Colorful microparticles for anticounterfeiting

Glowing, smartphone-readable nanocrystals could authenticate products

Lime green, yellow, bright blue—these are among the colors combined in the distinctive stripe patterns that glow on the smartphone held by MIT postdoc Jiseok Lee after he takes a photo of the pharmaceutical blister pack sitting on his lab bench. Some stripes contain six colors, others three or four. Each sequence of colors is readily distinguishable on the screen. But without the near-infrared light source and 20× magnifying lens attachments on his smartphone, these stripes, approximately 200 µm long, are invisible to the naked eye. The blister pack appears ordinary; there are no signs that a serial number–like identifier has been encoded onto its surface.

“The glowing stripes are microparticles made of nanocrystals doped with rare-earth metals known for their unique magnetic, luminescent, and electrochemical properties,” explains Lincoln Laboratory biomaterials scientist Albert Swiston, who manufactured the microparticles with Lincoln Laboratory colleague Paul Bisso, MIT chemical engineering professor Patrick Doyle, MIT postdoctoral researcher Jiseok Lee, and MIT graduate students Rathi Srinivas and Jae Jung Kim. The researchers used sodium yttrium fluoride (NaYF4) nanocrystals, which emit visible light when they are subtly doped with lanthanides (a subset of the rare-earth metals) and then irradiated with near-infrared light. “By adjusting the doping ratios of ytterbium, erbium, thulium, and other lanthanides, we are able to tune the crystals to emit any color in the visible spectrum,” says Bisso. So far, nanocrystals have been created in nine distinct colors, though the exact number of distinguishable colors is limited primarily by the sensitivity of the detector (in this case, a smartphone).

iPhone showing REMcodes glowingAn iPhone 4S, equipped with a magnifying lens and near-infrared light source, acquires an image of Rare-Earth Microbarcodes that have been embedded onto a pharmaceutical blister pack.
To fabricate the microparticles, called Rare-Earth Microbarcodes, the team uses a combination of microfluidics and stop-flow lithography, a technique previously developed by Doyle that enables production of microparticles of diverse shape, size, and chemical composition. The lanthanide-doped nanocrystals are fabricated in scalable processes by mixing rare-earth salts with sodium and fluorine-containing compounds at high temperature. Because of the small size of the finished microbarcode product, relatively small amounts of these nanocrystals (and hence precious rare-earth elements) are needed for full-scale production. Nanocrystals are then dispersed in parallel, laminar streams of an ultraviolet (UV)-curable polymer, such as polyurethane diacrylate, and flowed into a microfluidic device. When pulses of UV light hit the flowing stream, a colorful microparticle composed of a patterned polymer-nanocrystal composite is formed. The particle takes on the tough physical properties of the cured polymer, enabling seamless integration of particles into or onto products manufactured through three-dimensional (3D) printing, hot extrusion, lamination, inkjet printing, stamping, and other industrial processes.
REMcodes microfluidic channelsMicrofluidic channels are loaded with multiple laminar flows, each of which contains nanocrystals that emit different colors, and aligned on a microscope stage. A photomask, which is placed in the eyepiece of the microscope, defines the shape of the UV light beam as it travels toward the stream. In the case shown above, the photomask creates a multirectangular beam that creates several identical striped particles simultaneously. Different photomask patterns yield different shapes that can be imprinted onto the flowing streams in the microfluidic device.

Through this technique, a massive set of microparticles with unique colors, sequences, and spatial positioning can be generated. “One million different color combinations are possible for particles containing six stripes, for example,” says Swiston, alluding to the formula (CN)P, where C is the number of distinct colors (in this case, 10), N is the number of stripes on an asymmetric particle, and P is the number of particles. According to Bisso, there are many ways of orienting the particles in specific configurations. “You can actually draw a picture or write words with them,” he says. If multiple microparticles are deposited into or onto a product, the encoding capacity becomes exponential. Pulling 10 particles at random from a readily manufactured set of 1000 distinct microparticles yields an encoding capacity of 1030 unique signatures—enough to tag every manufactured item on earth many times over.This technique can produce microbarcodes specific to each individual unit (unlike regular barcodes, identical copies of which are assigned to all units of a given product). Stored in a database, these microbarcodes could be used to authenticate products; the unique combination of colorfully striped particles would simply have to be read out with a smartphone camera and matched to its corresponding database entry.

