Counterfeit medicines are a risk to public health and safety, especially in low- and middle-income countries. The rise of online pharmacies has resulted in increased production of counterfeit lifestyle drugs and lifesaving drugs. It's estimated that counterfeit medicines account for 10% of the global pharmaceutical trade.

A number of approaches can detect counterfeit medicines; these traditionally include determining the chemical signatures of major ingredients with the assistance of analytical chemistry and spectroscopy technologies. More recently, manufacturers can modify the surface or coating of tablets and capsules to provide unique markings and printings on medicines.

Other manufacturers are using package-level barcodes with radiofrequency identification (RFID) to authenticate medications. Other technologies such as QR-coded tags or QR printing are available. However, the ideal candidate to provide security would provide on-dose protection and validation, as well as be safe for consumption.

In the current study, the researchers propose the use of physically unclonable functions (PUFs) as high security on-dose authentication. This technology provides a digital fingerprint and is extremely challenging to clone. PUFs generate a unique output each time they are stimulated by an external input, and they generate a different response each time they are stimulated. This means that even the manufacturer cannot duplicate the tag.

"Every single tag is unique, offering a much higher level of security," said Young Kim, PhD, an associate professor in Purdue's Weldon School of Biomedical Engineering.

The PUFs are composed of silk proteins that are genetically fused with different fluorescent proteins. Silk proteins are both edible and digestible, and they are also available in both nano- and microscale structures for manufacturing. The fluorescent proteins used include enhanced cyan fluorescent protein (eCFP), enhanced green fluorescent protein (eGFP), enhanced yellow fluorescent protein (eYFP), and mKate2 (far-red) fluorescent protein. The particulate silk proteins are embedded in a thin film that can be directly attached to the surface of a solid-dose medication.

When light is exposed to the PUF, the fluorescent silk microparticles are excited and emit cyan, green, yellow, or red fluorescent patterns. These patterns generate a unique digitized key that can then be authenticated.

With PUF technology, end users can verify the authenticity of the medicine by using the built-in flashlight LED and camera of a smartphone. Pharmacies can confirm the medicines with a customized reader that validates the digital key in a secure online cloud server.

"Our concept is to use a smartphone to shine an LED light on the tag and take a picture of it. The app then identifies if the medicine is genuine or fake," said Jung Woo Leem, PhD, a postdoctoral researcher in biomedical engineering at Purdue.

The researchers determined that the PUF tags work for at least a two-month period before the proteins begin to degrade. The next goal is to confirm that the tag can last as long as the active drug ingredients so that it does not affect the medicine's potency.

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