Novel, Speedy, and Eco-Friendly Carboxymethyl Cellulose-Nitrogen Doped Carbon Dots Biosensors with DFT Calculations, Molecular Docking, and Experimental Validation

Carboxymethyl cellulose (CMC) was prepared from sugarcane bagasse (SB) in minutes using a novel microwave method. Additionally, nitrogen-doped carbon dots (N-CDs) were synthesized from SB using the same microwave technique. These materials were crosslinked with CaCl₂ to prepare antibacterial/antifungal hydrogel sensors. In this regard, both CMC@Ca and CMC@Ca-N-CDs exhibited antibacterial activity against <i>Escherichia coli</i> (Gram negative), while only CMC@Ca-N-CDs demonstrated antibacterial activity against <i>Staphylococcus aureus</i> (Gram positive). Moreover, both materials showed antifungal activity against <i>Candida albicans</i>. The molecular docking study demonstrated that CMC@Ca-N-CDs showed good binding with proteins with short bond length 2.59, 2.80, and 1.97 A° for <i>Escherichia coli</i>, <i>Staphylococcus aureus</i>, and <i>Candida albicans</i>, respectively. These binding affinities were corroborated by the observed inhibition zone diameters. Furthermore, fluorescence microscope revealed distinct imaging patterns between Gram-positive and Gram-negative bacteria, as well as pathogenic yeast (fungi). CMC@Ca-N-CDs emitted blue light when exposed to <i>Escherichia coli</i> and <i>Candida albicans</i> (i.e., CMC@Ca-N-CDs/<i>Escherichia coli</i> and <i>Candida albicans</i>), whereas it emitted bright-red light when exposed to <i>Staphylococcus aureus</i> (i.e., CMC@Ca-N-CDs/<i>Staphylococcus aureus</i>). This disparity in the fluorescence-emitted colors is due to the difference in the cell wall of these microorganisms. Additionally, DFT calculations were conducted to substantiate the robust chemical interactions between CMC, Ca²⁺, and N-CDs.