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When a nanoparticle enters into plasma, a discontinuous signal occurs. Signal intensity correlates to particle size.

© Fraunhofer IGB

Abstract:
Loads of cosmetics like sunscreen lotions contain titanium dioxide. These nanoparticles are contentious. Experts suspect they may have harmful effects on people and the environment. But it is difficult to prove that the particles are in the lotions. Using a method developed by Fraunhofer researchers, the particles can now be calculated.

Proving nanoparticles in sunscreen products

Muenchen, Germany | Posted on August 4th, 2015

Cosmetics increasingly contain nanoparticles. One especially sensitive issue is the use of the miniscule particles in cosmetics, since the consumer comes into direct contact with the products. Sunscreen lotions for example have nanoparticles of titanium oxide. They provide UV protection: like a film made of infinite tiny mirrors, they are applied to the skin and reflect UV rays. But these tiny particles are controversial. They can penetrate the skin if there is an injury, and trigger an inflammatory reaction. Its use in spray-on sunscreens is also problematic. Scientists fear that the particles could have a detrimental effect on the lungs when inhaled. Even the effect on the environment has not yet been adequately researched. Studies indicate that the titanium oxide which has seeped into public beaches through sunscreens can endanger environmental balance. Therefore, a labeling requirement has been in force since July 2013, based on an EU Directive on cosmetics and body care products. If nano-sized ingredients are used in a product, the manufacturer must make this fact clear by adding “nano-” to the listed ingredient name. Due to requirements imposed by the legislature, the need for analysis methods is huge.

Determining particle sizes down to the tiniest scale

Today’s electron microscope imaging processes, such as transmission-electron microscopy or scanning electron microscopy, are based on the properties of light dispersion. They are used to detect all particles present. They do not differentiate between a cell, a nanoparticle – or a piece of lint. These methods are ideally suited for the study of surface properties and shapes.

“The light diffusion process and microscopy are not selective enough for a lot of studies, including toxicological examinations,” says Gabriele Beck-Schwadorf, scientist at the Fraunhofer Institute for Interfacial Engineering and Thin Films IGB in Stuttgart. The group manager and her team have advanced and refined an existing measurement method in a way that allows them to determine titanium nanoparticles within complex media consisting of several different components that are highly sensitive and delicate. Researchers measure individual particles by single particle, inductively coupled plasma mass spectroscopy (or SP-ICP-MS). “With this method, I determine mass. Titanium has an atomic mass of 48 AMUs (atomic mass units). If I set the spectrometer to that, then I can target the measurement of titanium,” explains Katrin Sommer, food chemist at IGB.

With particle measurement, a suspension is sprayed into the plasma that contains both large and small particles in non-homogeneous distribution. The suspension has to be thinned out sharply so that one titanium dioxide particle after another can be detected and analyzed. Ions are formed out of these particles in hot plasma of about 7,000 Kelvins. They get to the spectrometer’s detector as an ion cloud, and are counted within the briefest measurement time of about three milliseconds. Signal intensity correlates to particle size. “We convert the intensity into nanometers. At the same time, we count particle signals, from which we calculate particle concentration with up to ten percent accuracy. We can establish exactly how many particles are of a specific size,” says Sommers, explaining the procedure.

It was IGB scientists who originally developed the methods for measuring titanium oxide nanoparticles in wastewater. “But the process is generally suitable for complex media, and can also be applied to sunscreen lotions,” the researcher indicates. A unique feature of this approach: the IGB team performs the data analysis and data processing without specialized software. “We have statistically evaluated the raw data using a standard computer program, and thus can work irrespective of the producer. Compared to existing methods, SP-ICP-MS involves a rapid process that uses detection limits that extend down to the ultra-trace amount scale below ppm.” For example, one sample of just a few milliliters can be examined in about six minutes.

Cosmetics makers, nanotechnology businesses, and consumers can benefit from the particle analysis for quality assurance of sun protection and body care products, but also use them for analyzing water, drinking water, and food. The researchers are planning to measure other nanoparticles in the future as well, such as silica dioxide. One can only determine whether a product contains silica dioxide through complex measurements. In order to establish the presence of nanoparticles, one must first determine their size or size distribution. Based on the EU’s definition, declaration requirements apply to a nanomaterial if at least 50 percent of the contained particles are of a size measuring between 1 and 100 nanometers (nm). Previous analysis methods are hitting their limits here. These make it possible to establish particle sizes only in pure solutions. They are not suited for analysis of complex media that one finds in modern cosmetics. In addition, nanoparticles with various chemical properties cannot be differentiated from each other this way.

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About Fraunhofer-Gesellschaft
The Fraunhofer-Gesellschaft is the leading organization for institutes of applied research in Europe, undertaking contract research on behalf of industry, the service sector and the government. Commissioned by customers in industry, it provides rapid, economical and immediately applicable solutions to technical and organizational problems. Within the framework of the European Union's technology programs, the Fraunhofer-Gesellschaft is actively involved in industrial consortiums which seek technical solutions to improve the competitiveness of European industry.

The Fraunhofer-Gesellschaft

Research of practical utility lies at the heart of all activities pursued by the Fraunhofer-Gesellschaft. Founded in 1949, the research organization undertakes applied research that drives economic development and serves the wider benefit of society. Its services are solicited by customers and contractual partners in industry, the service sector and public administration. The organization also accepts commissions from German federal and Laender ministries and government departments to participate in future-oriented research projects with the aim of finding innovative solutions to issues concerning the industrial economy and society in general.

Applied research has a knock-on effect that extends beyond the direct benefits perceived by the customer: Through their research and development work, the Fraunhofer Institutes help to reinforce the competitive strength of the economy in their local region, and throughout Germany and Europe. They do so by promoting innovation, accelerating technological progress, improving the acceptance of new technologies, and not least by disseminating their knowledge and helping to train the urgently needed future generation of scientists and engineers.

As an employer, the Fraunhofer-Gesellschaft offers its staff the opportunity to develop the professional and personal skills that will allow them to take up positions of responsibility within their institute, in other scientific domains, in industry and in society. Students working at the Fraunhofer Institutes have excellent prospects of starting and developing a career in industry by virtue of the practical training and experience they have acquired.

At present, the Fraunhofer-Gesellschaft maintains more than 80 research units, including 56 Fraunhofer Institutes, at 40 different locations in Germany. The majority of the 12,500 staff are qualified scientists and engineers, who work with an annual research budget of €1.2 billion. Of this sum, more than €1 billion is generated through contract research. Two thirds of the Fraunhofer-Gesellschaft’s contract research revenue is derived from contracts with industry and from publicly financed research projects. Only one third is contributed by the German federal and Laender governments in the form of institutional funding, enabling the institutes to work ahead on solutions to problems that will not become acutely relevant to industry and society until five or ten years from now.

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Contacts:
Claudia Vorbeck
Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB
+49 711 970-4031

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