## 2 Molecular Imprinting Process  
As reported above, molecular imprinting is a technique to synthesize highly cross-linked polymers capable of selective molecular recognition. The principle is summarized in Figure 1: polymerization of a monomer occurs in the presence of the target molecule (template) which is incorporate in the polymer matrix. The process starts with dissolution of template, functional monomer, cross-linking agent and initiator in a porogenic solvent. Functional monomers are chosen to interact with the template molecule since the formation of a stable template-monomer complex is fundamental for the success of molecular recogntion. Monomers are positioned spatially around the template and the position is fixed by copolymerization with cross-linking monomers. The polymer obtained is a macroporous matrix possessing microcavities with a three-dimensional structure complementary to that of the template. Thus, the removal of the template molecules from the polymer, by washing with solvent, leaves binding sites that are complementary in shape to the template. Consequently, the resultant polymer recognizes and binds selectively the template molecules. The binding sites show different characteristics, depending on the interactions established during the polymerization. Traditionally, molecular imprinting is classified according to the nature of the interactions between monomer and template during the polymerization. For their insoluble nature, MIPs are notoriously difficult to characterize. However, some analytical techniques can be utilized for their chemical and morphological characterization, including solid-state NMR techniques [30], elemental micro-analysis and Fourier-Transform Infrared Spectroscopy (FT-IR) [31] which can be applied to obtain chemical information on the composition of the polymer. CP-MAS (cross polarization magic angle spinning) NMR spectra for MIP characterization have been reported in a few works even if solid state NMR is a useful method to determine chemical composition of insoluble polymers. For instance, [PERSON] and co-workers [30] very recently confirmed the incorporation of crosslinking agent EgDMA and functional monomer 4-vynilpyridine in the polymer backbone of the prepared MIP by \({}^{13}\)C CP-MAS-NMR. More often FT-IR studies have been used for MIPs characterization through the evaluation of functional groups incorporation in the polymer and through the comparison between polymer and functional monomer spectra to follow the decreasing or disappearance of some signals, such as carbon double bond stretching of a vinyl functional monomer, as a result of polymerization of the polymerizable group of the monomer [31]. Morphological characteristics of MIPs can be properly investigated by microscopy techniques, such as light microscopy to verify the natural integrity of polymer beads and scanning electron microscopy (SEM) to image polymer macro-pores [31, 32]. Moreover, nitrogen sorption porosimetry by using BET (Brunauer, Emmett and Teller) analysis is the main technique used to determine specific surface area, specific pore volume, pore size distribution and average pore diameter values of the polymer particles while mercury intrusion porosimetry is sometimes used and is more suitable for larger pores characterization. However, a very important level of characterization for MIPs concerns the molecular recognition behavior, such as the binding capacity, and one of the best methods for evaluating binding capacity and selectivity is the batch rebinding. MIPs can also be used directly as chromatographic stationary phases which generally provide a quicker and easier method for analyzing the binding properties of MIPs [22, 32, 33]. Scatchard analysis is a common model to evaluate the binding behavior of MIPs in batch rebinding experiments.