Immobilization of Molecular Assemblies on 2D Nanomaterials for Electrochemical Biosensing Applications

Abstract

Immobilization or surface functionalization of molecular assemblies is of tremendous importance in the field of building functional micro/nanolevel devices for a wide range of applications starting from sensing, catalysis, photovoltaics, fuel cells and biomaterials to molecular electronics. Research in this area contributes as well to provide fundamental understanding of electron transfer, controlling reactions at surfaces, and tailoring surface properties. During the last few decades, we have witnessed significant advances in the area of electronics which has resulted in the development of highly compatible and simple electrical transducers from which we can process signals in a highly efficient manner than ever before. Biosensors are analytical tools whose applications stretch out in areas like health care, environment, agriculture and biotechnology. Electrochemical transducers are of highly advantageous in the fabrication of biosensors owing to their simplicity, amenability for field measurements and miniaturization, adaptability for wireless transmission and so on. The challenging task in the fabrication of biosensors is to effectively immobilize/functionalize the molecular recognition assemblies on to the electrode surface with their properties intact. High surface area materials with suitable functional groups that can be electrically wired to electrode surfaces efficiently for effective sensing are required for the fabrication of biosensors. Currently, two-dimensional (2D) materials have evolved as promising potential candidates in electrically transduced chemical sensing. They provide a large surface-to-volume ratio for substrate–analyte interactions when compared to their 0D, 1D and 3D analogues, which is essential for improving sensitivity and through the incorporation of known recognition centres like enzymes, or ligands, onto the surface of 2D materials selectivity is ensured. Apart from the well-studied 2D nanomaterial graphene, a diverse range of 2D materials like phosphorene, hexagonal boron nitride (h-BN), transition metal dichalcogenides (TMDCs), layered metal oxides, 2D metal–organic frameworks (MOFs), covalent organic frameworks (COFs) and other 2D compounds are being explored for biosensing recently. This book chapter will describe how the molecular recognition moieties like enzymes, ligands, ionophores, antigens/antibodies, host molecules, etc., would be immobilized on the 2D materials. Case studies from the literature and few examples from the authors’ work would be highlighted.