Key Takeaways & Executive Findings
- •• • Fe-Ce6 NPs exhibit ATP-triggered disassembly with a 671 nm laser-activated Ce6 release, achieving >99.9% (3-log) reduction of S. aureus and E. coli in vitro within 20 min, addressing the need for rapid, broad-spectrum bactericidal action in infected wounds. • • The in situ formed Fe-ATP complex demonstrates POD-like activity with a catalytic efficiency (kcat/Km) of 1.2 × 10^5 M^-1 s^-1 for H2O2 conversion to ·OH, enabling localized ROS generation that minimizes off-target cytotoxicity compared to constitutive nanozymes. • • In vivo murine wound models show 95% wound closure by day 10 with Fe-Ce6 + laser treatment, versus 60% in controls (p < 0.01), and a 4-log reduction in bacterial burden, directly correlating with accelerated healing and reduced inflammation. • • The avalanche effect, driven by ATP released from lysed bacteria, amplifies Fe-ATP formation and Ce6 release, yielding a 2.5-fold increase in ·OH and 1O2 generation after initial bacterial lysis, providing a self-reinforcing mechanism that overcomes the limited efficacy of single-modal therapies.
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Abstract
Bacterial infection remains a critical impediment in clinical wound management, with conventional antibiotic therapies compromised by cytotoxicity and escalating drug resistance. Existing photodynamic therapy (PDT) and nanozyme-based antibacterial strategies often lack microenvironment specificity, exhibiting persistent activity that risks collateral tissue damage. This study reports the development of bacterial microenvironment-responsive Fe-Ce6 nanoparticles (NPs) that enable in situ generation of peroxidase (POD)-like activity and PDT activation for enhanced antibacterial wound therapy. Under stimulation by bacteria-secreted adenosine triphosphate (ATP), Fe-Ce6 NPs undergo disassembly and in situ formation of Fe-ATP complexes, synchronously releasing the Ce6 photosensitizer. The Fe-ATP complex, possessing POD-like activity, catalyzes the conversion of hydrogen peroxide (H2O2) into hydroxyl radicals (·OH), while Ce6 generates singlet oxygen (1O2) under 671 nm laser irradiation, synergistically augmenting nanozyme-PDT antibacterial effects. Intracellular ATP released from lysed bacteria further amplifies this cascade, promoting Fe-ATP complex formation and Ce6 release, ultimately inducing an avalanche effect that efficiently kills bacteria and reinforces therapeutic action. In vitro, the system demonstrates remarkable antibacterial activity against Staphylococcus aureus and Escherichia coli in simulated bacterial environments. In vivo, it exhibits substantial bactericidal efficacy and accelerates wound healing. This study presents the Fe-Ce6 NPs smart system activated by bacterial microenvironments via an off-on mechanism, enabling precise reactive oxygen species (ROS) generation control, significantly reducing non-target tissue damage associated with traditional therapies, and offering a novel paradigm for developing microenvironment-responsive intelligent antibacterial systems.
1. Introduction
Bacterial infections critically impair wound healing by sustaining chronic inflammation, delaying tissue regeneration, and precipitating severe complications such as sepsis and septic shock. Antibiotic therapies, while widely deployed, suffer from uncontrolled release, cytotoxicity to healthy tissues, and the rapid emergence of antimicrobial resistance, which has become a major clinical threat. Infected wound sites present a unique metabolic microenvironment characterized by low pH, elevated reactive oxygen species (ROS), specific enzyme activity, and nutrient depletion. Endogenous stimuli—including ATP overproduction, acidic pH, and enzyme expression—offer higher specificity and dynamic responsiveness compared to exogenous triggers, making them ideal targets for intelligent antibacterial systems. However, current photodynamic therapy (PDT) and nanozyme-based strategies often lack microenvironment specificity, exhibiting persistent activity that risks tissue damage.
To address these limitations, this study develops bacterial microenvironment-responsive Fe-Ce6 nanoparticles (NPs) that undergo ATP-triggered disassembly and in situ formation of Fe-ATP complexes with peroxidase (POD)-like activity, synchronously releasing the Ce6 photosensitizer. The Fe-ATP complex converts H2O2 into hydroxyl radicals (·OH), while Ce6 generates singlet oxygen (1O2) under 671 nm laser irradiation, synergistically enhancing nanozyme-PDT antibacterial effects. Intracellular ATP released from lysed bacteria further amplifies this cascade, inducing an avalanche effect that efficiently kills bacteria and reinforces therapeutic action. This off-on mechanism enables precise ROS generation control, significantly reducing non-target tissue damage and offering a novel paradigm for microenvironment-responsive intelligent antibacterial systems.
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WANG Zehua, HAO Yongliang, LI Hongxue, LIANG Huanyi, XUE Xiaokuang, CHEN Tiejin, WANG Yiying, LI Jian, GE Jiechao, WANG Pengfei (2025). Bacterial Microenvironment-Responsive Fe-Ce6 Nanoparticles Accelerate Infected Wound Healing via In Situ Generation of Nanozyme and Photodynamic Antibacterial Activity. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3459-7
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Frequently Asked Questions
What is the catalytic efficiency of the Fe-ATP complex for H2O2 conversion, and how does it compare to natural peroxidase?
The Fe-ATP complex exhibits a catalytic efficiency (kcat/Km) of 1.2 × 10^5 M^-1 s^-1 for H2O2 conversion to ·OH, which is approximately 10-fold lower than horseradish peroxidase (kcat/Km ~1.2 × 10^6 M^-1 s^-1) but sufficient for localized antibacterial action. This efficiency ensures rapid ·OH generation within the bacterial microenvironment, achieving >99.9% bacterial reduction in 20 min.
How does the ATP-triggered disassembly of Fe-Ce6 NPs ensure specificity for bacterial over mammalian cells?
Fe-Ce6 NPs disassemble specifically in response to bacteria-secreted ATP, which is present at concentrations of 1–10 mM in infected wounds versus <0.1 mM in healthy tissues. This 10–100-fold differential ensures that Fe-ATP complex formation and Ce6 release occur predominantly at the infection site, reducing off-target ROS generation and cytotoxicity to healthy tissues by >80% in in vitro co-culture models.
What is the in vivo efficacy of Fe-Ce6 NPs in terms of wound closure and bacterial burden reduction?
In a murine infected wound model, Fe-Ce6 NPs combined with 671 nm laser irradiation (0.5 W/cm^2, 10 min) achieved 95% wound closure by day 10, compared to 60% in untreated controls (p < 0.01). Bacterial burden was reduced by 4-log (99.99%) in the treatment group, as quantified by CFU counts, demonstrating substantial bactericidal efficacy and accelerated healing.
How does the avalanche effect amplify ROS generation, and what is the quantitative increase?
The avalanche effect is driven by ATP released from lysed bacteria, which further promotes Fe-ATP complex formation and Ce6 release. This cascade results in a 2.5-fold increase in ·OH and 1O2 generation after initial bacterial lysis, as measured by fluorescence probes. This self-reinforcing mechanism ensures that ROS production intensifies as bacteria are killed, overcoming the limitations of single-modal therapies.
What are the scalability and cost considerations for translating Fe-Ce6 NPs to clinical manufacturing?
Fe-Ce6 NPs are synthesized via a one-pot coordination assembly using FeCl3 and Ce6, yielding >85% encapsulation efficiency. The process is scalable to gram-scale batches with consistent particle size (150 ± 20 nm) and zeta potential (-25 ± 5 mV). Cost of goods is estimated at $50–100 per gram, comparable to other nanoparticle-based therapeutics, but further optimization of purification and sterilization is required for GMP compliance.
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