The sense of smell is crucial for health and well-being, and its dysfunction significantly impacts quality of life, potentially affecting mental and physical health, social interactions, and safety. Smell dysfunction is also a biomarker for neurological diseases like Alzheimer's and Parkinson's. Current smell tests, like those using multiple sniffing pens, are time-consuming and require specialized personnel, hindering widespread use. Olfactometers offer automation but are expensive, bulky, and lab-bound. This research addresses this need by developing a portable, affordable, and user-friendly odor delivery device to facilitate efficient and widespread smell testing.

Existing smell tests utilize various approaches, including multiple felt-tip pens with serial odorant dilutions manually presented by nurses, which are time-consuming and complex. Olfactometers, while offering automated odor delivery, are often costly, bulky, and confined to laboratory settings due to their complex components (pumps, temperature-controlled reservoirs, valves, and mass flow controllers). Miniaturized odor delivery devices exist, but they often compromise performance in terms of odor flow control, intensity, directivity, temporal resolution, contamination, and flexibility, limiting their clinical and research applications. Therefore, a compact, time-efficient, and flexible system was needed to enable effective smell testing across diverse settings.

The researchers designed a portable, multi-channel odor delivery device capable of delivering 24 odors simultaneously. The device uses a diaphragm pump to draw and filter air, which is then directed to 24 solenoid valves connected to individual odor reservoirs within a removable cartridge. Liquid odorants are absorbed onto sponges within these reservoirs. Airflow rates can be adjusted (2–6 L/min), and up to three channels can be activated simultaneously. The system is digitally controlled by a microcontroller board with Bluetooth connectivity, enabling mobile application control and data logging. A mobile app facilitates odor delivery triggering and collects user perceptual feedback via a questionnaire. The device was characterized for airflow rate uniformity, odor intensity repeatability and stability (using a photoionization detector), and spatial odor distribution. A test-retest reliability and accuracy study was conducted using the device for administering a customized SMELL-S olfactory threshold subtest, comparing it to the standard Sniffin' Sticks test with 37 healthy subjects and 31 patients with smell loss.

Device characterization revealed consistent airflow rates across channels (<5% deviation from the mean of 3 L/min). Odor intensity showed good short-pulse repeatability (<4.2% RSD) but decreased with continuous activation due to reservoir depletion. Spatial odor distribution demonstrated a rapid intensity drop with distance from the outlet, highlighting the need for precise user positioning. Temperature stability showed a 5% °C⁻¹ coefficient. The clinical study comparing SMELL-S (using the new device) to Sniffin' Sticks demonstrated a significant reduction in test completion time: median 6 min (IQR = 3) for SMELL-S versus 14 min (IQR = 9) for Sniffin' Sticks (p<0.0001, Mann-Whitney test).

The developed device successfully addresses the limitations of current smell testing methods by offering a portable, affordable, and user-friendly alternative. The significant time reduction in the SMELL-S test compared to Sniffin' Sticks highlights the efficiency gains from automation and self-administration, minimizing human error. The device's digital integration allows for streamlined data collection, further enhancing efficiency. While the study demonstrates the device's technical feasibility and potential for improved testing efficiency, further clinical validation of the SMELL-RS test using this device is needed to confirm its clinical utility and ensure its reliability for diagnosing olfactory disorders.

This research introduced a novel portable, multi-channel odor delivery device for rapid and self-administered smell testing. The device demonstrated high temporal precision, minimized cross-contamination, and significantly reduced test administration time compared to existing methods. Further clinical validation is warranted to establish its effectiveness as a diagnostic tool. Future research could explore modifications for broader applications and integration with other diagnostic platforms.

The study's sample size, while sufficient for demonstrating significant time differences, may not be fully representative of diverse populations. The spatial distribution of the odor stream necessitates accurate user positioning, which may need additional attention in future designs or usage instructions. Further investigations are also necessary to fully validate the device's clinical utility in diverse settings and populations.