## 5 Molecular Imprinting by Sol-Gel Derived Techniques
The electrochemical behavior of the sensors was tested by different methods (CV, EIS, DPV), out of which DPV technique revealed a detection limit of \(10^{-7}\) M for europium [152]. [PERSON] and his team [153] developed a sol-gel MIP-based sensor for aspartic acid recognition. The MIP precursor solution was prepared by dissolving PEG (Polyethyleneglycol) in ethanol and, after stirring the template molecule [(L-Asp)Cu\({}_{2+}\)(NC-L-Asp)] was added. Finally, TEOS was added to this solution, at reflux, and the films were cast in double layer, by dripping the solution on the GCE surface. In this case, a limit of detection of 1.77 uM was achieved by SWSV (square-wave stripping voltammetry) [153]. Studies on the effects on human health for the use of aristolochic acid have led to a link between its presences and liver cancer. Therefore, [PERSON] and her co-workers [156] developed a sensor based on an MIP, using the sol-gel technique, for aristolochic acid detection. In this respect, they prepared a precursor solution containing the template and the monomer (PTMOS) and kept it in the refrigerator, after which magnetic carbon nanotubes (MCNTs), previously functionalized with carboxyl groups, crosslinker (TEOS) and the catalyst were added. The modified MIP-MCNTs were extracted from the solution with a magnet and tested in rebinding experiments. The imprinting factor of MIP particles was 3.17, with the detection limit 0.034 ug/mg [154]. Other concerning compounds that may affect human health are insecticides. For example, trichloron can cause memory problems, depression, disorientation, etc. Thus, [PERSON] and co-workers [155], proposed an electrochemical sensor for its detection. The MIP film was synthesized by a sol-gel method in acidic condition, which involved the use of TEOS, PTMOS, MTMOS and the template (trichloron). The authors used a GCE as support for the MIP film deposition, which was performed by immersing the electrode in the previously prepared precursor solution. The films were analyzed by different electrochemical technique, i.e., EIS, CV and presented good sensitivity and selectivity, with a LOD of 2.8 \(\times\) 10\({}^{-9}\) g/mL [155]. In the next part of this section hybrid methods for sol-gel MIP films synthesis are presented. In this respect, many studies were found for MIP film synthesis by combining the sol-gel method with electropolymerization (according to the procedure sketched in Figure 6). In this case, the MIP solutions are prepared by sol-gel methods, whereas the deposition on the electrode surface is carried out by electropolymerization. Recently, [PERSON] and co-workers [156] developed a sensor for clenbuterol detection. Clenbuterol is used as veterinary medication. At the same time, if identified in human samples (athletes), it may be corroborated with doping. Therefore, in this study, a three-electrode system was used for sensor development and the imprinted films were deposited on the gold electrode surface. To this end, a sol-gel solution was prepared by dissolving the monomer (APTES), the crosslinker (TEOS), the template (clenbuterol) and KCl in ethanol, followed by electrochemical deposition at \(-\)0.8 V for 30 min. The prepared films were characterized by various techniques, from which DPV revealed a good value for the LOD of 31 nM [156]. The group of [PERSON] [157] proposed an electrochemical sensor based on MIP for melamine detection. The MIP solution was prepared by dissolving TEOS, PTMOS, MTMOS and melamine in ethanol/water/HCI, in which the GCE of the sensor system was immersed. The film was obtained after electrodeposition, by CV, when applying a potential range between 0 and 1.9 V at 50 mV/s. Ultimately, the films were analyzed by DPV using melamine solutions, in which case an LOD of \(6.8\times 10^{-8}\) M was calculated [157]. In 2021, [PERSON] et al. [158] proposed the development of an MIP-based sensor for naloxone detection. For this reason, the authors used a MWCNTs modified ITO electrode for the following sol-gel MIP film deposition.