Counterfeit drugs pose a major health problem, particularly in the developing world. Available technologies to identify such fakes are both expensive and require expert technicians, neither of which are readily available in these regions.

A simple and affordable device that differentiates drugs based on the density of any liquid was designed at the University of California, Riverside. The counterfeit catcher is based on a 3,000-year-old African musical instrument. The mbira sensor can be assembled from off-the-shelf or discarded materials and could offer pharmacists and consumers inexpensive protection from counterfeit and adulterated drugs.

The researchers observed that frequencies of sound created by a musical instrument are governed by the Mbira musical instrument, left, next to a density sensor based on it. Source: William Grover/University of California, Riversideinstrument’s physical properties, such as the length or tension of a guitar string. But could adding a sample of interest to an instrument and measuring changes in notes be of value in defining the sample’s properties?

A mbira, or kalimba, made of graduated metal prongs attached to a soundboard, was modified by replacing the prongs with bent metal tubing and injecting it with a liquid. The frequency of the musical notes made by the filled and empty tube was compared to measure the liquid’s density. When empty, the tube played a G sharp note, and when filled with water it emitted an F sharp.

A new device constructed from scrap wood and tubing was tested, revealing that the optimal mbira sensor tube had thin walls and a length no shorter than 50 mm. Its application to the detection of counterfeit drugs was next evaluated, starting with the differentiation between harmless glycerol and poisonous diethhylene glycol in cold medicines.

After filling the sensor with each substance, recording its musical output with a smartphone and uploading the recordings to an analysis website, glycerol and diethylene glycol were shown to generate notes whose frequencies differ by 10 Hz.

Six different batches of a popular cold and flu medicine purchased locally from different pharmacies made the same musical note when loaded into the sensor, suggesting that the medicines were identical and authentic. Any sample of the drug associated with a different musical note must be chemically different from the authentic drug and may be counterfeit or adulterated.

The research is published in ACS Omega.