This post is part of our ongoing series of public-friendly summaries describing research articles that have been published by members of the Center for Sustainable Nanotechnology. Sam Lohse, the first author on this paper, was a post-doctoral student at the University of Illinois and is now an assistant professor at Colorado Mesa University in Grand Junction, CO.

He says, “Everyone (researchers, industry, etc.) wants nanomaterials, in order to test their fantastic applications and their implications for human health. Unfortunately, it can be difficult and frustrating even for experienced nanotechnology researchers to synthesize high-quality nanomaterials in meaningful quantities. We were hoping to come up with a simple and accessible approach to make nanomaterials in quantities of more than a gram at a time.”

The article was published in May 2013 in the journal ACS Nano.¹

“A Simple Millifluidic Benchtop Reactor System for the High-Throughput Synthesis and Functionalization of Gold Nanoparticles with Different Sizes and Shapes”

Even though researchers have been making a variety of nanoparticles for years, making NPs in large quantities is still a technical challenge. While we have the industrial capacity to make many chemicals (like polymers) on a scale of metric tons per year, it’s still very hard to make high-quality nanomaterials in quantities of more than a few milligrams per batch.² Many types of nanoparticles can only be made about 50 mg at a time, which means you would have to make nearly a trillion batches of nanoparticles to match the world-wide production levels of something like polystyrene, a common polymer molecule used to make plastic and foam. Unlike many traditional manufactured chemicals, it is very difficult to simply scale up the production of nanomaterials without losing control over the quality of the product. Our general inability to prepare nanoparticles on a large scale could act as a huge roadblock to commercializing nanoparticle-enabled technologies, and makes it very challenging to produce nanoparticles in sufficient quantities to study their biological effects or test their performance as therapeutics in clinical trials.

For the project we wrote about in this paper, our goal was to develop a simple approach to producing high-quality nanoparticles at the gram scale (a gram is a thousand milligrams). We wanted to develop an approach that could be potentially applicable to the synthesis of a number of different types of nanomaterials, and that would be accessible to many different would-be nanoparticle synthesizers, ranging from undergraduate chemistry students to small companies looking for an easy, scalable nanoparticle synthesis method. (Scalable means that researchers can make small batches or large batches using the same exact same techniques).

To do this, we built a benchtop reactor system out of a number of common laboratory items and inexpensive, commercially-available components. It turned out that to build our version 1.0 reactor, all we needed was a pump, tubing, and some small plastic connectors that most chemistry labs probably  have already.

In a typical “batch” chemical synthesis, you mix chemicals in a flask to make a new product, but you have to do that mixing over and over when you want to make more. Having to mix a new batch every time means that it can be hard to consistently control the particle properties. By synthesizing our nanomaterials in an automated reactor instead, we can easily increase our nanoparticle output without losing control over our nanoparticles’ properties like size and shape, because we can mix small volumes of chemicals continuously. Just by running a single benchtop reactor continuously, we can now make a gram of high quality nanoparticles in as little as several hours of operating time. If we “number up” our reactors (run several reactors simultaneously), we have the potential to increase our nanoparticle production yields tremendously. The Murphy Group makes nanoparticles for many of the groups in the CSN. By using our new benchtop reactor we can much more easily meet the nanoparticle needs of all our collaborators, who often need very concentrated solutions of gold nanoparticles for biological and toxicological testing.

In addition to allowing users to make larger quantities of nanoparticles, our benchtop reactor allows us to synthesize nanoparticles with minimal waste. The reactor is equipped with an observation window that allows users to monitor nanoparticle quality using absorbance spectroscopy, which means we can terminate runs immediately if the nanoparticles are not up to our usual standards. This minimizes wasted materials, and makes for a greener approach to nanoparticle synthesis. The reactor can also directly interface with several rapid and efficient nanoparticle purification approaches.

For this paper, we initially demonstrated the synthesis of gold nanoparticles in the benchtop reactor, but we expect that the reactor is suitable for the synthesis of many different types of nanomaterials that are typically synthesized in water. We certainly can’t yet use our reactor to synthesize high-quality nanomaterials on the kilogram scale like other, more traditional chemicals; however, we do hope that our simple reactor design will inspire a variety of researchers to use reactors for high-quality, gram-scale nanoparticle synthesis.

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REFERENCES (some may require subscription to access)

1. Lohse S.; Eller J.; Sivapalan S.; Plews M.; Murphy C. A Simple Millifluidic Benchtop Reactor System for the High-Throughput Synthesis and Functionalization of Gold Nanoparticles with Different Sizes and Shapes.” ACS Nano, 2013, 7, 4135-4150. http://dx.doi.org/10.1021/nn4005022
2. Matus K.; Hutchison J.; Peoples R.; Rung S.; Tanguay R. Green Nanotechnology Challenges and Opportunities. ACS Green Chemistry Institute White Paper, June 2011, www.acs.org/greenchemistry.

More information on the benchtop reactor can be found in:
US Patent Application 13/950,726 “Continuous Flow Reactor and Method for Nanoparticle Synthesis” TF12093-US