Coffee-stain effect: Indian scientists detect toxins at trillionth levels

A Bengaluru-based team has discovered a coffee-inspired, affordable way to detect banned dyes and contaminants in food at trillionth levels, offering a breakthrough in low-cost food safety testing

 

Indian scientists have made a new breakthrough in food safety using the “coffee-stain effect” to detect toxic dyes and contaminants in food products at trillionth levels, the Ministry of Science and Technology said in a statement.

 

In a study by the Raman Research Institute (RRI), Bengaluru, supported by the Department of Science and Technology (DST), Government of India, researchers found that the same everyday phenomenon that leaves a dark ring around a coffee cup could be turned into a powerful, low-cost method to spot deadly contaminants in food and water.

 

What’s the link between coffee cups and food safety?

 

When a coffee drop dries on the table, it forms a dark ring around the edge. This everyday pattern, called the coffee-stain effect, happens because particles in the liquid drift outward as it evaporates, clustering along the rim.

 

 

According to the ministry, the scientists realised that the same physics applies to other liquids too. By recreating the “coffee-ring” with nanoparticles, they found that these rings could become tiny optical landscapes, where light and matter interact in powerful ways. That is how they can spot toxins invisible to the naked eye.

 

How will this discovery help food safety efforts?

 

Some dyes are very harmful, such as Rhodamine B, a bright, fluorescent chemical used in textiles and cosmetics. It is banned in food because it can cause skin, eye, and respiratory damage. However, due to its low cost and eye-catching colour, it sometimes sneaks into food products or contaminates water sources. Regulators struggle to catch these tiny traces, especially when they are diluted to parts per trillion.

 

The RRI team mixed gold nanorods — microscopic golden sticks — with water and let the droplets evaporate on a silicon surface. As the water dried, the nanorods formed perfect ring-like patterns, just like coffee stains.

 

At the edges of these rings, the rods packed tightly together, creating hotspots — tiny areas where light is super-concentrated. When a laser hit those hotspots, even the faintest traces of Rhodamine B bound to the gold rods lit up dramatically under Surface-Enhanced Raman Spectroscopy (SERS).  ALSO READ| New light-based therapy kills cancer without harming healthy cells 

How powerful is this new technique?

 

According to the statement, with a small tweak, such as increasing how many nanorods were used, the system’s sensitivity improved by nearly a million times.

 

“This is a simple and cost-effective way to detect harmful substances,” explains Professor Ranjini Bandyopadhyay, Soft Condensed Matter group, RRI. “Even handheld Raman spectrometers could be used for toxin detection with this method,” she adds.

 

Could this change how we test food and water safety?

 

Right now, detecting illegal dyes or contaminants requires bulky lab equipment and costly procedures. This new method could change that, transforming something as common as the coffee-stain effect into a low-cost, portable, and ultra-sensitive test.

 

“The technique can be used for a wide range of harmful substances and can be transformed into advanced technology for reducing disease and environmental harm,” the statement said.