New Delhi, Oct 13 (NationPress) Researchers at the Raman Research Institute (RRI), an autonomous body funded by the Department of Science and Technology (DST), have harnessed the unique phenomenon of coffee stains to identify harmful dyes in food products.

When a drop of coffee dries on a surface, it leaves behind a characteristic dark ring at the edges. This coffee-stain effect occurs because the particles suspended in the liquid migrate outward as it evaporates.

Utilizing this effect, the research team devised a technique to detect Rhodamine B, a fluorescent synthetic dye commonly found in textiles and cosmetics, within food items.

This dye is hazardous, posing risks to the skin, eyes, and respiratory health, and is a significant environmental pollutant that can remain in water sources.

“Dye substances like Rhodamine B are prohibited in food and cosmetic products due to their toxicity, yet regulators struggle to monitor their unauthorized usage, especially in minimal quantities and due to a lack of adequate detection tools,” explained A. W. Zaibudeen, a researcher at RRI.

“Once these dyes contaminate food or water, they can dilute to concentrations as low as parts per trillion, complicating detection with standard techniques. Thus, a more sensitive detection approach, such as Surface-Enhanced Raman Spectroscopy (SERS), is essential,” added Yatheendran K. M, Engineer B in Soft Condensed Matter.

The team utilized the coffee-stain effect with gold nanorods, which are microscopic rods measuring a few tens of nanometers, by applying a water droplet containing them on a thoroughly cleaned silicon surface that strongly attracts water. As the water evaporates, the rods gather at the edge, forming a ring. When a laser targets the stain, Rhodamine B molecules attached to the gold rods in these regions emit significantly brighter optical signals than they would independently.

At lower concentrations of gold nanorods, only relatively high amounts of Rhodamine B could be recognized — comparable to a drop of dye in a glass of water. However, as the concentration of nanorods increased, the detection limit improved dramatically.

With the densest ring deposits, the system could identify Rhodamine B at a concentration as low as one part in a trillion. Notably, a hundred-fold increase in nanorod concentration resulted in an almost million-fold enhancement in sensitivity.

The researchers demonstrated that it is feasible to utilize a simple, naturally occurring pattern created by the same phenomenon that produces coffee rings on tables, transforming it into an exceptionally powerful and cost-effective method for chemical detection.

This technique has the potential to be adapted for detecting a broad array of harmful substances, paving the way for advanced technologies aimed at mitigating disease and environmental damage, according to the research team.