## 4 Molecular Imprinting Using MIP Particles Embedded in Pastes or Inks
SPE usually combine a three-electrode configuration (working, reference and counter electrode) printed on different chemically inert substrates, i.e., flexible plastic (polycarbonate, polyimide, polyvinyl chloride and PEEK), ceramic, paper or glass substrates [106]; the substrates are easily modifiable with a great variety of commercial or self-made inks. The pastes most commonly reported in SPE production are conductive (containing the polymer base dispersed in a solvent and the conductive material) or dielectric inks (often based on polymers or ceramics and form the encapsulating layer of the sensor) [98; 107]. Among the solvents that participate in the ink components [108], there are two categories: organic and water-based. Organic solvents, such as ketone, esters and hydrocarbons, in general, have a low flash point, which promotes faster drying of the ink and low viscosity, which are generally qualities that facilitate the processing of inks. Recently, considering the performance and the environmental strategies, water-based inks have also been employed [109; 110; 111]. Gold paste is also employed in SPEs but less than carbon due to its higher cost [112]. The composition of the various inks used for printing on the electrodes determines the selectivity and sensitivity required for each analysis. It is important to point out that proper ink formulation is owned by the manufacturer as proprietary information and it has been shown that differences in ink composition e.g., type, size or loading of graphite particles and in the printing and curing conditions can strongly affect the electron transfer reactivity and the overall analytical performance of the resulting carbon sensors. An extensively studied path used in the preparation of modified layers is based on the incorporation of pre-synthesized MIP microparticles/nanoparticles [113; 114] (acting as a selective recognition element and a pre-concentrator agent for the determination of different templates) into layers or polymer matrices or containing a conducting material and binder (e.g., PVC) (e.g., carbon nanotubes (CNTs), graphene, graphite, or carbon black) [110; 115] (Table 3). [PERSON] and [PERSON] [116] revealed the most significant approaches for electrodes modified with MIP (including spin and drop coating and self-assembling of films on metal nanoparticles). Thus, the mentioned authors used a graphite-polyurethane composite matrix to prepare electrodes used in paracetamol (APAP) determination. Interference of phenacetin in the APAP response decreased remarkably when the proposed electrode was used. [PERSON] et al. [117] described the successful preparation of an MIP nanoparticle/graphene suspension drop-coated as a thin layer onto the surface of the SPCE. For this purpose, two inks including silver ink (containing silver and PVC powders with mass percentages of 97 and 3% respectively in 1:1 (\(v/v\)) acetone/cyclohexanone solution) and carbon ink (containing 80% graphite, 12% dibutyl phthalate (DBP) and 8% PVC in 1:1 (\(v/v\)) acetone-cyclohexanone solution) were prepared. The electrochemical sensor used for the selective detection of an antidepressant drug, sertraline (STR) exhibited good sensitivity (177.25 \(\mu\)A L \(\mu\)mol\({}^{-1}\)) and recoveries above 98%. Another significant study was described by [PERSON] et al. [118], where the team reported the preparation of dual-imprinted electrodes modified with graphene to simultaneously determine 8-hydroxy-20-deoxyguanosine (8-OHdG) and 3-nitrotyrosine (3-NT) and assesses oxidative and nitrative biomarkers in urine and plasma samples. The synthesized composites, mixed separately with graphene ink, were further screened as hydrophobic barrier layers on filter paper. The smart devices revealed selectivity and sensitivity leading to low detection limits of 0.0027 \(\mu\)M for 3-NT and 0.0138 \(\mu\)M for 8-OHdG. In another screen-printing preparation strategy, a graphite ink made of a mixture of graphite powder and hydroxyethyl cellulose was chosen [119].