Reusable Nanostructured Substrate for Highly Sensitive Pollution Detection

Reusable Nanostructured Substrate for Highly Sensitive Pollution Detection

Surface-enhanced SERS, also known as Raman scattering (or spectroscopy), is an advanced analytical technique that broadens the scope of Raman applications to trace analysis, such as part-per-million-level pollutant detection in water or other liquids. The use of SERS in biochemistry, forensics, food safety, danger detection, and medical diagnostics has a great potential.

However, there is still a need for reasonably priced and dependable SERS substrates that would enable reproducible spectrum signals before the technology can be used at the industrial and clinical levels.

The SERS technique was advanced by material scientists from Kiel University who created a novel substrate with plasmonic and photocatalytic nanostructures. It improves sensitivity, geographical and temporal resolution, and produces analyses that are 50 times more potent than those produced by traditional SERS.

Researchers designed this new substrate to be reusable, which significantly reduces the cost. Their results have been published in the journal Small.

The substrate plays a crucial role

Raman spectroscopy named after physicist and Nobel Prize winner Chandrasekhara Venkata Raman is a method of determining the chemical composition of materials. As a result, it can also find dangerous compounds.

This substrate is the result of many years of long-standing experience and various expertise in our Chair. Now we want to transfer our findings from fundamental research into an application.

Professor Franz Faupel

A material sample is exposed to laser radiation for this reason. Conclusions regarding the characteristics of the material can be made based on the reflected Raman signal.

“The substrate plays the most critical role in the performance of this analytic technique, because of interactions with the laser light influence the Raman signal,” explains Josiah Ngenev Shondo. As a doctoral researcher at the Chair for Multicomponent Materials, he works to improve the detection and photocatalytic clean-up of pollutants in water.

The researchers have now achieved success in creating a unique substrate for SERS analysis that increased the Raman signal by a factor of 50 in contrast to conventional SERS by combining materials with various properties.

“That’s more than has ever been reported before for this method,” says Professor Oral Cenk Aktas. That enormously increases the sensitivity, spatial, and temporal resolution in analysis of materials at trace amounts.

As a result, even very small amounts of material can now be analyzed in a short time. The substrate is exposed to UV radiation for activation and cleanup before and after the material analysis, respectively.

“This way the analyte is decomposed and the substrate, which is quite costly, can be re-used several times now. We showed that our substrate can be reused at least twenty times without any loss of its Raman activity,” Aktas continues.

Substrate carries SERS approach to an advanced level

The researchers created the novel surface with a composition of nanocolumnar structures, a nanocrack network, nanoscale mixed oxide phases, and nanometallic structures (“4N-in-1”). This surface enhances the Raman signal and provides a high detection sensitivity. Recently PIERS (Photo Induced Enhanced Raman Spectroscopy), a new extension of SERS method, has been proposed.

The research team’s new “4N-in-1” PIERS substrate combines photocatalysis and plasmonic principles to produce excellent resolution and signal amplification in SERS analysis.

“Our substrate brings various superior properties together on the same substrate. In addition to the plasmonic nanostructures, it is composed of extremely active titanium dioxide layer,” says Dr. Salih Veziroglu.

Further plans: Spin-off and combination with AI methods

“This substrate is the result of many years of long-standing experience and various expertise in our Chair. Now we want to transfer our findings from fundamental research into an application,” says Professor Franz Faupel, head of the Chair. Their substrate can easily be combined with any type of Raman spectroscopy, and this may trigger various new applications.

They are searching for other research teams and businesses in laboratory and analytical technology to help them commercialize their cutting-edge Raman spectroscopy technique. In order to build a substantial data foundation for materials analysis, they also intend to incorporate their methodology with artificial intelligence (AI). This could enable faster and more precise detection of individual molecules.

In his soon-to-be-completed doctoral thesis, Shondo already looked into one proposal for a practical implementation. In 2018, the materials scientist came to Kiel University with a scholarship from the German Academic Exchange Service (DAAD) intent to do something about the environmental pollution in his home country of Nigeria. Large oil deposits in the nation are being extracted, which contaminates the soil, rivers, and even drinking water.

With the new substrate Shondo and his colleagues have developed, he sees potential for using it with portable Raman spectroscopy equipment in Nigeria: “Since even small amounts of oil can be detected and even removed, this method could be used at an early stage and prevent worse environmental damage.”