**3. Synthesis methods of MIPs**

The synthesis method of MIPs can be a different type. Bulk, suspension, emulsion, precipitation, multi-step swelling, and surface imprinting were the methods which were summarized. Bulk polymerization is the common method to prepare MIPs. The bulk polymerization is rapid, simple preparation, needs no sophisticated or expensive instrumentation. But after polymerization of the bulk polymer, it has to be crushed, ground and sieved to an appropriate size. After grinding, the polymer was in irregular particles in shape and size, and also some high affinity binding sites are destroyed. Bulk polymers have a heterogeneous binding site distribution which is limited the use of MIPs in chromatography. The other techniques of preparing imprinting polymers are suspension polymerization, emulsion polymerization, seed polymerization, precipitation polymerization and surface imprinting. The more homogeneous binding site distribution can be taken by these techniques. The MIPs which is prepared by conventional suspension polymerization, where water is used as a continuous phase to form a droplet of pre-polymerization mixtures in the presence of a stabilizer or surfactant. However, the MIPs prepared by suspension polymerization is polydisperse in size (a few to a few hundred micrometers) and displayed poor recognition. The liquid perfluorocarbon or mineral oil (liquid paraffin) can be used while preparing MIPs by suspension polymerization technique to prevent poor recognition. But, liquid perfluorocarbons immiscible with almost all organic solvents (chloroform, dichloromethane, toluene), monomers and cross-linkers. The emulsion polymerization is as an effective method to produce monodispersed polymeric particles. The disadvantage of emulsion polymerization was the presence of remnants of surfactant in polymerization media. Precipitation polymerization have some advantages in synthesizing spherical particles such as free of surfactant, in one single preparative step and with excellent control over the particle size. The seed polymerization, a typical multi-step swelling and polymerization, produced monodispersed

MIPs. In this technique, the use of water was weakened recognition. In addition, the multistep procedure is very time-consuming. Surface imprinting is another technique nowadays using MIPs mostly synthesized. The biggest problem of MIP was bleaching of template molecule due to the high cross-linking nature of MIPs, which will result in incomplete template removal, and slow mass transfer. Fortunately, this problem can be resolved by surface imprinting, in which the imprinted templates are situated at the surface of the material's surface. Compared to traditional MIPs, surface imprinted polymers possess not only higher binding capacity but also faster mass transfer and binding kinetics. Many particles have been used for the surface imprinting process, such as activated silica, Fe3O4 (magnetic) nanoparticles, chitosan, activated polystyrene beads, quantum dots (QDs) and alumina membranes. The magnetic separation is an effective technique for separation of complicated samples. The magnetic nanoparticles have an advantage of its fast recovery, high efficiency, low cost, and direct purification from a mixture without any pretreatment. In recent years, magnetic MIPs have become a hotspot based on the significant advantages of magnetic separation over conventional methods. Generally, preparation of MIPs-coated magnetic nanoparticles (MNPs) involves three steps: (1) preparation of Fe3O4 MNPs; (2) surface modification of Fe3O4 MNP with TEOS, oleic acid, ethylene glycol or poly (vinyl alcohol) and (3) synthesis of surface imprinted MNPs using a sol–gel process or free radical polymerization [16–18].
