Bubble-pen lithography — which relies on microbubbles to inscribe, or write, nanoparticles onto a surface — has been demonstrated to efficiently handle nanoparticles used in micro- and nanomanufacturing. The ability to handle the tiny particles of gold, silicon and other materials could ease fabrication of biomedical sensors, optical computers, solar panels and other devices. Some nanoparticles have optical properties that are useful for electronics, while others have the ability to absorb solar energy. In biomedical applications, nanoparticles can serve as drug carriers or imaging agents. Despite their potential, nanoparticles’ small size make them difficult to handle, and manipulation can affect their properties and functions. Furthermore, existing lithography methods, which are used to etch or pattern materials on a substrate, are not capable of fixing nanoparticles to a specific location with precise and arbitrary control. "The ability to control a single nanoparticle and fix it to a substrate without damaging it could open up great opportunities for the creation of new materials and devices," said University of Texas at Austin professor Yuebing Zheng. "The capability of arranging the particles will help to advance a class of new materials, known as metamaterials, with properties and functions that do not exist in current natural materials." Zheng and his team at UT Austin developed and patented the device and technique, which they said could also helpful for science and medicine because researchers would be able to precisely control cells, biological material, bacteria or viruses for study and testing. Using the bubble-pen device, the researchers focused a laser underneath a sheet of gold nanoscale islands to generate a hotspot that created a microbubble out of vaporized water. The bubble attracted and captured a nanoparticle through a combination of gas pressure, thermal and surface tension, surface adhesion and convection. The laser then steered the microbubble to move the nanoparticle on a site on the surface. When the laser was turned off, the microbubble disappeared, leaving the particle on the surface. If necessary, the researchers can expand or reduce the size of the microbubble by increasing or decreasing the laser beam's power. The team demonstrated that bubble-pen lithography can leverage a design software program in the same way as a 3D printer, deposited nanoparticles in real time in a preprogrammed pattern or design. The researchers were able to write the UT Austin Longhorn symbol and create a dome shape out of nanoparticle beads, as demonstrated in the video below. A major advantage of the technique is the high speed at which it can test prototypes and ideas for devices and materials, the researchers said. It also has the potential for large-scale, low-cost manufacturing of nanomaterials and devices, as existing lithography techniques require more resources and a clean room environment. The team seeks to advance bubble-pen lithography by developing a multiple-beam processing technique for industrial-level production of nanomaterials and -devices. Zheng is also planning to develop a portable version of the technique that works like a mobile phone for use in prototyping and disease diagnosis. The research received funding from the Beckman Young Investigator Award and was published in Nano Letters (doi: 10.1021/acs.nanolett.5b04524).