Carboxymethyl hemicellulose hydrogel as a fluorescent biosensor for bacterial and fungal detection with DFT and molecular docking studies.

A new method was developed to quickly produce carboxymethyl hemicellulose (CM-Hemi) and fluorescent nitrogen-doped carbon dots (N-CDs) from sugarcane bagasse (SB). These materials were then combined with calcium chloride (CaCl₂) to create hydrogel sensors with antibacterial and antifungal properties. The CM-Hemi@Ca-N-CDs hydrogel was effective against both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria compared to CM-Hemi@Ca which give no antibacterial activity. Both hydrogels also exhibited antifungal properties against Candida albicans. Molecular docking studies revealed that the CM-Hemi@Ca-N-CDs hydrogel had strong binding interactions with the protein from Staphylococcus aureus and Candida albicans (1.92 A°) compard to Escherichia coli (2.01 A°), which was aligned with the inhibition zone measurements from the antibacterial test. The fluorescence microscope revealed differences in the emitted light color when the hydrogel interacted with different types of microorganisms, likely due to variations in their cell walls. Density functional theory (DFT) calculations indicate that the incorporation of N-CDs into the CM-Hemi@Ca hydrogel enhances its stability and rigidity. This is evidenced by the lower energy gap (E), higher electron affinity (μ), and lower softness (S) of the CM-Hemi@Ca-N-CDs compared to the CM-Hemi@Ca hydrogel. Additionally, the formation of amide bonds between the N-CDs and CM-Hemi contributes to the increased rigidity of the hydrogel.These findings supporting th effectiveness of CM-Hemi@Ca-N-CDs as an antibacterial/antifungal sensor.