Animal testing is an area that elicits strong feelings on both sides of the argument for and against the practice. Supporters like the British Royal Society argue that virtually every medical breakthrough of the 20th century involved the use of animals in some way, while opponents say that it is not only cruel, but actually impedes medical progress by using misleading animal models. Whatever side of the argument researchers fall on, most would likely use an alternative to animal testing if it existed. And an alternative that reduces the need for animal testing is just what Fraunhofer researchers hope their new sensor nanoparticles will be.

Instead of exposing animals to chemicals to study their effects and potential risks, the team of researchers at the Fraunhofer Research Institution for Modular Solid State Technologies (EMFT) in Munich have a developed a nanosensor alternative. As Dr. Jennifer Schmidt of the EMFT explains, "What we do is take living cells, which were isolated from human and animal tissue and grown in cell cultures, and expose them to the substance under investigation."

The nanosensors are used to detect a molecule known as adenosine triphosphate (ATP). Often called the "molecular unit of currency" of intracellular energy transfer, ATP is responsible for transporting chemical energy within cells for metabolism. As healthy cells store energy in the form of ATP, high levels of ATP indicate high levels of metabolic activity in cells, while cells that are severely damaged become less active, store less energy and produce less ATP.

"Our nanosensors allow us to detect adenosine triphosphate and determine the state of health of cells. This makes it possible to assess the cell-damaging effects of medical compounds or chemicals," says Schmidt.

To register the ATP, the nanoparticles are given two fluorescent dyes - a green indicator dye that is sensitive to ATP, and a red reference dye that doesn't change color. When the particles are introduced to living cells and observed under a fluorescence microscope, the degree to which the particles light up indicates the quantity of ATP present. A more yellow overlay image indicates active cells, while a redder overlay image would indicate that the health of the cells is impaired.

"We could in future use cancer cells to test the effectiveness of newly developed chemotherapy agents. If the nanosensors detect a low concentration of ATP in the cells, we'll know that the new treatment is either inhibiting tumor cell growth or even killing them," says Schmidt. "The most promising agents could then be studied further."

The researchers say their nanoparticles are not poisonous to cells and can easily pass through cell membranes. They can also be directed to particular points where the effect of the test substance is of most interest. Through the development of nanosensors that can determine concentrations of oxygen and toxic amines, the researchers have also adapted the technology to testing the quality of meat and say it could also be used in other applications.

Because the nanoparticle testing procedure must be approved by regulatory authorities before it can be applied, the Fraunhofer researchers expect a long wait before it gets the thumbs up from the various official bodies and can start to reduce the number of tests involving laboratory animals.

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