Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Live and in Color

29.10.2012
Fluorescent pH-sensitive nanoparticles indicate bacterial growth

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
Otto S. Wolfbeis is Director of the Institute for Analytical Chemistry, Chemo- and Biosensors at the University of Regensburg. His research is concentrated in the area of optical sensors for fundamental indicators such as pH value, oxygen, and glucose.

Author: Otto S. Wolfbeis, University of Regensburg (Germany), http://www.wolfbeis.de

Title: 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
Further information:
http://pressroom.angewandte.org.

Further reports about: 3-D Petri dish Angewandte Chemie Color test digital camera

More articles from Life Sciences:

nachricht Topologische Quantenchemie
21.07.2017 | Max-Planck-Institut für Chemische Physik fester Stoffe

nachricht Topological Quantum Chemistry
21.07.2017 | Max-Planck-Institut für Chemische Physik fester Stoffe

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Manipulating Electron Spins Without Loss of Information

Physicists have developed a new technique that uses electrical voltages to control the electron spin on a chip. The newly-developed method provides protection from spin decay, meaning that the contained information can be maintained and transmitted over comparatively large distances, as has been demonstrated by a team from the University of Basel’s Department of Physics and the Swiss Nanoscience Institute. The results have been published in Physical Review X.

For several years, researchers have been trying to use the spin of an electron to store and transmit information. The spin of each electron is always coupled...

Im Focus: The proton precisely weighted

What is the mass of a proton? Scientists from Germany and Japan successfully did an important step towards the most exact knowledge of this fundamental constant. By means of precision measurements on a single proton, they could improve the precision by a factor of three and also correct the existing value.

To determine the mass of a single proton still more accurate – a group of physicists led by Klaus Blaum and Sven Sturm of the Max Planck Institute for Nuclear...

Im Focus: On the way to a biological alternative

A bacterial enzyme enables reactions that open up alternatives to key industrial chemical processes

The research team of Prof. Dr. Oliver Einsle at the University of Freiburg's Institute of Biochemistry has long been exploring the functioning of nitrogenase....

Im Focus: The 1 trillion tonne iceberg

Larsen C Ice Shelf rift finally breaks through

A one trillion tonne iceberg - one of the biggest ever recorded -- has calved away from the Larsen C Ice Shelf in Antarctica, after a rift in the ice,...

Im Focus: Laser-cooled ions contribute to better understanding of friction

Physics supports biology: Researchers from PTB have developed a model system to investigate friction phenomena with atomic precision

Friction: what you want from car brakes, otherwise rather a nuisance. In any case, it is useful to know as precisely as possible how friction phenomena arise –...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Closing the Sustainability Circle: Protection of Food with Biobased Materials

21.07.2017 | Event News

»We are bringing Additive Manufacturing to SMEs«

19.07.2017 | Event News

The technology with a feel for feelings

12.07.2017 | Event News

 
Latest News

Vortex photons from electrons in circular motion

21.07.2017 | Physics and Astronomy

Topologische Quantenchemie

21.07.2017 | Life Sciences

Pulses of electrons manipulate nanomagnets and store information

21.07.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>