Lab-Created Lithoparticles Could Have Many Uses

Billions of fluorescent microscale particles in the shapes of all 26 letters of the alphabet have been designed and produced in the lab. The letters are made of solid polymeric materials dispersed in a liquid solution, and the scientists who created them anticipate that their "lithoparticles" will have significant technological, medical and scientific uses.

UCLA professor Thomas G. Mason and chemistry graduate student Carlos J. Hernandez mass-produced microscale particles shaped like each letter of the alphabet. Graduate student James Wilking used "laser tweezers" to pick up the letters 'U, C, L, A' and move them in order "like skywriting in solution." (Image: James N. Wilking/Thomas G. Mason, UCLA Chemistry)

"We have demonstrated the power of a new method, at the microscale, to create objects of precisely designed shapes that are highly uniform in size," said Thomas G. Mason, UCLA associate professor of chemistry and a member of the university's California NanoSystems Institute. "They are too small to see with the unaided eye, but with an optical microscope, you can see them clearly; the letters stand out in high fidelity. Our approach also works into the nanoscale."

Chemistry graduate student Carlos J. Hernandez designed a customized font for the letters and produced them. "We can even choose the font style; if we wanted Times New Roman, we could produce that," Mason said.

Hernandez and Mason have also produced particles with different geometric shapes, such as triangles, crosses and doughnuts, as well as 3-D "Janus particles," which have two differently shaped faces. The research is scheduled to be featured on the cover of the March 29 issue of the Journal of Physical Chemistry C; Mason is study co-author and Hernandez is lead author.

"We have made fluorescent lithographic particles, we have made complex three-dimensional shapes and, as shown by UCLA postdoctoral fellow Kun Zhao, we can assemble these particles, for example, in a lock-and-key relationship," said Mason, whose research combines aspects of chemistry, physics, engineering and biology. "We can mass-produce complex parts having different controlled shapes at a scale much smaller than scientists have been able to produce previously. We have a high degree of control over the parts that we make and are on the verge of making functional devices in solution. We may later be able to configure the parts into more complex and useful assemblies.

"How can we control and direct the assembly of tiny components to make a machine that works? Can we cause the components to fit together in a controlled way that may be useful to us? Can we create useful complex structures out of fundamental parts, in solution, where we can mass-produce a small-scale engine, for example? We will pursue these research questions," Mason said.

In the early 1990s, Mason founded a field called "thermal microrheology," the techniques of which are now used by scientists worldwide. Microrheology is a method for examining the viscosity and elasticity of soft materials, including liquids, polymers and emulsions, on a microscopic scale. Mason and Hernandez's research in the Journal of Physical Chemistry C provides novel probes for microrheology.

A "colloidal alphabet soup" created by billions of alphabet-shaped fluorescent microscale particles designed and mass-produced by UCLA's Mason and Hernandez. (Image: Carlos J. Hernandez/Thomas G. Mason, UCLA Chemistry)

Because each letter is smaller than many kinds of cells, possible applications include marking individual cells with particular letters. It may be possible, Mason said, to use a molecule to attach a letter to a cell's surface or perhaps even insert a letter inside a cell and use the letter-marker to identify the cell. The research also could lead to the creation of tiny pumps, motors or containers that could have medical, as well as security, applications.

In addition to creating the letters, Mason's research group can pick them up and reposition and reorient them in a microscale version of the game Scrabble.

"We have used 'laser tweezers' to pick up the jumbled letters 'U, C, L, A' and move them together in order, like skywriting in solution," Mason said. UCLA chemistry graduate student James Wilking moved the letters to spell "UCLA."

Mason's research is funded in part by the National Science Foundation. He also receives support from UCLA's John McTague Career Development Chair, which provides research funding for five years. UCLA has applied for a patent on the technology.

For more information, visit: www.ucla.edu