## 3 Results and Discussion
### Electrochemical Behaviour of GO-MIPs  
The modified electrodes were prepared by simply dropping the obtained GO-MIP nanocomposite dispersion on a freshly polished glass carbon electrode (GCE) and then drying it. The surface status and the barrier of the different modified electrodes could have been monitored by the CV using potassium ferrocyanide as a probe [42]. Figure 7a shows the CV responses of four different modified electrodes in a 5.0 mM K\({}_{3}\)[Fe(CN)\({}_{6}\)] solution and 0.1 M KCl. In the case of the bare GCE, the typical reversible process of the electrochemical response for [Fe(CN)\({}_{6}\)]\({}^{3-}\) was observed. With the unique electric conductivity, the redox peak current was shown to increase for GO/GCE compared with bare GCE. As for GO-MIPs/GCE, the electrochemical behavior was equal to or slightly superior to GO/GCE, which could be explained by the possibility that the [Fe(CN)\({}_{6}\)]\({}^{3-}\) molecules could easily reach the surface of the electrode through the vacant cavities. In contrast, the redox peak current of [Fe(CN)\({}_{6}\)]\({}^{3-}\) declined dramatically after GCE was coated with GO-NIPs, which could be due to the weak conductivity of dense polymers. The  
Figure 6: The selectivity of the GO-MIPs and GO-NIPs for adsorption of 4-MEC and interfererents in aqueous medium (**a**), and repeatability experiments of GO-MIPs over six cycles of adsorption–desorption in methanol of the extraction at ambient temperature (**b**).  
successful fabrication of the GO-MIPs sensor was further verified by DPV, and the results were in good agreement with the CV results. As shown in Figure 7b, the distinct redox peak of [Fe(CN)6]3- was found to be at around 0.2 V, and the peak current of GO-NIPs/GCE was significantly lower than those of bare GCE, GO/GCE, and GO-MIPs/GCE, providing direct evidence of vacant cavities in the GO-MIPs.  
As the performances of the GO-MIP composite modified electrode showed the advantages of good electrical conductivity, excellent selectivity, and high cycle stability, it possesses potential in the applications of electrochemical sensors. To further validate the selectivity of the GO-MIP composite modified electrochemical sensor, the current responses to 4-MEC, 4-MMC, 4-MDMC, THF-F, and MO were detected in a K\({}_{3}\)[Fe(CN)6] solution, respectively. When the vacant cavities were attached with the adsorbate molecules, the response current decreased, and as a result, the reduction peak current (\(\Delta I\)) could be used to represent the adsorption ability of the imprint sites for different adsorbate molecules. As seen in Figure 8a, the electrochemical sensor showed a much larger value of \(\Delta I\) for 4-MEC than for the other four potential interferents at the same concentration. DPV analysis was done for different concentrations of 4-MEC from 5 to 100 \(\mu\)g mL\({}^{-1}\) under optimized conditions (Figure 8b). With an increase in the 4-MEC concentration, the redox peak current decreased significantly. The calibration curve presented in Figure 8c showed a linear relationship over the range of 5-60 \(\mu\)g mL\({}^{-1}\) with the equation y = 0.4344x + 6.6320, and the correlation coefficient (R\({}^{2}\)) was demonstrated to be 0.9925. Moreover, the signal-to-noise (S/N) ratio was considered as 3 to estimate the limit of detection (LOD) for 4-MEC. The LOD was calculated as 0.438 \(\mu\)g mL\({}^{-1}\) from the slope (m) and the standard deviation (S) was calculation by Equation (6).  
\[LOD=\frac{3S}{m} \tag{6}\]  
Figure 8: Selectivity of GO-MIPs/GCE toward different interferents (**a**), DPV responses of GO-MIPs/GCE for various concentrations of 4-MEC (**b**), and dependence of \(\Delta I\) on the concentration of 4-MEC (**c**) in a solution containing 5.0 mmol L\({}^{-1}\) of K\({}_{3}\)[Fe(CN)6] and 0.1 mol L\({}^{-1}\) KCl.  
Figure 7: CV curves (**a**) and DPV curves (**b**) of bare GCE, GO/GCE, GO-NIPs/GCE, and GO-MIPs/GCE in a solution containing 5.0 mmol L\({}^{-1}\) of K\({}_{3}\)[Fe(CN)6] and 0.1 mol L\({}^{-1}\) KCl.