Researchers at Kaunas University of Technology (KTU) in Lithuania have developed highly sensitive, metal-free oxygen sensors with the potential to revolutionize multiple industries, including food packaging, medicine, and biotechnology. These organic compounds represent a safer, more sustainable alternative to traditional oxygen detection systems that rely on expensive and toxic heavy metals.

Led by Dr. Matas Gužauskas, the KTU team synthesized new materials whose luminescence changes visibly in response to oxygen levels. This enables real-time oxygen monitoring without the need for specialized equipment. In low-oxygen environments, the compounds glow more intensely and shift in color from blue to green—a change easily detectable with the naked eye.

“We developed two new materials that act as highly sensitive oxygen sensors. Their luminescence depends on the presence of oxygen—without it, the light intensifies and changes colour,” said Dr. Gužauskas. “This allows oxygen detection in a visually straightforward and accessible way.”

These innovative materials are based on thianthrene derivatives, organic molecules characterized by two sulfur atoms and a non-planar, bent structure. This unique design facilitates room-temperature phosphorescence (RTP), a property that is rare among organic compounds and especially valuable for oxygen sensing.

Phosphorescence involves long-lived light emission, making it particularly susceptible to interference from oxygen molecules. When oxygen interacts with these excited molecules, it quenches the emission—this fundamental principle forms the basis for oxygen detection in these sensors.

Traditionally, achieving RTP in sensors has required the use of expensive and toxic heavy metals like platinum or iridium. These materials pose challenges in fields such as medicine and food safety, where biocompatibility and environmental impact are critical concerns. By eliminating heavy metals, KTU’s innovation offers a non-toxic, scalable, and cost-effective solution.

One of the new compounds achieved a Stern–Volmer constant among the highest ever recorded for metal-free sensors, confirming its record-breaking sensitivity. This allows for rapid and accurate detection of even trace amounts of oxygen, making it ideal for sensitive applications.

Key potential applications include:

• Food packaging: Detecting seal breaches or spoilage by monitoring oxygen ingress.
• Cancer diagnostics: Identifying tumour hypoxia, a condition where oxygen deprivation is linked to disease progression.
• Biotechnology: Monitoring cell cultivation and metabolic processes.
• Environmental monitoring: Measuring oxygen in water or air.
• Smart packaging and security inks: Offering tamper-proof visual indicators for authentication or freshness.

According to Dr. Gužauskas, the synthesis process for these compounds uses well-established chemical reactions, allowing for easy scalability and commercial adaptation. The team is currently seeking partners to evaluate biological compatibility and explore further medical applications.

This research, part of the Technological and Physical Sciences Excellence Centre (TiFEC) initiative, was conducted alongside Dr. Rasa Keruckienė and PhD student Lukas Dvilys. Their work may not open an entirely new field, but it sets a new benchmark in oxygen sensing and positions KTU at the forefront of sustainable sensor technology.

For those interested in a deeper dive into the chemistry, the full article, titled “Thianthrene-based heavy metal-free oxygen analytes exhibiting room temperature phosphorescence and high sensitivity for low oxygen concentration”, is available in scientific literature.