How a Common Food Dye in Products Like Mountain Dew & Skittles Can Turn Mice Transparent

Do you know how scientists can see inside live animals without the need for invasive procedures? It turns out that a common food dye (also used in Doritos!) can help make this possible. 

By using this dye, researchers can make mice partially transparent, allowing them to see inside the animals without cutting them open.¹ This method makes it easier to study and understand the internal organs and tissues of live animals in detail.

Making Mouse Tissues Transparent with Food Color

The study found that a common food dye, known as tartrazine (Yellow 5), approved by the US Food and Drug Administration, (ref) can make the skin, muscles, and connective tissues of live rodents transparent. 

Researchers tested this by using tartrazine in both artificial tissues and real biological samples. They confirmed that the dye works by making tissues clear, which allowed for very detailed imaging.

By making the belly of a live mouse transparent, researchers could see and track fluorescently labeled neurons in the gut, observing how they move with the gut’s natural motions.

This helped create detailed maps of gut movement patterns over time. The method was also used to visualize blood vessels in the mouse’s scalp and to examine muscle details in the hindlimb with high resolution.

How Tartrazine Dye Makes Mouse Tissues Clear

Tartrazine dye, by absorbing blue light very effectively, changes how water bends light to be more like fat, according to the researchers. This happens because of a basic physical principle called the Kramers-Kronig relations.(ref) 

This principle explains that light waves behave in predictable ways. As a result, the dye makes light pass through skin more smoothly, as if the tissue were uniform. This helps light travel straight through, making it easier to see inside a mouse.

How Absorbing Molecules Can Make Live Animals Transparent

In the study, the researchers have found something surprising: molecules that strongly absorb light can actually make live animals transparent. 

According to the Lorentz oscillator model, molecules with certain properties—like long wavelengths, sharp absorption peaks, and lots of free electrons—can make the surrounding medium more transparent than traditional methods. 

There are still some challenges, such as making sure the different tissues match in transparency and how well the absorbing molecules can spread through the tissues.

Testing Tartrazine for Better Transparency

The researchers focused on tartrazine and a few other pigments to see if they could make tissues more transparent.

They tested these dyes in different materials like liquid with silica particles, raw chicken breast, live mice, and other mouse tissues to check how well the dye spread and how deep it penetrated. 

They also combined the dye with advanced microscopy techniques to see if it could enhance current technology.

To ensure safety, they did an initial toxicity test, checking both short-term and long-term effects in mice and tracking how quickly the dye was removed from their bodies through urine and feces. 

They found that tartrazine passes through the body within 24 hours, causes minimal inflammation or irritation, and has very low overall toxicity.

Limitations of the Transparency Method

While this method shows promise, it’s not perfect. It can’t make an entire living mouse invisible or let us see inside an entire human abdomen. 

For example, tartrazine only penetrates so far into tissue, so it’s not useful for imaging through thicker tissues without a targeted approach and a good understanding of the right concentration. 

Although the dye reduces light scattering, it doesn’t eliminate it completely, so thicker tissues will still result in darker, less clear images. (ref) While initial tests suggest it is relatively safe, further long-term studies are needed to confirm its complete safety.

Source:

1. Science