# Nanomaterials-Based Ion-Imprinted Electrochemical Sensors for Heavy Metal Ions Detection: A Review
## 4 Conclusions and Future Outlook  
Rapid and efficient quantitative detection of trace HMIs is an important issue for health and environmental safety. The combination of IIT and electrochemical sensing gives IIECSs remarkable properties (such as high sensitivity, excellent selectivity, strong thermal/mechanical stability, low LOD, facile preparation, and reusability, etc. ), which makes them excellent candidates for efficient tools for on-site monitoring HMIs, meeting the growing demand. Nonetheless, IIECSs still need to overcome the shortcomings of IIPs due to their small binding capacity, slow mass transfer rate and low recognition sites. Nanomaterials have unique characteristics such as surface functionalization convenience, high electrochemical activity, good compatibility and high electron transfer performance. The integration of nanomaterials with IIECSs can improve the sensitivity, selectivity, stability, LOD and field detection ability of the sensor for detecting HMIs. This review introduced the preparation and sensing mechanism of the nanomaterials-based HMIIECSs, as well as the recent applications of the nanomaterials in this kind of sensors. The nanomaterials-based HMIIECSs exhibit the characteristics of wide concentration range, low LOD, good selectivity, fast response and accurate results in the detection of HMIs, and have become a new focus of research. Many application examples have demonstrated the great potential of IIECSs in the quantitative detection of HMIs with high sensitivity and high selectivity in many real samples. However, there are still some deficiencies and challenges that need to be addressed, such as few electrode types, limited reuse times, limitations of the target testing HMIs, inadequate field applicability, etc. Important efforts are still required to make in the following aspects: (1) More functional monomers and multifunctional monomers need to be developed to improve the sensitivity of HMIIECSs; (2) New nanocomposites are emerging at an increasing speed and will be used in HMIIECSs; (3) Efforts will be made to develop HMIIECSs for simultaneous analysis of multiple HMIs; (4) Robust HMIIECSs for sensitive and selective detection of HMIs via green approaches are worthy of research and application; (5) It is particularly important to further study the formation and recognition mechanism of IIMs with the help of new technology and characterization techniques, especially the HMIs detection mechanism applied in complex water environments and biological samples; (6) The reusability of HMIIECSs and their applicability in complex environments should be explored to facilitate commercial applications; (7) New types of electrodes, such as wide and flat substrate materials (cellulosic paper, electric glass sheets, etc.) need to be developed and modified with IIPs and NPs to achieve better selectivity and electrocatalytic capabilities, thereby improving the commercialization and convenience of use of HMIIECSs; and (8) Exploring new materials and fabrication methods to obtain fast, micro and integrated portable HMIIECSs suitable for field applications will remain a challenging issue in the coming years. Figure 15 summarizes the future outlook and development trends of HMIIECSs. Figure 15: The future outlook and development trends of HMIIECSs. **Author Contributions:** Conceptualization L.Y. and Q.X. ; methodology L.Y., B.X. and Q.X. ; investigation, L.Y., L.S., Q.Z. and J.Z. ; writing-original draft preparation L.Y. and L.S. ; supervision, writing L.Y., B.X. and Q.X. ; drawing L.Y., L.S. and Q.Z. ; technical analysis L.Y., Q.Z., Y.Z., B.Y., B.X. and Q.X. ; writing-review and editing L.Y., L.S. and Q.X. ; funding acquisition L.Y., B.X. and Q.X. All authors have read and agreed to the published version of the manuscript. **Funding:** This work was financially supported by the NSFC of China (Grant No.