Rotting foods are a serious risk to our health. The food industry is therefore correspondingly strict in its vigilance toward bacteria in products. The influence of production and storage conditions on the growth of pathogens must constantly be evaluated.
In the journal Angewandte Chemie, researchers from Regensburg, Germany have now introduced a new method for monitoring the growth of bacteria: The fluorescence of nanoparticles embedded in an agarose growth medium changes significantly when the pH value changes because of bacterial metabolism. This can be monitored in real time with a simple digital camera.
Xu-dong Wang, Robert J. Meier, and Otto S. Wolfbeis from the University of Regensburg have developed a truly simple, broadly applicable process for the production of nanosensors for this purpose. A biocompatible polymer with water-friendly (hydrophilic) and water-repellent (hydrophobic) domains is added to water. If the concentration is right, the polymer forms stable micelles with relatively hydrophobic cores and a more hydrophilic outer layer.
The researchers embedded two different fluorescent dyes in these micelles. The first is a hydrophobic fluorescein dye that gives of green light when excited by an LED, and is sensitive to changes in the pH value. The second dye exhibits red fluorescence that is independent of the pH value and thus acts as an internal reference. These nanosensors are mixed into a combination of agarose and nutrients commonly used for bacterial cultures. This mixture is poured into Petri dishes, where it forms a gel.
In the initial state, the pH is set so that the green dye does not fluoresce; only the red fluorescence of the reference can be seen. When a sample containing bacteria is added, they begin to multiply. Their metabolism causes the pH value of the medium to rise. As the pH value increases, the nanoparticles give off more green light, while the red fluorescence remains unchanged. The radiation can easily be detected with the red and green channels of modern digital cameras.
The changes in the ratio of green to red fluorescence over time is recorded. This reflects the growth of the bacteria.
The nanoparticles are nontoxic and do not leave the agarose gel, so they are not taken up by the bacteria. They thus do not disrupt the growth of the bacteria, unlike some other sensors. The measurements are straightforward: Because it is only necessary to evaluate the ratio of the green fluorescence to the red reference, fluctuations in detection have no effect. By using conventional Petri dishes instead of small-format microtiter plates and imaging procedures instead of pH electrodes, it is also possible to resolve the spatial distribution of bacterial growth.
In the future, these new sensors could be integrated into food packaging along with a barcode to indicate the freshness of the food.About the Author
Author: Otto S. Wolfbeis, University of Regensburg (Germany), http://www.wolfbeis.deTitle: Fluorescent pH-Sensitive Nanoparticles in an Agarose Matrix for Imaging of Bacterial Growth and Metabolism
Angewandte Chemie International Edition, Permalink to the article: http://dx.doi.org/10.1002/anie.201205715
Otto S. Wolfbeis | Angewandte Chemie
Could this protein protect people against coronary artery disease?
17.11.2017 | University of North Carolina Health Care
Microbial resident enables beetles to feed on a leafy diet
17.11.2017 | Max-Planck-Institut für chemische Ökologie
The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.
Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...
Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.
That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...
Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.
During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....
The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.
Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...
Pillared graphene would transfer heat better if the theoretical material had a few asymmetric junctions that caused wrinkles, according to Rice University...
15.11.2017 | Event News
15.11.2017 | Event News
30.10.2017 | Event News
17.11.2017 | Physics and Astronomy
17.11.2017 | Health and Medicine
17.11.2017 | Studies and Analyses