Detecting nanoparticles in minute quantities

Nanomaterials keep our mattresses clean, putty cracks in our teeth, keep the egg in the pan from burning, and make our food more durable. A few billionths of a meter in size, the particles are incorporated into a wide range of consumer products. To date, however, it is largely unknown how these materials affect the environment and in what quantities and forms they are present. "While there are numerous laboratory studies that have examined the effect of nanomaterials on human and animal cells. So far, however, it has not been possible to detect the very small quantities in environmental samples," says Dr. Yvonne Kohl of the Fraunhofer Institute for Biomedical Engineering IBMT in Sulzbach, Saarland.

1 millionth milligram per liter

This is exactly the goal of the project NanoEnvironment. As a first major milestone, the interdisciplinary team of eco- and human toxicologists, physicists, chemists and biologists has succeeded in developing a method that detects nanomaterials in different environmental samples, such as river water, animal tissue or human urine and blood, in a concentration range of nanograms per liter (ppb - parts per billion). This corresponds to half a sugar cube in the water volume of 1,000 sports swimming pools.

With the new method, it is possible to detect not only many nanomaterials in clear liquids, as was previously the case, but also very few particles in complex mixtures of substances, such as human blood or soil samples. The approach is based on field-flow fractionation (FFF), which makes it possible to separate complex, heterogeneous mixtures of liquids and particles into their individual components, sorting the solid components according to their size. This is achieved by the interaction of a controlled liquid flow and a physical separation field acting perpendicularly on the flowing suspension.

For detection to succeed, the environmental samples must be prepared accordingly. The IBMT team from the Bioprocesses & Bioanalytics department made river water, human urine and fish tissue fit for the FFF instrument. "We prepare the samples with special enzymes. During this process, however, the nanomaterials must not be destroyed or altered. Only then can we detect the real quantities and forms of nanomaterials in the environment," Kohl explains.

The scientists are experts in particular when it comes to holding, processing and storing human tissue samples. Since January 2012, the IBMT has been operating the "Federal Environmental Specimen Bank (UPB) - Human Specimens" on behalf of the Federal Environment Agency (UBA). Every year, the research institute collects blood and urine samples from 120 volunteers at four locations in Germany. The individual samples are a valuable tool for tracking temporal trends in human exposure to pollutants. "For the NanoUmwelt project, additional blood and urine were donated, cold-stored at the IBMT and used to develop the new detection method," says Dr. Dominik Lermen, head of the Biomonitoring & Cryobanks working group at the IBMT. After approval by the UBA, some of the human samples from the UPB archive could also be examined using the new method.

New cell culture models developed

Nanomaterials can enter the environment through a variety of pathways, including wastewater, and are thought to be taken up by humans and animals through biological barriers, such as the lungs or intestines. The project team is recreating these processes in the Petri dish to understand how nanomaterials are transported across these barriers. "This is a very complex process involving a wide variety of cells and tissue layers," Kohl explains.

The researchers recreate the processes as realistically as possible. To do this, for example, they measure the electrical fluxes within the barriers to determine their functionality or use artificial clouds of mist to simulate the interaction of the lungs with the air. In the first phase of the NanoEnvironment project, the IBMT team was able to develop various cell culture models for the transport of nanoparticles across biological barriers. In the process, the IBMT collaborated with the Fraunhofer Institute for Molecular Biology and Applied Ecology IME, which developed a model from pluripotent stem cells to study cardiotoxicity. The Swiss project partner Empa realized a placental barrier model to study nanomaterial transport between mother and child.

In the next step, the cooperation partners want to use the method to measure concentrations of nanoparticles in various environmental samples and analyze the values determined in order to better assess the behavior of nanomaterials in the environment and their potential danger to humans, animals and the environment. "Our next goal is to detect even smaller amounts of particles," Kohl says. The scientists plan to use special filters to remove interfering elements from the environmental samples and to develop new processing techniques.

(Fraunhofer IBMT)