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Marb's Lab Builds an Arduino-Compatible Molecular Switch, Flipped with Laser Beams

Demonstrating the concept of photochromism, this clever switch uses a pair of laser beams to very visibly "switch" a spiropyran sample.

Gareth Halfacree
1 month agoHW101

Pseudonymous YouTuber "Marb," of Marb's Lab, has designed a photochromic molecular switch — controlled by an Arduino Micro-compatible development board and a custom PCB.

"Photochromic compounds are the necessary building blocks for light-driven molecular motors and machines," Marb explains by way of introduction to the project. "Upon irradiation with light, photoisomerization about double bonds in the molecule can lead to changes in the cis- or trans-configuration. These photochromic molecules are being considered for a range of applications."

This Arduino-compatible molecular switch flips based on the input of two laser beams passing through a beam splitter. (📹: Marb's Lab)

Defined as a molecule which can flip between at least two stable sates, and whose states can be read by spectroscopy, a photochromic molecular switch works at its base almost exactly like any other: it can be switched off, and it can be switched on. In this case, though, you're not flicking a toggle with your finger — you're slamming molecules with laser light.

To prove the concept, Marb designed a photochromic switch under the control of an Arduino Micro-compatible development board. A custom PCB houses 3D-printed mounts for two lasers, one at the 650nm wavelength and one at 405nm and both rated for 10mW sustained output power, their drivers, a voltage regulator, a temperature sensor, and a beam splitter.

"The beam splitter is not ideal," Marb admits of the cubic device, "as you lose 50 per cent [of the energy] when combining the laser beams. A dichroic mirror would be better, but it was not possible to find one at a reasonably low price."

The job of the beam splitter is to get both lasers pointing towards the target: a quartz cuvette housing two-part epoxy resin mixed with a pigment powder containing spiropyran, a photochromic compounds which can be flipped into a merocyanine form and back again — with, handily, a color change visible to the human eye, requiring no expensive expansive equipment to verify the switch's state change.

The full project video is embedded above and available on the Marb's Lab YouTube channel; a schematic for the circuit is included.

Gareth Halfacree
Freelance journalist, technical author, hacker, tinkerer, erstwhile sysadmin. For hire: freelance@halfacree.co.uk.
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