# Lignin Nanoparticles Containing Cobalt‐Cyanine Complexes: Potential Multifunctional Platforms for Photoacoustic Imaging and Photothermal Treatment of Bacterial Biofilms in Chronic Wounds

## TL;DR

Researchers developed cobalt-cyanine lignin nanoparticles that can both image and treat bacterial biofilms in chronic wounds using light.

## Contribution

The novel contribution is the creation of CoPc-Lig nanoparticles combining photothermal therapy and antioxidant activity for biofilm treatment.

## Key findings

- CoPc-Lig nanoparticles show antioxidant activity by scavenging reactive oxygen species and inhibiting key enzymes in chronic wound pathophysiology.
- The nanoparticles are internalized into Staphylococcus aureus and Pseudomonas aeruginosa biofilms, enhancing antibacterial effects.
- Near-infrared light excitation of the nanoparticles produces a mild photothermal effect that reduces bacterial viability and disrupts biofilm integrity.

## Abstract

Chronic wounds (CWs) are characterized by persistent inflammation and bacterial biofilms, which hinder healing and contribute to antibiotic resistance. Therefore, innovative treatments with both anti‐inflammatory and antibiofilm properties are urgently needed. Here, cobalt phthalocyanine (CoPc), a photo‐excitable dye, is combined with polyphenolic lignin to develop CoPc‐Lig nanoparticles (NPs). These NPs demonstrate antioxidant activity by scavenging reactive oxygen species and inhibiting key enzymes implicated in CW pathophysiology. Moreover, they are internalized into Staphylococcus aureus and Pseudomonas aeruginosa biofilms, a critical feature for enhancing antibacterial effects. Upon near‐infrared light excitation, CoPc‐Lig NPs produce a thermal increase, which reduces bacterial viability and disrupts biofilm integrity. This mild photothermal effect is particularly advantageous in CW treatment, as excessive temperatures can damage newly formed tissue. Additionally, the NPs exhibit strong photoacoustic (PA) properties, enabling their use in PA imaging, an emerging non‐invasive technique for real‐time monitoring. The PA signal remains stable over time and is detected in ex vivo tissue phantoms. These findings highlight the potential of CoPc‐Lig NPs as a theragnostic platform for CW management, integrating antimicrobial cobalt, antioxidant polyphenols, and photo‐excitable phthalocyanines. Future studies will focus on optimizing photothermal treatment conditions and exploring synergies with debridement and antibacterial agents to enhance therapeutic outcomes.

CoPc is combined with a lignin‐based material to obtain NPs sensitive to NIR irradiation and capable of ROS scavenging. Through the NPs, mild photothermal therapy can be achieved to act against bacterial biofilms.