Artificial Olfactory Systems in the Diagnosis of Neurodegenerative Diseases

Neurodegenerative diseases form a group of nervous system disorders characterized by a prolonged latent stage, a wide range of manifestations linked to the heterogeneity of symptoms, varying levels of disease aggressiveness, and progressive neuronal death. Clinical data, alongside expensive invasive and noninvasive imaging techniques, primarily form a basis for diagnosing neurodegenerative diseases. There is no specific laboratory test available for their diagnosis. Exhaled breath represents a bodily secretion, and its collection is both simple and cost-effective. The analysis of exhaled gases is an inexpensive and a noninvasive method for detecting a wide range of diseases, including neurodegenerative disorders. Molecular profiles of volatile organic compounds in an exhaled breath, relevant for diagnosing various neurodegenerative diseases, can be obtained through human breath analysis using an “electronic nose.” Identifying volatile organic compounds and utilizing them as specific biomarkers for neurodegenerative diseases offers a precise, reproducible, and rapid diagnostic alternative to conventional invasive methods. This review focuses on the challenges and achievements of the last decade (2014–2023) in applying the electronic nose technology to the detection and identification of potential volatile organic compounds associated with neurodegenerative processes. It highlights studies on the detection of potential volatile organic compounds in the exhaled breath of patients with Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, and amyotrophic lateral sclerosis using an electronic nose and gas chromatography–mass spectrometry. The review discusses trends in the development and application of the electronic nose technology to medical care, enabling the precise and sensitive detection of key volatile organic compounds in an exhaled breath.