CAMBRIDGE — The garden is marvelously lush, with hundreds of blossoming roses, tulips, lilies, and curvaceous, fungi-like plants. But these petals, twisting stems, and finely wrought leaves are invisible to the naked eye: Grown in the lab, this nano-landscape of crystals is best seen with an electron microscope.
The creation of Harvard researchers, the “garden’’ is a demonstration of how simple environmental changes, such as tweaking the temperature, can be used to precisely control the construction of tiny objects and devices — at a scale that is a fraction of a fraction of the width of a human hair.
Scientists toiling in this microscopic realm are putting their new techniques to aesthetically pleasing purposes to show they work, and to capture the public’s imagination.
The ultimate goal is to come up with industrial applications. Researchers envision a new generation of tiny medical sensors and microelectronics, not to mention materials possessing novel properties that could, for example, allow those materials to interact with light to enable as-yet-to-be-invented technologies.
“In nature, you see many complex shapes and patterns,” said Wim Noorduin, a postdoctoral researcher at Harvard University who grew the flowers featured Thursday in the journal Science. “There’s a huge interest to grow complex shapes at the microscale,” by harnessing nature’s ability to create detailed and intricate structures, such as those found in a coral reef or on a seashell.
On the ground floor of the Cambridge building where Noorduin works, researchers, wearing masks and protective suits to guard against dust and other contaminants, use sophisticated techniques to build nanoscale structures. Noorduin is working at a similar scale, but his work can be done in a simple glass beaker — he’s even done it in a coffee cup — using readily available ingredients found in most laboratories.
The technique is remarkably easy: fill a beaker with a solution that has a salt and a silicon compound dissolved in it. Put in a glass slide or a bit of metal to act as the soil on which the crystal “plants” will grow. Allow carbon dioxide from the air to diffuse into the solution, triggering a simple reaction that causes the dissolved chemicals to come out of the solution and form a solid crystal — one that is curvy, rather than jagged.
Noorduin often used whatever was at hand for his experiments, in one case growing a surreal, densely packed garden around the base of the Lincoln memorial on a shiny penny.
He got his first glimpse of what he had grown three years ago: a black-and-white electron microscope image that has the crowded, slightly alien look of a fully imagined Pixar world. Stems balloon into horn shapes, stalks curve upward. It took his breath away. Then, he buckled down to figure out how he had created the breathtaking image and how he could modify it. He later added dyes to the solution he was growing at different stages, but the electron microscope images have to be artificially colored.
Noorduin took his cues from nature: As a shell is forming, its pattern can change in response to differences in the environment. By changing the acidity of the solution and the temperature, he discovered controlled ways to make his garden grow. He even accidentally discovered, when he put a cover on a beaker to keep out dust, that controlling the concentration of carbon dioxide could alter the thickness of his petals.
Working with materials science professor Joanna Aizenberg, Noorduin discovered that altering the acidity or alkalinity of a solution could cause crystal blossoms to grow outward into a bell shape, or make them curl inward. Combining various techniques, they could create tendrils, the nested layers of petals in a rose, and the delicate cup of a tulip — which Noorduin felt especially obligated to grow, because he is Dutch.
Juan Manuel Garcia-Ruiz, a research professor at CSIC-University of Granada in Spain, demonstrated a decade ago that crystals could grow in unexpected curves and spirals. For years, he said, no one believed that the crystal forms he grew, which so closely resembled living forms, were really crystals — assuming instead there was just biological contamination.
He said the new research brings a finer level of control to the process, showing how it is possible to modify the shapes.
It also falls into a growing field of fabricating microstructures, ranging from making whimsical smiley faces by folding strands of DNA, to Lego-like structures that spell out the alphabet made of DNA “bricks.”
Scientists not involved in the work appreciated its beauty. But they said that deciding to make tiny pieces of art isn’t mere whimsy.
Hendrik Dietz of the Laboratory for Biomolecular Nanotechnology at Technische Universität München in Germany, wrote in an e-mail that the ability to build something beautiful is only possible once it’s possible to control matter at the small scale. Thus, the intricate sculpture-like flowers are a way to judge the scientists’ level of control.
“Beautiful (or funny) things such as DNA smiley faces, etc., should therefore not be taken easily as child’s play,” Dietz wrote. “There is serious science . . . that has enabled the authors to pull these things off.”
Shawn Douglas, an assistant professor at the University of California, San Francisco, said that an unexpected shape that clearly bears the imprint of human imagination — such as a smiley face that would never appear in nature — is a way of showing that the technique is not an artifact. Instead, it shows scientists actually have control to build whatever they want.
“If you have to choose something to make, it almost seems obvious to choose a fun or interesting shape,” he wrote in an e-mail.