Photo of biocidal and antifouling activity of AgNP/MOF composite (AgNPs@nanoMOF).
Photo of biocidal and antifouling activity of AgNP/MOF composite (AgNPs@nanoMOF).

A new composite coating based on a porous hybrid material containing silver nanoparticles could help stop the spread of infectious diseases from bacterial contamination of surgical devices and frequently touched surfaces such as door handles, buttons, and hand rails. Currently, around 80% of hospital-acquired infections arise communities of bacteria known as biofilms – particularly Staphylococcus aureus, which is commonly found in nasal passages and on the skin.

“The formation of bacterial biofilm on surfaces occurs naturally and its inhibition and treatment to limit the propagation of infectious diseases is still an unsolved challenge,” explains first author of the study, Ana Arenas-Vivo of the IMDEA Energy Institute in Spain. “Traditionally, antibiotics have been used to mitigate the formation of these invasive colonies but the growing appearance of multi-drug resistant strains has obliged researchers to find solutions elsewhere.”

The researchers from IMDEA Energy and the University of Alcalá have brought together three recognized approaches to create a single composite material with greatly improved antibacterial properties. A porous crystalline material, know as a metal-organic framework (MOF), which consists of inorganic units held together by organic linking molecules, forms the basis of the composite. The researchers chose a nontoxic titanium-based MOF, with unexpected biocidal properties, and impregnated it with silver nanoparticles (AgNPs), which have widely recognized antibiotic properties. While both material components show intrinsic biocidal effects, the researchers went one step further and subjected the composite to UV light, which inhibits bacterial growth and detaches the biofilm from the surface.

“The interaction between the AgNPs and the nanoscale-MOF structure promotes an intrinsic biocidal character, which is even more enhanced when the composite is irradiated,” says Arenas-Vivo.

The researchers believe that the enhanced biocidal effect arises because UV irradiation promotes the formation of reactive oxygen species, such as HO, O2•-, and HO2, which disrupt biofilm formation, leading to bacterial death and detachment from the surface.

“This is the first MOF-based composite that advantageously combines both bactericidal (>90% of remaining bacteria are nonviable) and antifouling (anti-adherent) properties (80% of bacteria detached compared to control),” points out Arenas-Vivo.

As a proof-of-concept, the researchers coated glass slides with the AgNP/MOF composite and showed that it remains stable when exposed to bacterial solutions and continues to release antibacterial Ag+ and Ti+ ions over an extended period of 14 days.

“Our active coating enables the mitigation of biofilms and their treatment by simple irradiation over long time periods,” says Arenas-Vivo. “This photocatalytic self-cleaning could inactivate infectious agents on high-touch surfaces, breaking the link between contaminated surfaces and contact transmission.”

The team now plans to test the abilities of the AgNP/MOF coating to inhibit biofilm formation under continuous contaminated water flow.

Arenas-Vivo et al., Acta Biomaterialia (2019),