Electrospinning Machine| Fabrication of Dual Photodynamic Enhanced Antimicrobial CDs@ZIF-8/Polycaprolactone/Ethyl Cellulose Nanofibrous Films for Fruit Preservation

Microbial contamination poses a severe threat to food, the environment, and public health, raising widespread concern. Chemical preservatives are commonly used to control microbial growth, but long-term use carries risks such as increased resistance, chemical residue accumulation, and reduced antibacterial efficacy. The World Health Organization predicts that by 2050, microbial resistance will cause nearly 10 million deaths annually. Thus, developing green and efficient antibacterial technologies to avoid resistance is crucial.

Photodynamic antibacterial technology, as a novel non-thermal physical sterilization method, efficiently inactivates microbes by releasing reactive oxygen species. It offers advantages like low resistance risk, safety, broad-spectrum efficacy, low cost, and no toxic byproducts, demonstrating great potential to replace traditional preservatives in food, medical, and environmental fields. Recently, Prof. Wu Di's team at Zhejiang University published a study in Advanced Science titled *"Fabrication of Dual Photodynamic Enhanced Antimicrobial CDs@ZIF-8/Polycaprolactone/Ethyl Cellulose Nanofibrous Films for Fruit Preservation."*

The researchers synthesized CDs@ZIF-8 nanocomposites via coordination self-assembly, achieving dual photodynamic enhancement to kill 7.63 lg E. coli and 7.27 lg S. aureus, outperforming individual CDs (3.12 lg, 4.17 lg) or ZIF-8 (4.18 lg, 2.94 lg). Mechanisms include: (1) ZIF-8 confinement preventing CDs aggregation while broadening light absorption; (2) reduced bandgap promoting e⁻−h⁺ separation and O₂ activation, boosting •O₂⁻ and ¹O₂ generation.

Figure 1:（A）Fabrication process of CDs@ZIF-8 nanocomposites. TEM images of B) CDs, C) ZIF-8, and D) CDs@ZIF-8 nanocomposites. SEM images of E) ZIF-8 and F) CDs@ZIF-8 nanocomposites. G-I) EDX mapping of CDs@ZIF-8 nanocomposites.

Figure 2:Antibacterial tests under different light exposure times for A) S. aureus and B) E. coli. Quantitative changes of C) S. aureus and D) E. coli populations under varying light durations.

Figure 3:A) NBT assay for •O₂⁻, B) RNO assay for ¹O₂, and C) DPBF assay for ¹O₂. Photooxidation rates of D) NBT, E) RNO, and F) DPBF in different treatment groups. G) ROS generation in S. aureus and E. coli under light/dark conditions. Quantitative analysis of ROS levels in H) S. aureus and I) E. coli cells.

Figure 4:A) UV-Vis diffuse reflectance spectra. Bandgap diagrams of B) CDs, C) ZIF-8, and D) CDs@ZIF-8. Mott-Schottky curves for E) CDs, F) ZIF-8, and G) CDs@ZIF-8. H) EIS Nyquist plot. I) Transient photocurrent response. J) Energy level diagrams of CDs, ZIF-8, and CDs@ZIF-8. K) Charge distribution and L) DFT-calculated HOMO/LUMO orbital distributions.

Microbial infection is the primary cause of postharvest spoilage and quality deterioration in fresh fruits, leading to significant food waste. As an effective approach to suppress microbial infection and transmission, packaging serves as a critical solution for delaying fruit decay. Nanofibers, with their advantages of high specific surface area, superior loading capacity, excellent mechanical properties, and tunable structures, have emerged as an ideal carrier for constructing fresh-keeping packaging materials.Addressing the postharvest preservation needs of perishable fruits, this study developed nanofibers as dual photodynamically enhanced antibacterial packaging carriers. Using microfluidic air-jet spinning technology, the CDs@ZIF-8 nanocomposite was precisely incorporated into a polycaprolactone (PCL)/ethyl cellulose (EC) matrix, successfully fabricating CDs@ZIF-8/PCL/EC nanofibrous films. The results demonstrated that the CDs@ZIF-8/PCL/EC nanofibrous films exhibited:Exceptional photodynamic antibacterial performance (>99.99999% bactericidal rate against E. coli and S. aureus)Excellent mechanical propertiesSustained preservation efficacy (extending strawberry shelf life from 6 to 12 days)This study provides novel insights for developing CDs/MOFs synergistically enhanced photodynamic antibacterial nanofibrous packaging materials.

Figure 5:Mechanical properties of CDs@ZIF-8/PCL/EC nanofibrous films: A) Young's modulus, B) tensile strength, C) elongation at break. D) DSC curves. TGA/DTG profiles of PCL/EC nanofibrous films with E) 0%, F) 1%, G) 2.5%, and H) 5% CDs@ZIF-8.

Figure 6:A) Morphological images of strawberries in different treatment groups. Changes in B) L, C) a, D) b*, E) pH, F) TSS, G) weight loss, and H) firmness of strawberries across treatments.

Paper link: https://doi.org/10.1002/advs.202503567