Title：Enhanced Stable and Efficient of Dual-Ligand Zirconium-Based Metal-Organic Frameworks for Synergistic Photodynamic Inactivation
Journal: Small (Weinheim an der Bergstrasse, Germany)
IF:12.1
Original link：https://doi.org/10.1002/smll.202406171
Reporter：Mingge Han-25-master
Porphyins are known for their antibacterial properties by producing toxic singlet oxygen (1O2), but they face challenges such as hydrophilicity, limited lifespan, and low 1O2 yield. On the other hand, triterpenoids like ammonium glycyrrhizinate (AG) have antioxidant and antibacterial properties but lack efficacy and stability. Incorporating them into metal-organic frameworks (MOFs) results in dual-ligand zirconium (Zr)-based MOFs (M-TG), utilizing porphyrin's membrane-disruptive ability and AG's inhibition of bacterial membrane synthesis to produce synergistic antibacterial effects. M-TG addresses the issue of activity loss, increases reactive oxygen species (ROS) production, and extends stability, achieving a significant bactericidal rate of up to 99.999%. This innovative approach maximizes ligand characteristics through synergy, promising major advancements in antibacterial material design.
Porphyrins, used as photosensitizers for photodynamic inactivation (PDI), are limited by hydrophobic aggregation, low ROS yield, and dependence on oxygen environment; ammonium glycyrrhizinate (AG) has antibacterial and antioxidative properties but unstable activity when used alone. Metal-organic frameworks (MOFs) can stably load porphyrins, yet traditional encapsulation methods suffer from difficulties in controlled release of antimicrobial agents and pore blockage. The study innovatively adopts a dual-ligand strategy, integrating porphyrin (TCPP) with AG to construct Zr-MOFs (M-TG), synergistically disrupting bacterial membranes and inhibiting membrane synthesis, significantly enhancing 1O2 yield (2.75 times) and stability (antibacterial rate >98% after 60 days), achieving efficient sterilization (99.999%), low-oxygen effectiveness, and fruit and vegetable preservation, providing new insights for multifunctional MOFs development.
1. Design and Synthesis
By optimizing the ratio of AG to porphyrin (TCPP) (maximum drug loading at 1:0.75), successfully synthesized dual-ligand Zr-MOFs (M-TG). M-TG4 (AG accounts for 6.78%) exhibits the highest yield and stability, with a specific surface area 3.7 times that of conventional MOFs, forming uniform particles (1-2 μm) under acidic conditions. UV spectra and fluorescence spectra confirm AG embedded in the framework, with release curves showing only slow release of small amounts of AG from M-TG, significantly better than physically encapsulated M@G (over 50% released within 40 hours).
2. Structural and Elemental Analysis
FTIR and XRD confirm that M-TG retains the crystal structure of MOFs but with higher stability, with the introduction of AG resulting in decreased vibration frequency of Zr-O bonds. XPS shows peak shifts in C1s (284.08 eV), N1s (397.18 eV), and O1s (531.08 eV), validating AG's participation in framework construction. Nitrogen adsorption experiments indicate that M-TG4 has uniformly distributed micropores of 2.52 nm, optimal adsorption performance, and maximum absolute value of Zeta potential (best stability).
3. ROS Generation
DPBF quenching experiments and EPR detection confirmed that M-TG produces only singlet oxygen (1O2 ) with almost no Type-I ROS. Under light exposure, M-TG generates ROS at a rate 2.75 times faster than MOFs and M@G, remaining highly effective even at low light intensity (4.8 W/m²). Fluorescence stability tests show that M-TG avoids excited-state self-quenching due to increased porphyrin spacing by AG and facilitated oxygen diffusion through pores.
4. Photodynamic Antibacterial Performance
Under simulated supermarket lighting (8-hour light/dark cycle), M-TG achieves over 99.999% sterilization rates against E. coli, S. aureus, and B. subtilis, significantly outperforming MOFs (63.57%) and M@G (33.34% improvement). SEM reveals severe disruption of bacterial membranes, with oxidative stress indicators (decreased ATP, SOD, GSH-Px, increased MDA) confirming the synergistic damage mechanism. After 60 days, the antibacterial rate remains at 98.12%, while M@G fails due to rapid AG release.
5. Synergistic Antibacterial Mechanism
In dark conditions, AG continuously disrupts bacterial membranes (crystal violet staining shows integrity reduced by 51%), synergizing with 1O2 produced by porphyrin upon illumination. DCFH-DA fluorescence imaging shows the highest intracellular ROS intensity in bacteria treated with M-TG, with minimal loss of antibacterial performance in low-oxygen environments (only 12% efficiency reduction in S. aureus experiment compared to 47% in M@G).
6. Preservation Effect
After 9 days, M-TG-treated Chinese cabbage remains green, with VC and chlorophyll retention rates 40% higher than controls, and significant suppression of surface microorganisms. NBT/DAB staining indicates a 50% decrease in ROS accumulation and a 35% drop in MDA content. Safety assessments reveal residual levels <2 mg/kg, cell survival rates >85%, and no metal ion leaching, meeting food-grade application standards.
This study successfully constructs Zr-based MOFs materials M-TG using a dual-ligand strategy, combining porphyrin's photodynamic activity with AG's membrane-disruptive capability to achieve a sterilization rate of 99.999%. Structural characterization and nitrogen adsorption data jointly validate the high-efficiency ROS generation basis of the material. In terms of ROS performance, experiments demonstrate that M-TG's yield is 2.75 times faster than MOFs/M@G, with fluorescence stability and excited-state self-quenching inhibition further supporting its advantages. Antimicrobial mechanisms revealed by oxidative stress indicators confirm the synergistic damage effect, while low-oxygen environment tests verify environmental adaptability. In preservation applications, the preservation effect of Chinese cabbage and safety data both validate its food-grade potential. This research resolves the issues of unstable drug loading and low ROS yield in traditional materials through complementary dual-ligands, first realizing AG as a skeleton ligand, combining long-lasting antibacterial and preservative functions, offering a new paradigm for multifunctional MOFs design.