A Novel Capsule-Based Smell Test for Diagnosis of Neurological and Respiratory Diseases

To aid in diagnosing diseases where loss of the sense of smell is a symptom, such as in chronic neurological conditions like Parkinson's and Alzheimer's diseases and in acute respiratory infections such as that caused by COVID-19, a team of researchers at Queen Mary University of London (United Kingdom) developed a novel smell testing kit based on capsules of aromatic oils placed between two strips of single-sided tape.

This smelling test was made up of aromatic oil capsules that were prepared by a fabrication technique, which enabled full control over the capsule size, the shell thickness, and the volume of the encapsulated oil. The technique generated capsules by concentrically dripping oil/alginate droplets from a coaxial nozzle into an oppositely charged ionic liquid. After formation, liquid capsules were left to dry and form a solid crust surrounding the oil.


The prototype test used in the current study consisted of placing a standardized number of capsules between adhesive strips that users crushed and pulled apart to release the smell. In addition, a simple mathematical model was developed to predict the volume of encapsulated oil within the capsule in terms of the flow rate ratio and the nozzle size.

In this preliminary study, a small group of eight patients with Parkinson's disease were instructed to crush the capsules between their fingers and then peel back the tape strip to release the aroma contained within the capsules.

The participants reported that the smells from the tests were detectable and remarked on the relative ease of rupturing the capsules, particularly for those with tremors, compared to the standard scratch and sniff smell test available on the market.

First author Dr. Ahmed Ismail, a lecturer of fluid dynamics at Queen Mary University of London, said, "Most of the smell tests on the market depend on using paperboard items treated with a fragrant coating called scratch and sniff, in which you need to scratch a card to release the odor. The problem with this approach is that the amount of odor released depends on the extent to which the individual scratches, something that might affect the outcome of the test. Our capsule-based smell test does not have this problem because the amount of odor released is controlled by the amount of oil precisely encapsulated. The mass-production of our new test would also be cheaper than a scratch and sniff test.

Dr. Ismail said, "Our capsule-based smell test can assist in the rapid diagnostic of various diseases linked to the loss of smell. These include chronic neurological conditions such as Parkinson's and Alzheimer's disease, as well as COVID-19, which is known to affect the sense of smell. Being non-invasive and less stressful, the capsule-based smell test has benefits over the nose swab in diagnosing COVID-19. This is an advantage for testing children in particular, as they are typically horrified if they need to do a nose swab, and the test can be done in the comfort of their own home."

The capsule-based smell test was described in the April 28, 2021, online edition of the journal Royal Society Interface.

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