Nanoscale Horizons blog

Chronic wounds are considered a major healthcare problem all over the world. Long-term infections and/or suppressed immune responses may cause chronic wounds with slower healing, resulting in increased mortality. Although antibiotics, skin disinfectants, and hydrogels are currently being used to combat microbial pathogenesis, they still have some significant limitations when used in clinical wound healing. Therefore, researchers have been exploring alternative approaches, such as combining antimicrobial, antioxidant, and anti-inflammatory agents for advanced chronic wound therapy.

Recently, nanomaterial-based antimicrobials have gained popularity thanks to catalytic and near-infrared (NIR) irradiation treatments, which induce controlled oxidative stress (photodynamic and catalytic therapies) and hyperthermia (photothermal therapies) to eradicate bacteria. However, little research into nanomaterial-based antimicrobial activity against biofilms and chronic wound healing in vivo has previously been reported.

Fig. 1 An overview of the properties of CuS/Qu–CNGs and their role in wound healing. Reproduced from DOI: 10.1039/D3NH00275F with permission from the Royal Society of Chemistry.

In this regard, an NIR-triggered multifunctional quercetin carbonized nanogel embedded with copper sulfide nanoclusters (CuS/Qu-CNG) was reported by Nain et al. for advanced therapy of chronic wounds. Polymerization and mild carbonation procedures were used to prepare quercetin carbonized nanogels (Qu-CNGs), which were subsequently used as templates to grow CuS in situ forming CuS/Qu-CNGs. The resulting CuS/Qu–CNGs are photoreactive and contain antioxidant and catalytic properties (oxidase- and peroxidase-like activities). As a result of their photo-responsive properties, CuS/Qu-CNGs significantly amplified their antimicrobial activity when exposed to NIR-II light. A CuS/Qu–CNGs MIC₉₀ value of 6–9 mg mL^-1 is ~125-fold lower than Qu or Qu–CNGs under NIR-II irradiation and was further improved by ~30-fold (ca. 0.2 mg mL^-1) in the presence of H₂O₂. Besides, CuS/Qu-CNGs demonstrated exceptional penetration ability, eliminating MRSA biofilms caused by diabetic wounds in diabetic mice. By suppressing pro-inflammatory cytokines (IL-1β) and boosting anti-inflammatory cytokines (IL-10 and TGF-β1), CuS/Qu-CNGs significantly accelerated wound healing by promoting angiogenesis, epithelialization and collagen synthesis. Finally, CuS/Qu–CNGs showed superior in vivo efficacy in treating bacterial infections and enhancing wound healing in diabetic mice.

In summary, a “Three in One” multifunctional CuS/Qu-CNGs with excellent antimicrobial/antioxidative/anti-inflammatory properties demonstrate great potential in treating bacterial infections and promoting chronic wound healing. This work is expected to provide new solutions for wound treatment complicated by microbial pathogenesis.

To find out more, please read:

NIR-activated quercetin-based nanogels embedded with CuS nanoclusters for the treatment of drug-resistant biofilms and accelerated chronic wound healing
Amit Nain, Yu-Ting Tseng, Akash Gupta, Yu-Feng Lin, Sangili Arumugam, Yu-Fen Huang, Chih-Ching Huang and Huan-Tsung Chang
Nanoscale Horiz., 2023, 8, 1652-1664

About the blogger

Jiangjiexing Wu is an Associate Professor at Tianjin University and a member of the Nanoscale Horizons Community Board. Dr Wu’s research focuses on the rational design and synthesis of functional nanomaterials (such as nanozymes) for analytical, biomedical, and environmental applications.

Recycling CO₂ molecules through photocatalysis represents an innovative technology to mitigate the emission of CO₂ gas. The deliberate introduction of defects into a photocatalyst plays a crucial role in optimizing photocatalytic performance, since the defects regulate the electronic structure, fine-tune selectivity by enhancing catalytic activity, and reduce the activation barrier of the catalyst.

A team of researchers based in Australia have recently developed a photocatalytic system for CO production by CO₂ reduction. In this study, defect-rich g-C₃N₄ serves as a semiconducting substrate, and it was further loaded with Ag nanoparticles (NPs) to act as a plasmonic source, resulting in the creation of the g-C₃N₄-Ag photocatalyst. The defects within the g-C₃N₄ were known as the active sites that enhance the efficiency of photocatalytic CO₂ conversion. In addition, these defects are strategically positioned alongside the loaded Ag NPs, which improves the effectiveness of injected hot electrons from the Ag NPs, thereby synergistically enhancing the activity of photocatalytic CO₂ reduction.

