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
Scientists discover new 'architecture' in corn
21.01.2019 | Louisiana State University
Nuclear actin filaments determine T helper cell function
21.01.2019 | Universitätsklinikum Heidelberg
The scientific and political community alike stress the importance of German Antarctic research
Joint Press Release from the BMBF and AWI
The Antarctic is a frigid continent south of the Antarctic Circle, where researchers are the only inhabitants. Despite the hostile conditions, here the Alfred...
World first experiments on sensor that may revolutionise everything from medical devices to unmanned vehicles
The new sensor - capable of detecting vibrations of living cells - may revolutionise everything from medical devices to unmanned vehicles.
Dead and alive at the same time? Researchers at the Max Planck Institute of Quantum Optics have implemented Erwin Schrödinger’s paradoxical gedanken experiment employing an entangled atom-light state.
In 1935 Erwin Schrödinger formulated a thought experiment designed to capture the paradoxical nature of quantum physics. The crucial element of this gedanken...
Cellulose obtained from wood has amazing material properties. Empa researchers are now equipping the biodegradable material with additional functionalities to produce implants for cartilage diseases using 3D printing.
It all starts with an ear. Empa researcher Michael Hausmann removes the object shaped like a human ear from the 3D printer and explains:
The phenomenon of so-called superlubricity is known, but so far the explanation at the atomic level has been missing: for example, how does extremely low friction occur in bearings? Researchers from the Fraunhofer Institutes IWM and IWS jointly deciphered a universal mechanism of superlubricity for certain diamond-like carbon layers in combination with organic lubricants. Based on this knowledge, it is now possible to formulate design rules for supra lubricating layer-lubricant combinations. The results are presented in an article in Nature Communications, volume 10.
One of the most important prerequisites for sustainable and environmentally friendly mobility is minimizing friction. Research and industry have been dedicated...
16.01.2019 | Event News
14.01.2019 | Event News
12.12.2018 | Event News
21.01.2019 | Life Sciences
21.01.2019 | Physics and Astronomy
21.01.2019 | Life Sciences