A technique for producing nanoparticles that relies on microfluidics — the manipulation of tiny fluid droplets in narrow channels — shows promise for transforming expensive, batch-by-batch nanoparticle production into large-scale automated assembly. Nanoparticles are found in technologies ranging from drug delivery to automobile pollution controls to HD TV sets. With their tiny size and subsequently increased surface area, they're critical to industry and scientific research. Nanoparticles form in a 3D-printed microfluidic channel. Each droplet shown here is about 250 μm in diameter and contains billions of platinum nanoparticles. Courtesy of Richard Brutchey and Noah Malmstadt/USC. Gold nanoparticles, for example, have been shown to easily penetrate cell membranes without causing any damage, an unusual feat, given that most such penetrations can damage or kill the cell, said researchers from the University of Southern California. Their ability to slip through cell membranes makes gold nanoparticles ideal devices to deliver medications to healthy cells, or doses of radiation that will be fatal to cancer cells. With a single milligram of gold nanoparticles currently costing about $80, depending on size, that makes the price of gold nanoparticles at $80,000 per gram; a gram of pure, raw gold is worth about $50. "It's not the gold that's making it expensive," said professor Noah Malmstadt of the USC Viterbi School of Engineering. "We can make them, but it's not like we can cheaply make a 50-gallon drum full of them.” “In order to go large scale, we have to go small,” said chemistry professor Richard Brutchey of the USC Dornsife College of Letters, Arts and Sciences, so the team turned to microfluidics. The researchers 3D-printed tubes about 250 μm in diameter — which they believe to be the smallest, fully enclosed 3D-printed tubes anywhere. A 3D-printed microfluidic chamber mass-produces platinum nanoparticles. Courtesy of Richard Brutchey and Noah Malmstadt/USC. They then built a parallel network of four of these tubes, side-by-side, and ran a combination of two nonmixing fluids (like oil and water) through them. As the two fluids fought to get out through the openings, they squeezed off tiny droplets. Each of these droplets acted as a microscale chemical reactor in which materials were mixed and platinum nanoparticles were generated. Each microfluidic tube could create millions of identical droplets that perform the same reaction, the researchers said. Systems like this have been envisioned in the past, but scale-up has not been possible because the parallel structure meant that if one tube got jammed, it would cause a ripple effect of changing pressures along its neighbors, knocking out the entire system. Brutchey and Malmstadt bypassed this problem by altering the geometry of the tubes themselves, shaping the junction between the tubes such that the particles come out a uniform size and the system is immune to pressure changes. The research was published in Nature Communications (doi: 10.1038/ncomms10780).