Melanocytes

Eyes aren’t the only human organ that can “see” light. It turns out that skin cells called melanocytes have a light-receptor molecule called rhodopsin that fluoresces as soon as it detects ultra-violet A light (UVA), the deeper penetrating, long-wavelength UV light, as shown here.

Until now, researchers have only found rhodopsin in the eye, where it helps the eye adapt to low-intensity light and is an integral first responder to the perception of any light. When light strikes rhodospin in the retina, rhodopsin reacts by chemically breaking down, which triggers a nerve signal.

In melanocytes, rhodopsin has a different, but extraordinary role. The rhodopsin causes the cells to fluoresce in response to UVA light while triggering an early, important step in melanin production: a spike in calcium signaling. Melanin — the skin pigment that absorbs radiation and produces a tan — protects DNA in skin cells from UV damage.

Previously, scientists thought melanin production began long after radiation damaged the skin. Now it seems that the process of producing melanin begins as soon as the skin “sees” radiation through its light-recepting molecule!

Photo: Elena Oancea/Brown University

Conjoined spheres take the shape of a long four-wheeled vehicle,
which drives on a surface of yellow balls.

Buckle your tiny seatbelts. Scientists have created a car at the nano scale.

Just how small is nano? One nanometer equals one billionth of a meter. To help you wrap your head around that, the average sheet of paper is about 100,000 nanometers thick. Measuring in at 4 nanometers by two nanometers, this car is about one billion times smaller than a Volkswagen Golf.

Made from a single molecule, electricity powers the movement of the nano car’s wheels, which can be driven in a straight line and in a controlled manner.

What’s more, the nano car emits neither greenhouse gases nor any noise, a talent it does not share with its bigger cousins.

But like any vehicle, it has its flaws. For example, it has terrible “gas mileage.” Scientists need to refuel it after every half revolution of its wheels. To do so, they give the wheels an electric zap through the sharp, wire tip of a scanning tunneling microscope, an imaging instrument. Also, the nano car can’t drive in reverse.

The nano car is the first foray into designing molecular transport machines, a fancy phrase for microscopic vehicles, which could help scientists carry out tasks at the nano scale.

Photo: Empa

Scattering affects the color of light coming from the sky, but the details are determined by the wavelength of the light and the size of the particle. The short-wavelength blue and violet are scattered by molecules in the air much more than other colors of the spectrum. This is why blue and violet light reaches our eyes from all directions on a clear day. But because we can’t see violet very well, the sky appears blue.

Scattering also explains the colors of the sunrise and sunset, Ackerman says.

“Because the sun is low on the horizon, sunlight passes through more air at sunset and sunrise than during the day, when the sun is higher in the sky. More atmosphere means more molecules to scatter the violet and blue light away from your eyes. If the path is long enough, all of the blue and violet light scatters out of your line of sight. The other colors continue on their way to your eyes. This is why sunsets are often yellow, orange, and red.”

And because red has the longest wavelength of any visible light, the sun is red when it’s on the horizon, where its extremely long path through the atmosphere blocks all other colors.