Ethel Koranteng1 Alexander MacRobert2 Elaine Allan3 Ivan Parkin4

1, University College London, London, , United Kingdom
2, University College London, London, , United Kingdom
3, University College London, London, , United Kingdom
4, University College London, London, , United Kingdom

Antimicrobial resistance (AMR) occurs when microorganisms change in ways that render them unresponsive to previously effective medications. AMR is especially amplified in the hospital where excessive and often unnecessary use of antibiotics increases selective pressure in bacterial populations, allowing bacteria that can acquire resistance to thrive. This has led to a rise of hospital-acquired infections (HAIs) that are progressively more challenging to treat and increase morbidity and mortality as well as costing billions in healthcare costs for patients and healthcare systems worldwide.

Bacterial contamination on hospital touch surfaces such as door handles, computer keyboards and telephones is extremely common, facilitating the spread of HAIs. One strategy to reduce HAIs is the use of antimicrobial surfaces containing quantum dots (QDs) – highly fluorescent inorganic semiconducting nanoparticles usually ranging from 2 to 10 nm in diameter – which exhibit antibacterial activity through light-activated generation of cytotoxic reactive oxygen species (ROS).

In this interdisciplinary project, new commercial non-toxic cadmium-free QD nanoparticles are incorporated into polymer along with a clinically approved photosensitising dye, crystal violet (CV) using a simple, non-covalent and up-scalable ‘swell-encapsulation-shrink technique’. The combination of QDs and CV dye enhances antibacterial activity by boosting ROS production via Forster Resonance Energy Transfer (FRET). Moreover, unlike dyes used on their own, QDs absorb energy broadly in the visible range, enabling activation of QD-CV materials by ambient lighting, much safer than UV radiation.

The antibacterial activity of QD-CV samples was tested against Staphylococcus aureus and Escherichia coli as representative Gram-positive and Gram-negative bacteria under dark and light conditions. QD-CV samples displayed potent antibacterial activity, resulting in complete kill of a laboratory strain of Staphylococcus aureus after 1 hour irradiation at 6000 lux light intensity and 99.99% (4 log) reduction of a laboratory strain of Escherichia coli. QD-CV samples were also effective against clinical strains of bacteria, inducing a 99.97% (3.5 log) reduction in MRSA and 99.85% reduction (2.8 log) in E.coli 1030, a carbapenemase-expressing multi-drug resistant strain of Escherichia coli.

This work demonstrates that the effectiveness of QD-photosensitiser-incorporated polymer surfaces and offer a viable alternative to reduce contamination of frequently touched surfaces in hospital wards thus potentially decreasing the risk of hospital-acquired infections.