Daijiworld Media Network - New Delhi
New Delhi, Oct 13: In a novel scientific breakthrough, researchers at the Raman Research Institute (RRI), an autonomous institute under the Department of Science and Technology (DST), have harnessed the everyday phenomenon behind coffee stains to detect one of the most harmful dyes illegally used in food — Rhodamine B — with remarkable sensitivity.
The discovery builds on a simple observation: when a drop of coffee dries on a surface, it leaves behind a dark ring at the edges, a result of suspended particles migrating outward as the liquid evaporates — a process widely known as the “coffee-stain effect.” Scientists at RRI turned this seemingly mundane occurrence into a powerful tool for chemical detection.
The research team applied this effect using gold nanorods — tiny particles just tens of nanometers in length. By placing a droplet containing these nanorods onto a clean, water-attracting silicon surface and allowing it to evaporate, they created a dense ring-like deposit where the rods clustered at the rim. When a laser was directed onto this ring, any Rhodamine B molecules that had adhered to the nanorods produced dramatically amplified optical signals, thanks to the nanostructures' unique ability to enhance molecular signatures through Surface-Enhanced Raman Spectroscopy (SERS).
Rhodamine B, a fluorescent synthetic dye banned in food and cosmetics due to its toxicity, has been notoriously difficult to detect in trace amounts. Used illegally for its bright coloring, the dye is known to cause harm to the skin, eyes, and respiratory system, and poses a significant threat as an environmental pollutant. Detecting it at extremely low concentrations — especially when diluted in food or water — has long been a challenge due to the limitations of conventional detection equipment.
The new technique proved to be extraordinarily sensitive. At low concentrations of gold nanorods, the system could detect Rhodamine B at levels comparable to a single drop in a glass of water. However, by increasing the concentration of nanorods, the detection limit improved exponentially — with the most concentrated ring patterns allowing detection down to just one part per trillion. This represents a near million-fold increase in sensitivity, achieved through a hundred-fold increase in nanorod concentration.
Lead researcher A. W. Zaibudeen noted the regulatory hurdles in monitoring banned dyes like Rhodamine B, particularly due to their illegal use in small quantities and the lack of accessible detection tools. Yatheendran K. M, an engineer involved in the study, emphasized the importance of SERS as a method capable of identifying these dyes even when they are present in incredibly diluted forms.
The RRI team’s innovation not only offers a low-cost and highly effective solution for detecting Rhodamine B but also opens the door to developing similar methods for identifying a wide range of harmful chemicals. By converting a common, natural phenomenon into a scientific detection method, the researchers have provided a new tool for public health and environmental protection — one that could transform how toxic substances are monitored and controlled in daily life.