When materials approach the size of few nanometers, they show properties which are significantly different from their bulk counterpart. Such unique/improved properties make them potential candidate for several emerging applications. At the reduced dimension, controlling the shape of nanocrystals provides an effective way to tune several material properties. In this regard, wet chemical synthesis has been established as the ultimate route to synthesize nanocrystals at ultra-small dimensions with excellent control over the morphology. However, the use of surfactant poses a barrier into efficient realization of its application as it requires a clean interface for better performance. Exercise of available cleaning protocols to clean the surface often leads to coarsening of the nanoparticles due to their inherent high surface curvature. For anisotropic nanomaterials, rounding of the shape is an additional problem. Anchoring nanomaterials onto substrates provides an easy way to impart stability. In this thesis, ultrathin Au nanowires, that are inherently unstable, have been shown to grow over a wide variety of substrates by in-situ functionalization. Use of nanomaterials as device component holds promise into miniaturization of electronics. But device fabrication in such cases require manipulation of nanomaterials with enhanced control. Dielectrophoresis offers an easy way to assemble nanomaterials in between contact pads and hence evolved as a promising tool to fabricate device with a good level of precision. Herein, directed assembly of ultrathin Au nanowires by dielectrophoresis, has been shown as an efficient strategy to fabricate devices based on the wires. Combining more than one nanocrystal, to form a heterostructure, often has the advantage of synergism and/or multifunctionality. Therefore, synthesis of heterostructure is highly useful in enhancing and/or adding functionalities to nanomaterials. There are several routes available in literature for synthesis of heterostructures. Newer strategies are being evolved to further improve performance in an application specific way. In that regard, a good understanding of mechanism of formation is crucial to form the desired product with the required functionality. For example, Au due to high electron affinity has been known to undergo reduction rather than cation exchange with chalcogenides. In this thesis, it has been shown that the final product depends on the delicate balance of reaction conditions and the system under study using CdS-Au as the model system. In yet another case, PdO nanotubes have been shown to form, on reaction of PdCl2 with ZnO at higher starting ratio of the precursors. In-situ generation of HCl provides an effective handle for tuning of the product from the commonly expected hybrid to hollow. Graphene has evolved as a wonder material due to its wide range of practical applications. Its superior conductivity with high flexibility has made it an important material in the field of nanoelectronics. In this thesis, an interesting case of packed crumpled graphene has been shown to sense a wide variety of strain/pressure which has applications in day to day life. The study reported in the thesis is organized as follows: Chapter 1 presents a general introduction to nanomaterials followed by the review of the available strategies to synthesize various 1D nanomaterials. Subsequently, a section on the classification of hybrid followed by the different synthetic protocols adopted in literature to synthesize them, have been provided. A review on the available methodologies for directed assembly of nanomaterials has been presented. Chapter 2 provides a summary of the materials synthesized and the techniques used for characterization of the materials. A brief description of all the synthetic strategy adopted has been provided. The basic principle of all the characterization techniques used, has been explained. A section explaining the principle of dielectrophoresis has also been presented. Chapter 3 presents a general method to grow ultrathin Au nanowires over a variety of substrates with different nature, topography and rigidity/flexibility. Ultrathin nanowires of Au (~2 nm in diameter) are potentially useful for various catalytic, plasmonic and device applications. Extreme fragility on polar solvent cleaning was a limitation in realizing the applications. Direct growth onto substrate was an alternative but poor interfacial energy of Au with most commercial substrates lead to poor coverage. In this chapter, in-situ functionalization of the substrates have been shown to improve Au nucleation dramatically which lead to growth of dense, networked nanowires over large area. Catalysis and lithography-free device fabrication has been demonstrated. Using the same concept of functionalization, SiO2 coating of the nanowires have been shown. A comparative study of thermal stability of these ultrafine Au nanowires in the uncoated and coated form, has been presented. Chapter 4 demonstrates an ultrafast device fabrication strategy with Au nanowires using dielectrophoresis. While dense growth of Au nanowires is beneficial for some applications, it is not so for some others. For example, miniaturization of electronics require large number of devices in a small