Antimicrobial resistance is a serious threat to global health, a phenomenon that is largely driven by incorrect treatment regimens, which result in misuse and overuse of antibiotics. Therefore, it is important to develop rapid and cheap ways of detecting bacteria, along with their sensitivity or resistance to antibiotics. This would allow rapid diagnosis of infections, tailored prescription of drugs and, in turn, a more informed and sustainable use of antibiotics.
Sense-and-treat
In response to these demands, a team of researchers from the Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, has developed a paper-based adhesive plaster, or band-aid, based on a “sense and treat” approach. The plaster senses the presence of bacteria by changing its colour and releases antibiotics when necessary. In addition, the paper is able to distinguish between certain drug-susceptible and drug-resistant bacteria, therefore informing the best disinfection strategy (ACS Cent. Sci. 10.1021/acscentsci.9b01104).
The plaster works like a traffic light. It appears green under normal conditions, while it turns yellow in the presence of drug-sensitive bacteria and automatically releases antibiotics to kill them. If the bacteria are drug-resistant, the paper becomes red and photodynamic therapy (PDT) can be used instead. PDT is performed by shining 628 nm light onto the plaster, which induces the production of reactive oxygen species that kill or weaken the resistant bacteria.
Ad-hoc chemistry
The plaster exploits chemical compounds that change colour in the presence of bacteria. In particular, the material is soaked in bromothymol blue, a pH indicator that turns from green to yellow when exposed to the acidic environment created by bacterial metabolism. The paper also contains a pH-sensitive metal–organic framework, a compound that acts as a cage containing antibiotic molecules. Upon increased acidity, the framework breaks open and the encapsulated antibiotic is released.
A wide class of resistant bacteria produce β-lactamase, an enzyme that destroys certain types of antibiotic molecules. In response to this, the plaster is also equipped with nitrocefin, an antibiotic that shows a distinct colour change from yellow to red when interacting with β-lactamase, hence signalling the presence of drug-resistant bacteria and the need for a therapy other than antibiotics.
Based on these principles, the researchers have shown that the plaster accelerates wound healing in mice infected with both sensitive and resistant bacteria. They monitored the status of the wound over three days, and clearly observed improved tissue regeneration following the disinfecting action of either antibiotics or PDT.
The team also demonstrated the potential of the paper device in a fruit preservation model, in which it was attached onto an infected tomato that successfully recovered after three days of sensing and treatment.
The future of diagnosis and treatment
The team’s novel adhesive plaster offers great potential for the future of diagnosing and treating wound infections. It is cheap, easy to use, and effective against certain types of bacterial infections. Extending the method to practical and point-of-care applications will be the next challenge towards widespread use. Technologies like this could contribute significantly to the fight against antimicrobial resistance.
