## 5 Molecular Imprinting by Sol-Gel Derived Techniques  
The interest in materials obtained by sol-gel method has grown considerably in recent years, as evidenced by the multitude of published papers. The materials obtained by this method can be used in different applications, including chemical sensors and biosensors, coatings and catalysts [132]. Overall, the sol-gel process implies several actions such as activation of precursor (usually involves hydrolysis), polycondensation, gelation, aging, washing, drying and stabilization [133; 134]. The sol-gel process involves the transition from liquid state to a \"sol\" and then into a \"gel\" network structure [135]. In this respect, metal alkoxides undergo hydrolysisin aqueous media toothain hydroxyl groups. The next step involves \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Synthesis Method** & **Receptor** & **Support** & **Analyte** & **Characterization** & **LOD** & **Refs.** \\ \hline Drop coating & MIP film & SPCE 1  & Serratline & CV 2  & CV 2  & 1.99 \(\times\) 10\({}^{-9}\) M & [117] \\ Coating & MIP film & Paper-based device & deoxyguanosine and 3-nitrotyrosine & CV and SWV 4 & 1.38 \(\times\) 10\({}^{-8}\) M & [118] \\ Dropcasting & MIP film & SPCE & 3-nitrotyrosine & & and 2.7 \(\times\) 10\({}^{-9}\) M & [118] \\ Dropcasting & Membrane & SPCE & Disphenol A & CV and HPLC 5 & 6.0 \(\times\) 10\({}^{-11}\) M & [119] \\ Dropcasting & Membrane & Proper used as electrode & & Potentiometric detection & 1.5 \(\times\) 10\({}^{-7}\) M & [120] \\ Spincoating & MIP & GCE 6  & Phenylphrine & DPV and HPLC & - & [124] \\ Spincoating & MIP film & Au electrode quartz crystal & Chloramphenicol & Oscillation frequency & 7 \(\times\) 10\({}^{-8}\) ug\(\cdot\)mL\({}^{-1}\) & [125] \\ Spincoating & MIP film & Quartz plates & 1-hydroxyprene & CV & 3.353 \(\times\) 10\({}^{-10}\) M & [126] \\ Dropping & Film & SPCE & Trazosin & CV, DPV and EIS 7 & 3.0 \(\times\) 10\({}^{-7}\) M & [129] \\ Dropcasting & Film & GCE & Diphenylamine & DPV & 5.0 \(\times\) 10\({}^{-8}\) M & [130] \\ Functionalization of carbon black paste electrode & Layer & Functionalized Carbon black & Imazehapyr & DPV & 3.0 \(\times\) 10\({}^{-8}\) M & [131] \\ \hline \hline \end{tabular}  
* 1 SPCE: screen-printed carbon electrode; 2 : CV: cyclic voltammetry; 3 : DPV: differential pulse voltammetry; 4 : SWV: square wave voltammetry; 5 : HPLC: high performance liquid chromatography; 6 : GCE: glassy carbon electrode; 7 : EIS: electrochemical impedance spectroscopy.  
\end{table} 
Table 3: MIP-based sensors obtained using MIP particles embedded in pastes or inks. the obtaining of a 3D network by the formation of Si-O-Si bonds resulting from the polycondensation reaction of hydroxyl groups and remaining alkoxyl groups. The reaction can be performed under basic or acidic conditions depending on the morphology of the material that is required. The porosity and the morphology of the sol-gel materials depend on several parameters, i.e., the solvents, the pH, drying process, reaction conditions and catalysts. These aspects are very important because, given the porosity and morphology, the obtained materials can be used for different applications [133; 136; 137; 138]. This synthesis method presents multiple advantages, namely mild synthesis conditions (for example, the synthesis can be performed at room temperature), the obtained materials possess good optical properties, high thermal stability and high porosity, which can be corelated with a high surface area [139; 140; 141]. The sol-gel materials can be prepared in different forms, including thin films (for sensors and coatings) [14; 142; 143; 14], composites (such as alumina reinforced materials), particles (for solid-phase extraction or for incorporation in thin films for sensor development) [138]. By combining the sol-gel method with molecular imprinting, performant sensitive layers can be obtained for sensor development (Figure 6). The sol-gel MIP films can be prepared by the drop coating or spin coating method and also by electrodeposition [144; 145].