Although many anticounterfeiting technologies exist, a low-cost, secure, exponentially scalable, easy-to-use solution for product authentication is currently lacking. Several technologies—edible microtags, DNA-based and laser-based digital serial codes, and other microparticle color codes—rely on expensive proprietary decoders that must be operated by trained users. While quick-response (QR) codes (two-dimensional square barcodes that can be scanned using a smartphone camera) can encode each item with a unique identity, they can be easily replicated and spoofed on a massive scale. Radio-frequency identification (RFID) tags are more secure than QR codes, but are more expensive to manufacture and require more infrastructure than a smartphone. Unobtrusively incorporating tags or codes into products during the manufacturing process is also problematic for many of these technologies.

Because of these limitations, conventional anticounterfeiting technologies have not been adopted on a widespread scale. The true cost of anticounterfeiting is difficult to measure, so manufacturers have little incentive to incorporate these technologies into their products at the expense of eroding their profit margins. Generally, only high-margin products, such as luxury goods, are seen with anticounterfeiting labels today. Yet counterfeit goods are estimated to account for $1.7 trillion dollars of the global economy.1 By some estimates, two percent of the 26 million airplane parts installed each year are fakes,2 counterfeit medicines represent 10–15% of the world’s drug supply,3 and counterfeiting activities annually generate $250 billion in funds for organized crime.4

REMcodes applicationRare-Earth Microbarcodes can be applied to (left to right, top panel) drug packaging, currency, credit cards, porcelain figures, or artwork, and embedded into 3D-printed plastic. A 1 W 980 nm laser was used to acquire the corresponding barcode images seen in the middle panel. In the absence of near-infrared illumination, the barcodes are covert (bottom panel).

As an ultralow-cost, secure, smartphone-compatible product authentication and serialization technology, Rare-Earth Microbarcodes could transform the anticounterfeiting industry.

  • With the manufacturing cost per code being a fraction of a cent (compared to upwards of $0.05 per code for RFID, for example), commodity industries would be more apt to adopt the technology. These microbarcodes are designed to work with any UV-curable polymer and most nanoscale materials and are thus unhindered by material incompatibilities. Moreover, they can easily be incorporated into or onto products without manufacturers having to adjust their processes or the products themselves and can withstand high temperatures (>300°C), strong solvents, reactive chemicals, mechanical stress, and intense optical illumination with no impact on decoding. For applications that require precise particle placement or efficient particle collection (e.g., transfer printing or integration near the surface of a plastic product), the microbarcodes, which contain the magnetic rare-earth metal gadolinium, can be magnetically manipulated.
  • The smartphone decoder, which will eventually be attachment free because of improvements in the brightness of smartphone light-emitting diodes and the sensitivity of cameras, will enable anyone with a smartphone to image the particles. Consumer participation in product authentication will lead to heightened vigilance against counterfeiting.
  • Although no current anticounterfeiting technology is completely secure against counterfeiters, Rare-Earth Microbarcodes and similar tools that combine technology barriers and serialization force counterfeiters to expend significant resources on copying, stealing, or spoofing product codes or tags. In addition, these microbarcodes are highly inconspicuous; without laser illumination, they are impossible to see. With this technology, the potential exists to use multiple taggants on a single particle, increasing the number of security elements that must be successfully compromised by a counterfeiter. Placing different microbarcodes on individual products (i.e., serialization) enables item-level tracking in the supply chain, making it harder for counterfeiters to produce fakes.
“At Gaming Partners International [GPI], we are always interested in employing the cutting edge in anticounterfeiting technology to ensure our products are maximally secure. This technology has a high encoding capacity and could seamlessly integrate into our poker chip production process. The ability to visualize the particles with a merely modified cellphone is extremely exciting—we know of no other technologies like this in the industry,” says Emmanuel Gelinotte, vice president of global research and development and product development at GPI. 

In the future, Rare-Earth Microbarcodes could be equipped with chemical sensors, becoming “smart” labels that provide not only secure serial numbers to verify product authenticity but also information to monitor product quality and handling. “For example, a temperature sensor could detect if a pharmaceutical drug was ever exposed to temperatures outside of its labeled storage condition,” says Swiston.

Posted February 2016

1 International Chamber of Commerce, Global Impacts Study, available at

2 B.B. Heavner, "Cleared for Knock-Off: Counterfeiting at 30,000 Feet, BlueSky Business Aviation News, 9 Dec. 2010, available at

3 H.I. Miller, "Fake Drugs All at a Pharmacy Near You," Forbes, 16 Feb. 2012, available at

4 U.N. Office on Drugs and Crime, "New UNODC Campaign Raises Consumer Awareness of Links Between Organized Crime and $250 Billion a Year Counterfeit Business," 14 Jan. 2014, available at


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