area. Therefore, there is a need for methods to manipulate nanowires so as to place them in the desired location for successful fabrication of device with them. In this chapter, dielectrophoresis has been used for assembling nanowires in between and at the sides of the contact pads. Alignment under different conditions lead to an understanding of the forces. Fabrication of a large number of devices in a single experiment has been demonstrated. Chapter 5 presents a simple route to synthesize CdS-Au2Sx hybrid as a result of cation-exchange predominantly. Au due to high electron affinity has been shown in literature to undergo reduction rather than cation exchange with CdS. In this chapter, it has been shown that cation exchange may be a dominant product. The competition between cation exchange and reduction in the case of CdS-Au system has been studied using EDS, XRD, XPS and TEM. Thermodynamic calculation along with kinetic analysis show that the process may depend on a delicate balance of reaction conditions and the system under study. The methodology adopted, is general and may be applied to other systems. Chapter 6 presents an one pot, ultrafast microwave route to synthesize PdO hollow/hybrid nanomaterials. The common strategy to synthesize hollow nanomaterials had been by nucleation of the shell material on the core and subsequent dissolution of the core. In this chapter, a one step method to synthesize hollow PdO nanotubes, using ZnO nanorods as sacrificial template, has been shown. By tuning the ratio of the PdCl2 (PdO precursor) to ZnO, ZnO-PdO hybrid could be obtained using the same method. The PdO nanotubes synthesized could be converted to Pd nanotubes by NaBH4 treatment. Study of thermal stability of the PdO nanotubes has been carried out. Chapter 7 demonstrates a simple strategy to sense a variety of strain/pressure with taped crumpled graphene. Detection of ultralow strain (10-3) with high gauge factor is challenging and poorly addressed in literature. Taped crumpled graphene has been shown to detect such low strain with high gauge factor (> 4000). An ultra-fast switching time of 20.4 ms has been documented in detection of dynamic strain of frequency 49 Hz. An excellent cyclic stability for >7000 cycles has been demonstrated. The same device could be used to detect gentle pressure pulses with consistency. Slight modification of the device configuration enabled detection of high pressure. Simplicity of the device fabrication allowed fabrication of the device onto stick labels which could be pasted on any surface, for instance, floor. Hard pressing, stamping with feet and hammering shocks do not alter the base resistance of the device, indicating that it is extremely robust. Sealed arrangement of the graphene allowed operation of the device under water in detection of water pressure. Presence of trapped air underneath the tape enabled detection of air pressure both below and above atmospheric pressure.

Bio-inspired or biomimetic chemistry deals with the replication of the nature’s fundamental processes, which can help in understanding the functioning of biological systems and develop novel applications. Although a large number of researchers worked towards the replication of natural synthetic pathways through biogenetic syntheses, enzyme mimicry by the small organic molecules and inorganic complexes emerged in leaps and bounds over the years. The development of biomimetic chemistry then continued in designing the molecules that can function like enzymes. And now, with the advent of nanotechnology, nanostructured materials have been shown to exhibit enzyme-like activities (nanozymes). Interestingly, the two distinct fields, biology and materials science, have been integrated to form an entirely new area of research that has captured a great attention. Along with the pronounced application of nanomaterials as drug delivery vehicles, anticancer agents, antimicrobials, etc., research is also focused on designing nanomaterials for the biomimetic applications. The thesis consists of five chapters. The first chapter provides a general overview of the recently discovered nanozymes that mimic heme-peroxidase, oxidase, superoxide dismutase, catalase, haloperoxidase and phosphatase. This chapter also deals with the nanozymes’ application in sensing and immunoassay, and as antioxidants, neuroprotective agents. The factors affecting the nanozymes’ activity and the challenges associated with them is also covered in this chapter. Chapter 2 is divided into two parts and it deals with the biomimetic properties of graphene-based materials. In part A, the remarkable peroxynitrite (PN) reductase and isomerase activities of hemin-functionalized reduced graphene oxide (rGO) is discussed. In part B, the activity of graphene oxide (GO) as peroxide substrate for the glutathione peroxidase (GPx) enzyme is discussed. In chapter 3, the oxidant material, V2O5, is shown to exhibit significant GPx-like antioxidant activity in its nano-form. Chapter 4 deals with the oxidase-like activity of MnFe2O4 nanooctahedrons for the antibody-free detection of major oxidative stress biomarker, carbonylated proteins. In chapter 5, the phosphotriesterase mimetic role of vacancy engineered nanoceria is discussed. instead of H2O2 for glutathione peroxidase (GPx) enzyme. As partial reduction of GO was observed when treated with GPx enzyme due to the fact that large sheet-like structures cannot be accessible to the active site, we studied the reaction with some GPx mimetics (Fig. 2). Varying the concentration of cofactor glutathione (GSH) required for the reaction, GPx mimic, ditelluride, could accomplish the reduction of GO following Michaelis-Menten kinetics. As the structure of GO is elusive and under active investigation, our study highlights the presence of peroxide linkages as integral part of GO other than hydroxyl, epoxy and carboxylic groups. This study also highlights an important fact that the modification of GO by biologically relevant compounds such as redox proteins must be taken into account when using GO for biomedical applications because such modifications can alter the fundamental properties of GO. Figure 2. The GO reductase and decarboxylase activities of GPx mimetic ditelluride compound, suggesting the presence of peroxide linkages on GO. In chapter 3, we have discussed about the novel antioxidant nanozyme that combats oxidative stress. During our attempts in the investigation of antioxidant nanozymes, we surprisingly noticed that the oxidant material, V2O5, shows significant GPx-like antioxidant activity in its nano-form. The Vn readily internalize in the cells and exhibit remarkable protective effects when challenged against reactive oxygen species (ROS). Although Vn has been shown to protect cells from ROS-induced damage, cells treated with bulk V2O5 and few vanadium complexes resulted in generation of ROS and severe toxicity. Detailed investigation on the mechanism of this interesting phenomenon Chapter 4 deals with the development of novel methodology for detection of biomarkers. Inspired by the use of antibodies and enzymes for detection of a specific antigen, we have shown for the first time that the nanozymes can entirely replace antibodies and enzymes in Enzyme-linked Immunosorbent Assays (ELISA). As a specific example, we focused on the antibody-free detection of chief oxidative stress biomarker, carbonylated proteins, as our target. To achieve this, we designed MnFe2O4 nanooctahedrons that can function as oxidase enzyme and form signaling point of detection. We functionalized MnFe2O4 nanooctahedrons with hydrazide terminating groups so that carbonylated proteins can be linked to nanozymes by hydrazone linkage (Fig. 4a). Treatment of various carbonylated proteins (hemoglobin (Hb), Myoglobin (Mb), Cytochrome c (Cyt c), RNase and BSA) coated in well plate with hydrazide-terminated MnFe2O4 nanooctahedrons and then with 3,3’,5,5’-tetramethylbenzidine substrate, resulted in instantaneous detection by well plate reader (Fig. 4b). Considering the challenges and difficulties associated with the conventional methods used to detect such modified proteins, this methodology opens up a new avenue for the simple, cost-effective, instantaneous and entirely antibody-free ELISA-type detection of carbonylated proteins. Our results provide a cumulative application of nanozymes’ technology in oxidative stress associated areas and pave a new way for direct early detection of post translational modification (PTM) related diseases. Figure 4. a) Nanozyme linked to the carbonylated protein coated on a plate through hydrazone linkage. b) General bar diagram showing detection of oxidized (carbonylated) proteins by nanozymes. Synopsis Figure 5. a) A cartoon view of surface of ceria showing vacancy. b) Zoomed portion of high resolution transmission electron microscopic image showing few vacancies on the surface of nanoceria. c) Catalytic mechanism of detoxification of paraoxon at the defect site. In the final chapter, chapter 5, we have discussed about the nanomaterial that can function as phosphotriesterase enzyme. Phosphotriesterase enzyme is a bacterial enzyme that is involved in the rapid hydrolysis of sarin gas-related deadly nerve agents such as paraoxon, parathion and malathion. When encountered with these orgnaophospatetriesters, living beings tend to undergo nerve shock to cause paralysis by inhibiting an extremely important enzyme called acetylcholine esterase. They are also known to cause severe oxidative stress problems and are associated with neurodegenerative disorders. Therefore, curbing the toxic effects and detoxification of these nerve agents is a world-wide concern and many research teams have focused their attention to address this important problem. Working on the development of nanozymes for important problems, we found that nanoceria, especially the vacancy engineered one (Fig. 5a,b), can serve as active mimic of phosphotriesterase enzyme in the presence of N-methylmorpholine (acting as a distal base histidine). Vacancy engineered nanoceria has been shown to catalyze the hydrolysis of high amounts of paraoxon quiet efficiently and within few minutes with very low activation energy and high kcat. Detailed mechanistic investigation revealed that the presence of both Ce(III) and Ce(IV) is very essential for detoxification activity (Fig. 5b). The vacancies on the surface of nanoceria, were the buried Ce(III) ions are directly exposed to the reaction environment, behave as hotspots or enzyme active sites for detoxification reaction (Fig. 5b).