Study of the Morphology Effect of MnO2 on Carbon Dot Based Nanosensor for the Detection of Biomolecules

Abstract

The thesis entitled Study of the morphology effect of MnO2 on Carbon dot-based nanosensor for the detection of biomolecules is divided into six chapters. Chapter-1. It describes the background of sensor, nanosensor, and fluorescent nanomaterials along with literature survey and scope of the work. This Chapter explains the detail information about the carbon dots (Cdots) with its synthesis approaches, fluorescence mechanism, optical properties, and effect of heteroatom doping. The different fluorescence quenching mechanisms of Cdots in the presence of quencher and different photophysical parameters were also discussed in this Chapter. The exceptional properties of MnO2 and its different morphologies available were also described in this chapter. The importance of biomolecules in living beings and their need for detection by fluorescent probe was explained. Chapter-2. A fluorescent nanosensor based on carbon dots and different-size MnO2 nanospheres has been synthesized for rapid detection of glutathione (GSH). Water-soluble and highly fluorescent Cdots were prepared by the microwave method using ascorbic acid as the precursor. MnO2 nanospheres of different sizes (large, medium, and small) were prepared by varying the concentration ratio of methionine and KMnO4 at room temperature, which was confirmed by HRTEM analysis. The different sizes of MnO2 nanospheres in Cdots result in quenching of the fluorescence intensity, quantum yields, and average lifetime values, which suggest that the fluorescence resonance energy transfer mechanism occurs between the Cdots and MnO2 nanospheres. The variations of all the photophysical parameters and fluorescence turn off properties of Cdots are significantly tuned depending on the size of the nanospheres. Moreover, detection of GSH in the presence of different-size CdotsatMnO2 systems has been explored. GSH causes the redox reaction in the presence of MnO2, which leads to transformation from MnO2 to Mn2+. As a result, fluorescence restoration (turn-on) of Cdots was observed.