Whether contaminated drinking water or harmful gases – many pollutants enter the environment unnoticed and are difficult to detect. Their identification often requires specialized laboratories, expensive measuring devices, and long analysis times. In many regions of the world, regular environmental monitoring therefore remains difficult. Tomáš Lednický is working on an alternative: optical sensors based on gold nanoparticles, designed to measure water and air quality more precisely, quickly, and at lower cost.

A sensor that detects pollutants with light – compact, cost-effective, and, with portable measuring systems, potentially usable even outside specialized laboratories: In his postdoctoral project at Leibniz IPHT, Dr. Tomáš Lednický is researching how gold nanoparticles can be fabricated as optical sensors and optimized for different applications.

Tomáš Lednický studied Physical Engineering and Nanotechnology in Brno, Czech Republic, and completed research stays in France and Austria. With a Marie Skłodowska-Curie Fellowship (MSCA) from the EU, he came to Leibniz IPHT in Jena for his postdoctoral project DESIRE. “The institute gives me the opportunity to collaborate with international partners and to advance my research on LSPR sensors,” says Tomáš Lednický. Particularly important, he emphasizes, is an interdisciplinary approach that connects nanofabrication and biosensing.

Gold as a precision tool

Gold is more than a precious metal – at the nanoscale it becomes a powerful sensor. Gold nanoparticles interact with light, and their optical properties change depending on their immediate surroundings – an effect known as localized surface plasmon resonance (LSPR). “The idea is simple: the sensors work like optical litmus paper,” explains Tomáš Lednický. “When a molecule binds to the gold surface, the transmitted light changes – and we can measure that.”

However, the sensor does not react specifically to individual substances, but to any change in its environment – such as the refractive index. “Our sensors are very sensitive, but not inherently selective,” says Tomáš Lednický. “To detect specific compounds, we need to functionalize them.” This is done by coupling suitable molecules to the gold nanoparticles: for example, DNA sequences that bind only to complementary genetic information – such as that of viruses or bacteria. “Likewise, we can use molecules that detect hormones, pharmaceutical residues, or heavy metals. This functionalization makes our sensors extremely versatile.”

Highly sensitive sensors – without high costs

Fabricating ordered nanostructures smaller than 100 nanometers over large areas is complex and expensive. Electron beam lithography, a technique for precise nanostructuring, can drive production costs up to ten thousand euros per wafer. Tomáš Lednický has developed an alternative method that drastically reduces these costs.

This involves creating a self-organized, honeycomb-like oxide layer on aluminum, which is then removed. This results in a fine network of nanoscale indentations that serves as a template for a gold layer. When heated, nanoparticles form through dewetting. “Even at relatively low temperatures, tiny gold droplets form – similar to water droplets when a thin layer of ice melts,” says Tomáš Lednický. The result: highly sensitive sensors that can be produced for less than five euros per square centimeter.

More precise evaluation of sensitivity

An important step in sensor development is evaluating their sensitivity. Plasmonic sensors are often calibrated using liquids with different refractive indices. However, at the nanoscale, this method can lead to inaccuracies – for example, due to the formation of thin adsorption layers.

To address this, in 2024 Tomáš Lednický and other researchers developed a new approach for objectively assessing plasmonic sensors – demonstrated on gas sensors. “Until now, there was no standardized way to compare the performance of such sensors,” he explains. Their model takes into account the sensitivity decay from the nanoparticle surface as well as the thickness of the measured layer. “This allows us, for the first time, to quantify which sensors are truly more sensitive – regardless of the detection medium.”

Gas detection is a particularly demanding test field. “Gases are difficult to detect, mainly because of their stability and low refractive index,” says Tomáš Lednický. To tackle this challenge, he is working on coating gold nanoparticles with ultrathin layers of known gas-reactive materials such as tungsten oxide or zinc oxide. This enables the sensors to respond specifically to certain gases. A decisive advantage over many commercial gas sensors: they operate at room temperature, enable remote detection – and at significantly lower costs.

International collaboration for global solutions

Tomáš Lednický collaborates with researchers worldwide, including from Hungary, Portugal, and the Czech Republic. Recently, he presented his research results at the IEEE-Nano Conference in Spain and at the Eurosensors Conference in Hungary. “Many laboratory techniques that are standard in Europe are not available elsewhere,” says Tomáš Lednický. “If we can develop a technology that is precise, affordable, and easy to use, we could make environmental and health analysis more accessible to many people.”

Publication: Proença, M., Lednický, T., Meira, D. I., Rod- rigues, M. S., Vaz, F., Borges, J., & Bonyár, A. (2024). New parameter for benchmarking plasmonic gas sensors demonstrated with densely packed Au nanoparticle layers. ACS Applied Materials & Interfaces, 16(42), 57832–57842. https://doi.org/10.1021/acsami.4c11102