## 7 Conclusions  
This review provided an overview on the progress of MIP layers synthesized by various modern and dedicated techniques such as surface polymerization, electopolymerization, sol-gel technique, phase-inversion and hybrid methods including MIP-dopped inks/pastes or combined methods of sol-gel and electropolymerization. In this respect, using different systems of monomers, template molecules and solvents, some very sensitive and promising sensing tools were developed. In most of the cases, the sensors showed high sensitivity, selectivity, reproducibility and most importantly, low limit of detection. However, electropolymerization seems to be by far the most promising method to prepare highly sensitive sensors, especially MIP-based electrochemical sensors. From the examples described in Section 3, for detecting different pollutants (dyes, polycyclic aromatic hydrocarbon), drugs (antibiotics), illicit drugs (cocaine), the reported limit of detection for such sensors ranges from 1 \(\upmu\)M to 1 fM. On the other hand, the combined sol-gel/electropolymerization and ink-based sensors are somewhat less complex and cheaper to produce, but with higher values of LOD, in the \(\upmu\)M range. It is also important to note that surface modification or the sol-gel technique is usually preferred for preparing optical and spectroscopic sensors, while the phase inversion method is more applicable to electrochemical sensors and chromatographic applications. Although the electrochemical sensors are generally the most sensible, the use of MIP for \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Synthesis Method** & **Receptor** & **Support** & **Analyte** & \begin{tabular}{c} **Characterization** \\ **Methods(s)** \\ \end{tabular} & **LOD** & **Refs.** \\ \hline Casting & MIP film & Ti/TiO\({}_{2}\) electrode & Bisphenol A & \begin{tabular}{c} Amprometric \\ measurements \\ \end{tabular} & \(1.3\times 10^{-9}\) M & [173] \\ Casting & Hybrid & \begin{tabular}{c} MIP membrane \\ \end{tabular} & Glass support & Citrinin & Batch binding, HPLC 1 & \(0.5\) ng g\({}^{-1}\) & [182] \\ Casting & MIP Membrane & Conductive graphite & Trimethoprim & \begin{tabular}{c} Potentiometric \\ measurements \\ \end{tabular} & \(4.01\times 10^{-7}\) M & [184] \\ Casting & MIP Membrane & Conductive graphite & Enrofloxacin & \
\begin{tabular}{c} Potentiometric \\ measurements \\ \end{tabular} & \(0.9\) ug\(\cdot\)mL\({}^{-1}\) & [185] \\ Dropwise & MIP Film &
\begin{tabular}{c} Screen-printed \\ gold electrode \\ \end{tabular} & Regenerating Protein 1B & CV 2 & \(0.1\) pg\(\cdot\)mL\({}^{-1}\) & [186] \\
3D-Imprinting & MIP Membrane & \
\begin{tabular}{c} Polyvinylidene \\ fluoride/carbon \\ black membrane \\ \end{tabular} & Non-woven &
\begin{tabular}{c} Morpho-structural, CV \\ and 500 mesh fabric \\ \end{tabular} & / & [187] \\ \hline \hline \end{tabular}  
* High performance liquid chromatography; 2 CV: cyclic voltammetry.  
\end{table} 
Table 5: MIP-based sensors obtained by phase inversion method. other detection techniques led in some cases to significant improvements of sensibility and selectivity relative to the state-of-the-art of detection methods applied for optical, spectroscopic or chromatographic applications. Future challenges in the field of MIP layer preparation targets further improvements of the sensitivity, selectivity and reproducibility for real sample applications, especially for peptides and protein detection [42; 44; 45]. Due to the intrinsic properties of the MIP sensors such as robustness, reliability, accuracy, reproducibility, long-term stability and portability, future requirements should be considered in scenarios where MIP layers can potentially be tools for routine applications. For instance, MIP layers for optical biosensors could have a significant impact in targeted applications considering that users are interested in solutions with low maintenance and servicing, such as for environmental monitoring (e.g., screening of estrogen [188] or the sensing of small organic contaminants [189; 190]).