Detecting pathogens with nanosensors

Spectroscopic analysis methods can be used to detect pathogens such as bacteria or viruses - for example hospital germs, waterborne pathogens or zoonotic pathogens such as coronaviruses - with high sensitivity even in the smallest samples.

To this end, researchers are specifically producing nanostructures with desired optical properties in order to combine them with (bio)molecular components such as DNA and use them as optical markers and sensors.

To do this, they use localized surface plasmon resonance (LSPR), a special property of noble metal nanoparticles and nanostructures that is excited by electromagnetic radiation such as light. Another method to design structures for spectroscopic detection of pathogens is surface-enhanced Raman spectroscopy (SERS). Here, researchers use optical effects to significantly increase signal intensity in vibrational spectroscopy.

One sensor, two analysis methods

A research team from Leibniz IPHT, together with German and Japanese researchers, is now developing a nanosensor that combines both methods. As part of the PlasmonBioSense project, the research partners are developing and testing novel multifunctional sensor substrates for applications in localized surface plasmon resonance spectroscopy (LSPR) and surface-enhanced Raman spectroscopy (SERS). The research partners are from Osaka and Kure, and from Temicon Gmbh, Furuno Electric Co, and Tanaka Kinzoku Kogyo KK.

Nanostructured gold sensors serve as the basis for the substrates. These can be fabricated using a low-cost replication technique - nanoimprint lithography (NIL). Combined with nanoparticles, these enable extremely high local amplification of the electromagnetic field. This allows high sensitivity to be achieved for both analytical techniques - LSPR and SERS.

Detect pathogens in the smallest concentrations

"We combine our experience in developing bioanalytical methods based on nanosensors with the know-how of the German company partner, who comes from the field of structuring," explains Andrea Csáki. The scientist heads the nanobiophotonics working group at Leibniz IPHT and is organizing the PlasmonBioSense project together with project coordinator and research department head Wolfgang Fritzsche.

"We are developing novel and highly sensitive substrates with which it will be possible to analyze a sample with the two complementary methods LSPR and SERS," says Andrea Csáki. Because of the increased sensitivity in this way, the sensors should provide better results at lower concentrations than current SERS and LSPR sensors. The researchers' goal is to create a reproducible manufacturing process for the substrates.

Applications for the novel nanosensors could include DNA-based bioanalytics, particularly for the detection of pathogens. These include aquatic pathogens and hospital germs as well as zoonotic pathogens, including coronaviruses. "With this innovative setup, we hope to also facilitate the diagnosis of diseases in the future," says Wolfgang Fritzsche. For example, the sensors could serve as a basis for immunoassays to detect autoimmune diseases and immune stages.

Background Information: Localized Surface Plasmon Resonance

Nanoparticles made of gold or silver interact with light under certain conditions. The free electrons in the metal atoms of the particles then start to vibrate coherently, i.e. at the same frequency. The collective oscillations of the electrons parallel to the surface of the metal are called localized surface plasmons. They absorb and scatter visible light of different wavelengths depending on the size, shape and material of the nanoparticles and their environment.

The latter is made use of by researchers to find answers to bioan-alytical questions. If an analyte molecule binds to the recognition structures on the surface of the metal nanoparticles, the refractive index - and therefore the wavelength - of the surface plasmons on the metal surface there changes. The spectral change is recorded and evaluated.

Source: Leibniz Institute of Photonic Technology (IPHT)