Polypyrrole and its composites for electrochemical sensor applications: A review

Polypyrrole (PPy) is an important conducting polymer (CP) with tunable electrical, chemical, and mechanical properties. Its ease of synthesis and stable redox behavior support its use in energy devices, environmental systems, and biosensing. PPy can be prepared by chemical, electrochemical, and template-based routes, each giving materials with distinct morphology and performance. Its ability to form nanostructures and stable composites with carbon materials, metal oxides, and biopolymers further improves conductivity, charge transport, and mechanical strength. These features have led to rapid progress in PPy-based electrodes and flexible devices. PPy is also widely used in electrochemical biosensors because it supports electron transfer, allows ion movement, and provides a suitable microenvironment for enzymes, DNA, antibodies, and imprinted cavities. PPy-based composites show strong responses to biomolecular binding and give stable amperometric, voltammetric, and impedimetric signals. This review summarizes recent developments in PPy synthesis, properties, composite design, and biosensing mechanisms, and highlights emerging opportunities for next-generation PPy-based electrochemical sensors.