# A Review: Using Multiple Templates for Molecular Imprinted Polymer: Is It Good?
## 1 Introduction  
Molecularly imprinted polymer (MIP) has selective binding sites in the form of cavities or pores formed due to template removal through an extraction process after polymer formation. The function of the selective binding sites is to identify target molecules with the same sizes, shapes, structures, and properties as the template [1, 2]. MIPs have numerous advantages, including high selectivity, affinity, and physical and chemical stability, ease of preparation, low costs, and resistance to harsh environmental conditions [3]. As a result, molecular imprinting has received a lot of attention and is now widely used for a variety of target molecules, including chemicals and drugs. MIP components comprise a template, a functional monomer, a crosslinker, a solvent (called porogen), and an initiator. These components have an important role in the process of forming the MIP [4]. Molecular detection in MIPs depends on the interaction between the template and the functional monomer by the formation of a suitable cavity. The functional monomers must be able to provide suitable functional groups to form a stable complex with the template [5]. The monomers commonly used are methacrylic acid (MAA), acrylamide (AM), 4-vinylpyridine (4-VP), and itaconic acid [6]. In the process of preparing a MIP, the crosslinker fixes the functional monomer bonds around the template so that the rigid structure of the MIP remains unchanged after template removal. In other words, the crosslinker functions as an adhesive/glue to secure the polymer's shape and maintainits stability [7]. Commonly used crosslinkers are dicumyl peroxide, triallyl isocyanurate, \(N\),\(N\)-methylenediacrylamide, ethylene glycol dimethacrylate (EGDMA), tetraethoxysilane, and diphenyldiethoxysilane [6]. The solvent used is generally called a porogen (pore generator) and also acts as a dispersion agent [4]. Commonly used solvents are chloroform, acetonitrile, \(N\),\(N\)-dimethylformamide (DMF), dichloroethane, methanol, tetrahydrofuran (THF), 2-methoxyethanol, and toluene [6]. The formation of MIPs by the free radical polymerisation method requires a free radical source. In this case, an initiator is used as a source of free radicals [4]. Commonly used initiators are azobis (nitriles) and peroxides [6]. Figure 1 provides an illustration of how MIPs are synthesised. In the vast majority of cases, the molecule chosen as the template is the one that must be extracted by the MIP, ensuring optimal recognition during the extraction process [5]. In addition, there are other factors to consider when choosing a template, such as selecting a template with a low cost, a large molecular volume so that it is not easy to enter or exit the MIP's moulding cavity, and thermal stability [8]. A single template molecule is commonly used to create a MIP that is highly selective for a target analyte [9; 10]. Table 1 provides a summary of templates that have been used to generate single-template MIPs (ST-MIPs). Although ST-MIP has good selectivity and sensitivity, it is less effective when applied to the isolation or analysis of more than one compound. This is because new MIP synthesis is required for each different compound. However, for practical purposes, imprinting procedures are not limited to a single template [11]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Template Type** & **Template** & **Polymerisation Method** & **Application** & **Reference** \\ \hline \multirow{8}{*}{Drugs} & Valsartan & Bulk polymerisation & SPE & [12] \\ \cline{2-5}  & \multirow{4}{*}{Ofloxacin} & Surface-initiated atom & & \\  & & transfer radical & SPE & [13] \\ \cline{1-1}  & & polymerisation & & \\ \cline{1-1}  & & & Not mentioned, but it can be & \\ \cline{1-1}  & \multirow{2}{*}{Dexamethasone} & Surface imprinting & & utilised in any application & \\ \cline{1-1}  & & polymerisation & & where a sorbent is required to & \\ \cline{1-1}  & & polymerisation & & purify and concentrate a & \\ \cline{1-1}  & & & target analyte & \\ \hline \hline \end{tabular}
\end{table}