Biomass derived self-assembled DNA-dot hydrogels for enhanced bacterial annihilation

A biomass-derived dual crosslinked DNA-nanoparticle hydrogel for visible light-induced photodynamic bacterial inactivation

Sustainability in developing novel nanomaterials (NPs) from biomass sources is a challenging proposition mainly due to the difficulty of infusing or retaining desired chemical functionalities in the biomass substrate. In this study, we demonstrate the synthesis of DNA-nanoparticles (DNA-NP) from onion genomic DNA as a plant biomass source through controlled hydrothermal pyrolysis to retain functional groups in the NPs for predictable downstream chemical transformations. A dual crosslinking scheme was introduced that involves the DNA-NP to form a hydrogel. Chemical crosslinking was achieved through the formation of a Schiff base between the -CHO groups of glutaraldehyde and the amine functionality present on the DNA-NP surface as well as in the nucleobases of the dangling DNA strands of DNA-NP. Simultaneous physical entanglement was attained through hybridization-mediated self-assembly of the dangling DNA strands of the DNA-NP with untransformed onion genomic DNA. As a corollary of the dual crosslinking, the resulting hydrogel not only displayed remarkable mechanical strength but also showed self-healing properties. The ability of the DNA-NP to generate reactive oxygen species (ROS) with visible light irradiation is translated to the hydrogel, making the system potent for biofilm destruction. The high loading efficiency of the model drug ampicillin sodium (Amp) in the hydrogel was achieved which was released in four days. This hints towards the application of the hydrogel through combination antibiotic-antibacterial photodynamic treatment (APDT) as demonstrated here with both Gram-positive and Gram-negative bacteria.

Natural nanogels crosslinked with S-benzyl-L-cysteine exhibit potent antibacterial activity

Biofilm-forming bacteria E. coli and P. aeruginosa have both exhibited resistance against multiple antibiotics in clinical settings. To find a solution, researchers have turned to antibacterial structurally modified from natural materials that are harmless to the human body. Among these is DNA, a natural polymer composed of deoxyribose that when treated with HCl exposes its aldehyde groups and produces DNA-HCl. Here, we crosslinked these aldehyde groups with the primary amines in S-benzyl-L-cysteine (SBLC) using a Schiff reaction to obtain DNA-HCl-SBLC. We additionally treated alginate acid (AA) with EDAC, obtaining AA-EDAC, and substituting it with SBLC to produce AA-SBLC. We incorporated the above reactions with an emulsification process to produce nanogels (NGs) that were verified to be spherical and possessing benzene rings successfully grafted onto DNA-HCl and AA-EDAC. These natural NGs were proven to be negatively charged through zeta potential analysis and presented low cytotoxicity toward normal cells in cell organoid viability assays. These SBLC-modified polymers provided better inhibition of bacterial growth than those without modification. Moreover, after incubation with SBLC-modified NGs, bacteria expressed intracellular recA or pvdA in a dose-dependent manner, which was consistent with SEM data from damaged bacteria. Out of four tested NGs, DNA-HCl-SBLC NGs suppressed P. aeruginosa-induced sepsis most effectively and extended the lifespan of C. elegans. This study provides an alternative clinical solution to antibiotics-resistant biofilm strains.