Dependence of anodic peak current on incubation time
Different peak current responses of the IIP/PAN-MWNTs/CuNPs/CdS/CE, the IIP/CE and the NIP/PAN-MWNTs/CuNPs/CdS/CE were observed with the incubation time increasing from 1 min to 60 min in 1.0 mmol•L-1 Pb(II) complex in Fig. 8B. The IIP/PAN-MWNTs/CuNPs/CdS/CE kept the highest current responses (curve a) compared with the IIP/CE (curve b) and the NIP/PAN-MWNTs/CuNPs/CdS/CE (curve c) for the same incubation time, which shows the excellent selectivity and sensitivity of the prepared sensor. The improved sensitivity of the MIP film could be attributed to the introduction of the PAN-MWNTs/CuNPs/CdS on the IIP/PAN-MWNTs/CuNPs/CdS/CE, for the PAN-MWNTs/CuNPs/CdS could help enhance electron transfer on the electrode interface, and promoted the redox of Pb(II) complex, thus amplified the electrical signal produced by the selective recognition of Pb(II) complex. What is more, it was found that the IIP/PAN-MWNTs/CuNPs/CdS/CE responded quickly to the target molecule even after 1 min of incubation in Fig. 8B-a. The speedy response results from the porous MIP film with plentiful selective binding sites, the PAN-MWNTs/CuNPs/CdS functional layer with electrochemical catalytic activities, and the optimization of the analytical conditions.To prove the precision and practicability of the proposed method, the reproducibility and storage stability of the sensor were also examined. The relative standard deviation of the modified electrode response to 1.0 mmol•L-1 Pb(II) complex was 3.6 % for ten successive measurements. The relative standard deviation for detection of 1.0 mmol•L-1 Pb(II) complex with five sensors prepared under the same conditions was 4.1 %. The modified electrode was stored in pH 7.0 PBS at 25 °C and measured at intervals of 5 days. The sensor retained 99.0 % of its original sensitivity after 5 days, and remained about 92.0 % of its original current after 1 month. This shows that the lifetime of the proposed electrode was about 2 months (shown in Fig. 8C). The excellent reproducibility and stability of the sensor are due to the good compatibility and stability of the IIP/PAN-MWNTs/CuNPs/CdS film. On the one hand, the compatibility of IIP/PAN-MWNTs/CuNPs/CdS film provides an interconnected three-dimensional matrix to deposit Pb(II) complex. On the other hand, the good affinity of IIP/PAN-MWNTs/CuNPs/CdS film to Pb(II) complex improves the electron transfer and prevents leakage of Pb(II) complex from the IIP/PAN-MWNTs/CuNPs/CdS film structure efficiently. The potentiometric selectivity coefficients, describing the preference of the suggested electrode for an interfering ion with reference to the lead ion, Pb2+, were determined by SWV.
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