Nanozyme Vesicles from Gemini Surfactant and Mn-Doped Carbon Quantum Dots for Glucose and Cholesterol Sensing

Nanozymes have attracted substantial scientific interest due to their considerable practical significance regarding the instability, complex fabrication, and higher cost corresponding to protein enzymes. However, their activity is often restricted to narrow pH ranges with peak performance occurring under acidic conditions. In this work, the self-assembly comprising a cationic gemini surfactant and negatively charged manganese-doped carbon quantum dots (Mn-CQDs) leading to the formation of vesicles was investigated. The electrostatic interaction between the negatively charged Mn-CQDs and the positively charged gemini surfactant is the key mechanism behind the self-assembly. Confocal microscopy (CLSM) and field-emission scanning electron microscopy (FESEM) were used to analyze the morphological structures of the self-assembled vesicles. The CLSM images revealed that self-assembled vesicles successfully loaded the dye rhodamine B (RhB) without causing any structural change. The kinetics and catalytic activity of these vesicles were studied using UV-visible spectroscopy to detect peroxidase-like activity. Vesicles acted as nanoreactors by producing a confined, organized structure where the substrate and catalyst combine well to accelerate forward reactions. Finally, a cascade reaction using cholesterol oxidase (ChOx) and glucose oxidase (GOx)-loaded vesicles was employed for the colorimetric detection of cholesterol and glucose, achieving detection limits of 288.75 and 336.73 nM, respectively. Our work highlights a straightforward and robust strategy for creating functional optically active hybrid vesicles, offering potential utility in bioanalysis applications, biotechnology, and environmental chemistry.