonication. In another modification at the air-water interface, the dispersion of reac tive microspheres in ethanol was first spread on a water surface to produce the monolayer of microspheres, and then hydrolysis at the water side of th e monolayer was performed by adding a NaOH aqueous solution to the subphase . After this unsymmetrical hydrolysis, we carried out IgG immobilization wi th the remaining reactive moieties. Tn both interface methods, the immobili zed IgG molecules were labeled with colloidal gold particles conjugated wit h anti-IgG antibodies. Transmission electron microscopy indicated that gold particles could be observed on only the immobilized side. Small microspher es were coupled to the reactive microsphere, and its unsymmetry was confirm ed by scanning electron microscopy. Such unsymmetrical microspheres will be applicable to the electrical rheology, diagnosis, display technology, and creation of functional devices through the assembling of microspheres.