# Nanomaterials-Based Ion-Imprinted Electrochemical Sensors for Heavy Metal Ions Detection: A Review
## 3 Application of Nanomaterials in HMIIECSs
### Magnetic Ferric Oxide Nanomaterials  
Magnetic nanomaterials (MNMs) are considered promising support materials in analytical chemistry and have been used in separation/extraction and sensor/biosensor applications. Their wide application is mainly due to their superparamagnetism, low toxicity, high biocompatibility and high surface volume ratio [128]. Magnetic material is mainly used as a kind of nanomaterial to improve the morphology and sensitivity of MIP based sensor interface. In the construction of sensing interfaces, after the modification of magnetic materials or magnetic composites, MIP films are usually constructed by electropolymerization due to its simple and effective operation. Sol-gel electrodeposition is also a potential method to prepare MIP films and improve MIP properties, which has been used to construct MIP films at the interface of magnetic molecularly imprinted electrochemical sensors (MMIECS) [129]. As an ideal adsorbent, Fe\({}_{3}\)O\({}_{4}\) nanomaterials have been widely used as ECSs for the detection of HMIs, and the quasi-spherical Fe\({}_{3}\)O\({}_{4}\) nanomaterials with an average diameter of about 10 nm can be used for the independent detection of multiple HMIs [130]. [PERSON] and [PERSON] prepared a voltammetric sensor (Fe\({}_{3}\)O\({}_{4}\)@SiO\({}_{2}\)@IIP@CPE) for selective detection of Ag\({}^{+}\) base on magnetic Ag\({}^{+}\)-IIP NPs, which was achieved by imprinting Ag\({}^{+}\) on silica-coated magnetic NPs (Fe\({}_{3}\)O\({}_{4}\)@SiO\({}_{2}\)) in the presence of PAN, MAA, EGDMA,APS and AgNO\({}_{3}\)[131]. DPV was employed to measure pre-enriched Ag\({}^{+}\) on the surface of Fe\({}_{3}\)O\({}_{4}\)@SiO\({}_{2}\)@IIIP@CPE. Under optimal conditions, it showed a linear response in the concentration range of 0.05-150 \(\mathrm{\SIUnitSymbolMicro\text{g}}\)/L with a LOD of 15 ng/L, remarkable selectivity and good reproducibility (RSD of 4.7%). [PERSON] et al. prepared IIP NPs on vinyl functionalized magnetic Fe\({}_{3}\)O\({}_{4}\) NPs with the surface imprinting process and combined it with MWCNTs to modify CPE for monitoring Pb\({}^{2+}\)[132]. The best response to Pb\({}^{2+}\) (the concentration range of 3-55 \(\mathrm{\SIUnitSymbolMicro\text{g}}\)/L with a low LOD of 0.5 \(\mathrm{\SIUnitSymbolMicro\text{g}}\)/L) was obtained when the CPE was composed of 53% (\(w\)/\(w\)) of graphite powder, 10% of MWCNTs, 7% (\(w\)/\(w\)) of Pb\({}^{2+}\)-IIP, and 30% (\(w\)/\(w\)) of paraffin oil. The designed electrochemical sensor also displayed remarkable selectivity and good reproducibility with RSD of 3.1%. It was applied to determine the content of Pb\({}^{2+}\) in different environmental water samples, and the results were confirmed by graphite furnace atomic absorption spectrometry (GF-AAS). [PERSON] et al. developed a novel electrochemical sensor for determination of Co\({}^{2+}\) based on IIT directly onto the surface of functionalized magnetic NPs (MNPs) modified GCE [61]. The IIP nanobeads was polymerized with AAM as the functional monomer, NNMBA as the crosslinker and APS as the initiator, and around the complex between Co\({}^{2+}\) and 8-hydroxyquinoline groups linked to the casted MNPs at the surface of GCE. Grafting IIP onto the functionalized MNPs improved the specific surface area and adsorption capacity. Preparation of the sensor is shown in Figure 13. Under optimal conditions, the sensor showed a linear range of 0.5 to 20 nM and 20 to 500 nM with a LOD of 0.1 nM. The sensor had the advantages of simple design, short measurement time, high accuracy, a large amount of analysis, low LOD, and good selectivity. It has been successfully applied to the determination of low level of Co\({}^{2+}\) in different practical samples. In 2018, [PERSON] et al.