Biosensors Based on MnO₂ Nanostructures: A Review

Abstract

In recent years, a variety of biosensors based on manganese dioxide (MnO 2 ) nanostructures were used for the detection of different biomolecules. Structural versatility and different oxidation states of Mn present in MnO 2 nanostructures significantly enhance their biosensing applications. In this review, we have mainly focused on different morphologies of MnO 2 nanostructures and their role in different types of biosensors. We are elaborately discussing the electrochemical and optical-based biosensors on different morphologies of MnO 2 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 MnO 2 nanostructures on the surfaces of different types of electrodes and their real-time applications. MnO 2 nanomaterials are used in various optical biosensors due to their excellent light absorption properties, and they act as strong quenching agents. MnO 2 nanomaterials are termed "alternative natural enzymes" due to their significant enzyme-like activity. The study of various morphology-dependent sensing properties of MnO 2 nanostructures provides an insight into the development of many electrochemical and optical biosensors. Recently, MnO 2 based biosensors have earned great popularity as an alternative method for fast and easy detection of many biomolecules with very low detection limits.

α‐MnO2‐Sensitized SrCO3−Sr(OH)2 Supported on Two‐Dimensional Carbon Composites as Stable Electrode Material for Asymmetric Supercapacitor and Oxygen Evolution Catalysis

“…It means an improved electrochemical impedance phenomenon at MSSG‐1 loaded electrode was mainly due to the synergistic effect between the SSG composite and the existence of nanostructured MnO 2 . Notably, the presence of folded rGO nanosheets allow to increase the specific surface area and acts as an excellent conductive material with amine functionalities [61] . Meanwhile, the agglomerated MSSG‐2 or MSSG‐3 loaded electrode materials led to decrease the electrochemical utilization of hydroxyl ions during the charging and discharging process.…”

“…Besides, MSSG‐1 loaded electrode holds the energy density of 3.46 Wh/Kg at a power density of 293.6 W/kg even at higher current density of 5.5 A/g. This is due to the enlarged tunnel size of phase oriented α‐MnO 2 that facilitates the accessibility of electrolyte ions throughout the surface and interior of the electrode's material [61,62] . Thus, MSSG‐1 loaded electrode desperately owns sufficient energy or power density for energy storage applications.…”

“…Generally, MnO 2 nanostructures exhibiting the oxygen vacancies for reduction and oxidation reaction intermediates, especially for those involving oxygen reactions such as water oxidation. Importantly, the tunnel structure of α‐MnO 2 do facilitate the access of reactant molecules such as OH − to the active reaction sites [61,72,73] . Moreover, SrCO 3 −Sr(OH) 2 and α‐MnO 2 provide sufficient surface active sites for enhancing the mass/electron transport during the OER process.…”

Recent advances in heteroatom-doped graphene quantum dots for sensing applications

“…129 The electrochemical sensor converts the chemical reactions into electrical signals of the analytes which occur onto the surface of the electrode, thereby providing its surrounding information. 130,131 The electrochemical approaches are less expensive, highly sensitive, simple operation, and easy to handle, therefore attains extensive applications in the eld of medicines, sensing, environmental science/monitoring, and food analysis. 132 Hence, the electrochemical sensors have gained great interest as compared to current existing sensors in analytical chemistry.…”

Electrochemical sensors for the detection of SARS-CoV-2 virus

“…There is an urgent need for a rapid and highly sensitive method to monitor the pandemic. In this respect, electrochemical methods are considered as sensitive, simple to operate, rapid and cost-effective as well as they are easy to use, requiring lesser time to analyze [25] , [26] , [27] , [28] , [29] , [30] , [31] , [32] , [33] , [34] , [35] , [36] . This has prompted to develop various electrochemical techniques to test and identify COVID-19.…”