# Nanomaterials-Based Ion-Imprinted Electrochemical Sensors for Heavy Metal Ions Detection: A Review
## 3 Application of Nanomaterials in HMIIECSs
### Carbon-Based Nanomaterials
#### 3.1.2 Graphene Materials
After optimization, the linear relationship was observed in the range of 0.5-100 \(\upmu\)M, and the LOD was 0.15 \(\upmu\)M. Conventional metal ions had little interference in the detection of Cu\({}^{2+}\), and the CS/GO-IIP/GCE showed good reproducibility with an RSD of 3.3% by repeated DPASV. Moreover, the performance of the CS/GO-IIP/GCE was validated in tap and river water samples with acceptable recoveries. [PERSON] et al. designed a highly selective and sensitive electrochemical sensor based on IIP and GO (IIP/GO@GCE) by a drop coating technique for Cd(II) monitoring in different real samples [106]. The Cd(II)-IIP was successfully prepared using the new complex agent and functional monomer of ethyl 6-(allyoxy)-2-amino-4-phenyl-4H-benzo[f]chromene-3-carboxylate (EAAP), the initiator of AIBN and the crosslinker of EGDMA. As shown in Figure 8, GO had high conductivity and a large surface area, which facilitated the electron exchange of cadmium ions. Moreover, after fixing the leached IIP, it was found that the peak current intensity increased significantly. The electrochemical response of IIP/GO@GCE for Cd(II) was investigated by ASV, which showed a wide detection range of 4.2 \(\times\) 10\({}^{-12}\)-5.6 \(\times\) 10\({}^{-3}\) M and a very low LOD of 7 \(\times\) 10\({}^{-14}\) M. In addition, the new developed sensor also achieved good selectivity, high repeatability and stability. \begin{table}
\begin{tabular}{c c c c c c c} \hline
**Target Ion** & **Electrode** & **Nanomaterial** & **Monomer** & **Electrochemical Method** & **Linear Range (\#M)** & **LOD (\#M)** & **Ref.** \\ \hline Pb\({}^{2+}\) & GCE & AuNPs/GR/MWCNTs & CS & DPV & \(1.00\times 10^{-3}\)-50 & 2.83 \(\times\) 10\({}^{-4}\) & [66] \\ \hline \multirow{3}{*}{Cd\({}^{2+}\)} & GCE & AuNPs/GR & CS & DPV & -0.10-90 & 1.62 \(\times\) 10\({}^{-4}\) & [25] \\  & GCE & RGO & PPy & SWASV & 8.90 \(\times\) 10\({}^{-3}\)–0.89 & 2.30 \(\times\) 10\({}^{-3}\) & [67] \\  & GCE & ERG & PoFD & SWASV & 8.90 \(\times\) 10\({}^{-3}\)–0.44 & 1.20 \(\times\) 10\({}^{-3}\) & [68] \\  & GCE & N-GO & CS & DPV & 0.01–0.10 & 3.51 \(\times\) 10\({}^{-3}\) & [33] \\ \hline \multirow{2}{*}{Hg\({}^{2+}\)} & GCE & AuNPs/SWCNTs & Mercapobenzotriazole & DRASV & 4.00 \(\times\) 10\({}^{-4}\)–9.60 \(\times\) 10\({}^{-2}\) & 8.00 \(\times\) 10\({}^{-5}\) & [69] \\  & GCE & Au/ZnO & Py & SWV & -1 \(\times\) 10\({}^{-6}\) & [70] \\ \hline As\({}^{1+}\) & GE & NPG & P-phenylened-amine & CV & 2.00 \(\times\) 10\({}^{-5}\)–9.00 \(\times\) 10\({}^{-3}\) & 7.10 \(\times\) 10\({}^{-6}\) & [71] \\ \hline \end{tabular}
\end{table} 
Table 2: Summary of the HMIIECSs prepared by electropolymerization. Figure 7: Schematic diagram of the fabrication procedure for CS/GO-IIP/GCE (**1**) and the corresponding chemical processes involved (**2**). Note: the outer green layer is not GCE but the electrode insulation; GCE is the black inner disk. Reprinted with permission from Ref. [65]. Copyright 2019, Elsevier. [PERSON] et al. developed a Cu\({}^{2+}\)-selective electrode with a highly selective potential response to Cu\({}^{2+}\) based on GO/MWCNT/Cu\({}^{2+}\)-IIP composite, which was composed of GO (65.0% (_w/w_)), MWCNT (5.0% (_w/w_)), Cu\({}^{2+}\)-IIP (20.0% (_w/w_)), and paraffin oil (10% (_w/w_)) [27]. The Cu\({}^{2+}\)-IIP was synthesized by using EGDMA as the crosslinker, AIBN as the free radical initiator, and Cu\({}^{2+}\)-5-methyl-2-thiozymethacrylamide monomer complex, and was first used as an electroactive component in an ion-selective electrode. The electrode showed a linear response in the concentration range of 1.0 \(\times\) 10\({}^{-6}\)-1.0 \(\times\) 10\({}^{-1}\) M (the correlation coefficient was 0.9998) with the sensitivity of 26.1 \(\pm\) 0.9 mV decade\({}^{-1}\) and the LOD of 4.0 \(\times\) 10\({}^{-7}\) M. In the range of pH 4.0-8.0, it was stable and reversible with a rapid potential response of 3 s and a lifetime of more than 1 year. Satisfactory results were obtained in potentiometric titration and real water sample determination.