In the experiments involving defect-rich g-C₃N₄, different photodeposition times, including 10 minutes, 1 hour, 3 hours, and 5 hours, were performed to load Ag particles, denoted the as-preared photocatalyst as g-C₃N₄-Ag 10m, 1h, 3h, and 5h, respectively. These variants were evaluated for their photocatalytic performance in CO production via CO₂ reduction (Fig. 1a). The optimal performance was achieved with g-C₃N₄-Ag 1h, and the production of CO was confirmed through isotopic experiments (Fig. 1b). The g-C₃N₄-Ag photocatalysts were characterized using scanning transmission electron microscopy, as typical image is presented in Fig. 1c and the corresponding elemental mapping were presented in Fig. 1d to 1g.

Fig 1. (a) CO production rate based on various g-C3N4 based photocatalysts. (b) Isotope labelling experiments tested under 13CO2 and 12CO2, and the mass spectrometry signals at m/z = 28 and m/z = 29 are 13CO and 12CO, respectively. (c) STEM dark field image and (d)–(g) elemental mapping of g-C3N4-Ag 1h catalyst. Scale bar: 300 nm. Reproduced from DOI: 10.1039/D3NH00348E with permission from the Royal Society of Chemistry.

To elucidate the mechanism behind the defect engineering scenario, Ag NPs were initially loaded onto g-C₃N₄ via photodeposition. Due to the electron-rich environment of the point defects on g-C₃N₄, Ag⁺ ions selectively grow on these defect sites. The resulting g-C₃N₄-Ag composite was subsequently annealed. During this process, the new defects formed on the g-C₃N₄ substrate owing to the strain induced by the differing thermal expansion rates between the Ag and g-C₃N₄. These new defects were found to be located around the Ag NPs, representing a significant change in the pristine g-C₃N₄ following the introduction of Ag.

Furthermore, density functional theory (DFT) calculations were conducted to gain a deeper understanding of how the defects in g-C₃N₄ improve performance. Three models of photocatalysts were considered, including pristine g-C₃N₄, g-C₃N₄ with N vacancies, and N vacancies in g-C₃N₄ with O sites on the surface. In the models of pristine g-C₃N₄ and g-C₃N₄ with N vacancies, the formation of *COOH intermediates was identified as the rate-limiting step (RDS), and moreover, N vacancies in g-C₃N₄ were found to enhance the activity in this conversion (Fig 2a). For N vacancies in g-C3N4 with additional surface O sites (Fig. 2b), the initial reaction step favored the formation of *COOH intermediates from a thermodynamic perspective. Subsequently, the reduction of *COOH intermediates to *CO species occurred by reacting with protons, releasing H₂O molecules. In the case of O-enriched g-C₃N₄, this conversion became the RDS. DFT calculations indicated that the ΔG values for *COOH and *H to form *CO and H₂O at the C defect active sites were 0.96 eV, which determined the reaction rate (Fig. 2c). These results provide insight into the reasons behind the improved performance in CO production through CO₂ reduction.

Fig 2. Optimized configurations of reaction intermediates *COOH and *CO on the C atom and N vacancy active sites of (a) g-C3N4 with N vacancy and (b) N vacancies in g-C3N4 with O sites on the surface. (Red ball is oxygen atom, white ball is hydrogen atom, gray is carbon atom, and blue is nitrogen atom) (c) Gibbs free energy diagrams for photocatalytic CO2 reduction to CO on g-C3N4, g-C3N4 with N vacancy and O-occupied g-C3N4. Reproduced from DOI: 10.1039/D3NH00348E with permission from the Royal Society of Chemistry.

In summary, the deliberate introduction of active defects into g-C₃N₄ photocatalysts, strategically positioned near the plasmon centers of Ag NPs, optimizes the utilization efficiency of plasmonic hot electrons, resulting in an enhanced efficiency for CO₂ photoreduction. Importantly, this strategy has the potential for extension to various systems based on polymers, hard materials, and hybrid materials, offering promising applications that harness the functionalities of defects in a wide range of fields.

To find out more, please read the full article:

Defect engineering enhances plasmonic-hot electrons exploitation for CO₂ reduction over polymeric catalysts
Hang Yin, Zhehao Sun, Kaili Liu, Ary Anggara Wibowo, Julien Langley, Chao Zhang, Sandra E. Saji, Felipe Kremer, Dmitri Golberg, Hieu T. Nguyen, Nicholas Cox and Zongyou Yin
Nanoscale Horiz., 2023, Advance Article

About the blogger

Yuanxing Fang is a Professor at Fuzhou University, and a member of the Nanoscale Horizons Community Board. Prof. Fang’s research lab focuses on the synthesis of metal-free semiconductors for photoelectrochemical systems for energy and environmental applications, including water splitting, hydrogen peroxide synthesis, organic transformations and others.