Phosphonium-Substituted Conjugated Polyelectrolytes Display Efficient Visible-Light-Induced Antibacterial Activity

Area of Science:

• Materials Science
• Photochemistry
• Microbiology

Background:

• Conjugated polyelectrolytes (CPEs) are polymers with unique electronic and optical properties.
• Phosphonium-containing compounds can exhibit antimicrobial properties.
• Photosensitization leading to reactive oxygen species (ROS) is a known antibacterial mechanism.

Purpose of the Study:

• To synthesize and characterize phosphonium-substituted conjugated polyelectrolytes (CPEs).
• To evaluate the in vitro antibacterial activity of these CPEs against Gram-negative and Gram-positive bacteria.
• To investigate the mechanisms behind both light-activated and dark antibacterial activity.

Main Methods:

• Synthesis of poly(phenylene ethynylene) (PPE) based CPEs with varying phosphonium side-chain lengths.
• In vitro antibacterial assays using Escherichia coli and Staphylococcus aureus.
• Exposure to dark and illumination conditions (blue LED) with varying CPE concentrations.
• Colony forming unit (CFU) reduction and serial dilution plating to quantify bacterial inactivation.

Main Results:

• CPEs demonstrated significant light-activated antibacterial activity, achieving >99% CFU reduction against both E. coli and S. aureus at low concentrations (≤20 μM) under illumination.
• Dark activity was observed, particularly against S. aureus, correlating with CPE hydrophobicity and side-chain length.
• Light-activated activity was linked to ROS generation, while dark activity was attributed to bacterial membrane disruption.
• A >5-log kill of E. coli was achieved within 15 minutes of blue light exposure.

Conclusions:

• Phosphonium-substituted CPEs are effective light-activated antibacterial agents.
• The antibacterial efficacy is tunable by modifying CPE side-chain length.
• These materials offer a promising platform for photodynamic antimicrobial therapies.