Rapid nanoparticle test for sepsis


June 01, 2023

(Nanowerk News) For Qun Ren, every minute counts. Researcher Empa and his team are currently developing a diagnostic procedure that can quickly detect life-threatening blood poisoning caused by staphylococcus bacteria. This is because staphylococcal sepsis is fatal in up to 40 percent of cases. Spherical bacterial infection may start as a localized skin disease or pneumonia. Once staphylococci invade the bloodstream during sepsis, severe complications can develop. Antibiotic-resistant staphylococci (yellow) are fought by white blood cells Antibiotic-resistant staphylococci (yellow) are fought by white blood cells (blue). Image: Electron microscopy (NIAID), digitally stained. (Image: Empa)

In such situations the pathogen must be identified as quickly as possible and appropriate antibiotics selected for treatment. This is critical for the survival of those affected, as Staphylococcus aureus strains can become insensitive to many antibiotics (see box).

“If bacteria in blood samples have to be cultured first for a diagnostic procedure, valuable time is lost,” explains Qun Ren, group leader from Empa’s Biointerfaces lab in St. gallen. Therefore, Qun Ren and his teammate Fei Pan together with researchers from ETH Zurich looked for a way to bypass the long intermediate step.

Fished out of blood

The team has developed a method using magnetic nanoparticles that can bind to staphylococci. Bacteria can thus be specifically detected via a magnetic field. In the next step, the sensitivity to antibiotics was analyzed using the chemiluminescence method. If resistant bacteria are present in the test tube, the sample emits light. Conversely, if the germs can be killed with antibiotics, the reaction vessel remains dark. “Overall, the sepsis test takes about three hours – compared to several days for the classic cultivation of a bacterial culture,” said Fei Pan. Magnetic nanoparticles (red) bind specifically to spherical bacteria (yellow) Magnetic nanoparticles (red) bind specifically to spherical bacteria (yellow) that are about 1 µm in size (digital color electron microscope). (Image: Empa)

Dangerous light

Another unpleasant representative of the bacterial kingdom is Pseudomonas aeruginosa. These rod-shaped bacteria can cause a variety of illnesses, including urinary tract infections, for example through a urinary catheter during a hospital stay. Such an infection can then develop into sepsis. And these pathogens are also often resistant to a number of antibiotics.

This is where another advantage of magnetic nanoparticles comes into play: The method can adapt to different types of bacteria, similar to a modular system. In this way, Empa researchers can develop fast “sepsis sensors” based on magnetic nanoparticles. In samples containing artificial urine, this method reliably identifies bacterial species and determines possible resistance to antibiotics through the chemiluminescence reaction.

So far, the researchers have evaluated their magnetic nanoparticle device for sepsis and urinary tract infections using laboratory samples. “In the next step, we want to validate the sepsis test together with our clinical partners by evaluating patient samples,” said Qun Ren. The magnetic nanoparticles bind to the bacteria in the urine sample and can be isolated via a magnetic field The magnetic nanoparticles bind to the bacteria in the urine sample and can be isolated via a magnetic field (top). If resistant Pseudomonas pathogens are present in the sample, this can be visualized via chemiluminescence. (Image: Empa)


F Pan, S Altenried, S Scheibler, I Rodriguez Fernandez, G Giovannini, Q Ren; Ultrafast Determination of Antimicrobial-Resistant Staphylococcus aureus Specifically Captured by Functionalized Magnetic Nanoclusters; ACS sensors (2022), doi: 10.1021/acssensors.2c01837

F Pan, S Altenried, S Scheibler, AHC Anthis, Q Ren; Specific capture of Pseudomonas aeruginosa for rapid detection of antimicrobial resistance in urinary tract infections; Biosensors and Bioelectronics (2022); doi: 10.1016/j.bios.2022.114962


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