Functionalized conjugated polymers for sensing and molecular imprinting applications

The electronic conjugation between each repeat unit in conducting polymers (CPs) provides semiconducting molecular architectures and intriguing properties to suit for sensing applications. Therefore, considerable progress has been demonstrated on sensor designs with CPs. Unfortunately, the most essential requirements of sensors such as selectivity of an analyte and detection of a specific analyte in a complex environment are hard to achieve with pristine CPs. These constraints in pristine CPs along with processability limitations necessitate the development of functionalized CPs (FCPs) through intelligent structural modification of pristine CPs or inclusion of a functional property modifying components with CPs. On perusal of the literature in last 10-15 years on the use of FCPs for sensor application reveal that FCPs can out-perform basic function at the molecular levels, such as recognition and control of chemical processes, as well as inform that the unique physical, chemical and electrochemical properties of FCPs could be effectively exploited to improve the selectivity, sensitivity, and throughput of sensors beyond the limits of existing detection techniques. Herein, we provide the first review of FCP materials utilized for sensor fabrications highlighting, in particular, the advances in the synthesis of FCPs employing strategies for the inclusion of functional group/functional component(s) to suit for sensing the specific analyte(s), the improvements in sensor performances (detection limit and linear range) and the role of FCPs in the sensing process. The in-depth analysis of the literature on the use of FCPs for sensors suggests that these research activities are rapidly maturing at the convergence of nanotechnology and biotechnology. We arrange the great number of FCPs utilized for sensing element into four categories; substituted or derivatized FCPs (category I), biofunctionalized FCPs (category II), nanostructured FCPs (category III) and multicomponent FCPs (category IV). This review highlights prominent examples of FCPs as applicable to main type of CPs such as polypyrrole, polyaniline, polythiophene, polyfluorene and other CPs. We also identify how certain functionalization improves sensor performances. In addition, this review presents a discussion of state of the art of FCPs used in the preparation of molecular imprinted polymers (MIPs) intended for molecular recognition/sensor applications. In the final stage, we summarize the characteristics of FCPs with relevance to MIP and sensor designs and propose several prospectives for using FCP as a new sensing platform for the development of next-generation sensors.