Detect The Smallest Traces Of Pollutants Reliably And Quickly

Materials researchers are developing reusable nanomaterial for ultra-sensitive analyses

Even small traces of pollutants in water or other liquids can be detected using spectroscopic analysis methods. For use in forensics, the security industry, the food industry or medical diagnostics, methods like theHowever, surface-enhanced Raman scattering (SERS) is still too expensive and not reliable enough. A research team from Materials Science at Kiel University (CAU) has now succeeded in increasing the performance of the method by a factor of 50. They developed a substrate with special nanostructures that significantly increases the sensitivity and the spatial and temporal resolution of the method. This leads to high-precision and fast results even in the trace range. In addition, the substrate can be reused, which significantly reduces the cost of the analysis. The research team's findings have been published in the renowned journal Small .

Substrate plays a crucial role
Raman spectroscopy - named after the Indian physicist and Nobel Prize winner Chandrasekhara Venkata Raman - is a method to determine the chemical composition of materials and thus also to detect harmful substances. For this purpose, a fabric sample is irradiated with a laser. Conclusions can be drawn about the properties of the material based on the so-called Raman signal that is thrown back. “The substrate, the base on which the sample of material to be analyzed lies, plays a decisive role here. Because there are interactions with the laser light that affect the Raman signal," explains Josiah Ngenev Shondo, doctoral student at the Chair of Composite Materials.

Researchers at the chair have now succeeded in producing a substrate from various materials with which the Raman signal is amplified by a factor of 50 compared to classic SERS methods. "This is more than has ever been reported for this method," says Prof. Oral Cenk Aktas. This increases the sensitivity of the method and its spatial and temporal resolution. In this way, even very small amounts of substances can be analyzed in a short time. After the analysis, the researchers decomposed the fabric sample with UV light. "The relatively expensive substrate is cleaned in this way and can be used several times for the first time - up to twenty times in our test," continues Aktas.

Material combines outstanding properties
The reason for the special properties of the substrate lies in its structure. "This is where different materials with outstanding properties come together," says Dr. Salih Veziroglu, who is researching the substrate materials as part of a grant from the CAU research focus KiNSIS ( Kiel Nano, Surface and Interface Science ). "For example, it consists of an extremely active photocatalytic titanium dioxide layer and special plasmonic nanostructures." The researchers combined four different nanostructures on the surface of the substrate, including gold and silver particles, between which there are light-matter interactions - so-called plasmonic effects.

With their substrate, the CAU team has made a contribution to a new approach to Raman spectroscopy, the recently presented PIERS method (Photo Induced Enhanced Raman Spectroscopy). The combination of plasmonic and photocatalytic effects significantly improves the Raman signal and thus the resolution of the method.

Addition of AI methods and spin-off planned
"This substrate is the result of many years of research and various expertises at our chair. Now we want to put our findings from basic research into practice,” says director Prof. Franz Faupel. The substrate can be integrated into other Raman spectroscopy methods and thus makes various possible applications conceivable. In order to bring it to market, the researchers are now looking for other research groups and companies in laboratory and analysis technology. They also plan to supplement their approach with artificial intelligence methods in order to create a comprehensive data basis for material analysis. In this way, individual molecules should also be able to be determined even faster and more precisely.

Doctoral student Shondo has already researched an idea for a specific application in his doctorate, which is about to be completed. In 2018, the materials scientist came to Kiel University with a scholarship from the German Academic Exchange Service (DAAD) to do something about environmental pollution in his home country Nigeria. The extraction of the country's vast oil reserves pollutes soil, rivers and even drinking water. With the new substrate that he and his colleagues in Kiel have developed, he also sees potential for using portable Raman spectroscopy devices in Nigeria: "Since it can be used to detect and even remove small amounts of oil, this method could already be used be used early and prevent worse environmental damage.”

About The CAU Research Focus KiNSIS
In the nanocosm other quantum physical laws prevail than in the macroscopic world. Understanding structures and processes in these dimensions and implementing the findings in an application-oriented manner is the goal of the research focus "Nanosciences and Surface Research" (Kiel Nano, Surface and Interface Science - KiNSIS) at the Christian-Albrechts-Universität zu Kiel (CAU). In an intensive interdisciplinary cooperation between physics, chemistry, engineering and life sciences, this could result in novel sensors and materials, quantum computers, advanced medical therapies and much more. For more information, visit www.kinsis.uni-kiel.de.