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
Fingerprint' technique spots frog populations at risk from pollution
27.03.2017 | Lancaster University
Parallel computation provides deeper insight into brain function
27.03.2017 | Okinawa Institute of Science and Technology (OIST) Graduate University
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
27.03.2017 | Earth Sciences
27.03.2017 | Life Sciences
27.03.2017 | Life Sciences