Biosensors Based on MnO2 Nanostructures: A Review

In recent years, a variety of biosensors based on manganese dioxide (MnO2) nanostructures were used for the detection of different biomolecules. Structural versatility and different oxidation states of Mn present in MnO2 nanostructures significantly enhance their biosensing applications. In this review, we have mainly focused on different morphologies of MnO2 nanostructures and their role in different types of biosensors. We are elaborately discussing the electrochemical and optical-based biosensors on different morphologies of MnO2 and their sensing techniques with proposed mechanisms. In electrochemical biosensors, various electrodes are available but there is a need for cheap, flexible, portable, and nontoxic electrodes. Therefore, we have discussed the fabrication of MnO2 nanostructures on the surfaces of different types of electrodes and their real-time applications. MnO2 nanomaterials are used in various optical biosensors due to their excellent light absorption properties, and they act as strong quenching agents. MnO2 nanomaterials are termed "alternative natural enzymes" due to their significant enzyme-like activity. The study of various morphology-dependent sensing properties of MnO2 nanostructures provides an insight into the development of many electrochemical and optical biosensors. Recently, MnO2 based biosensors have earned great popularity as an alternative method for fast and easy detection of many biomolecules with very low detection limits.