Direct Use of a Saliva-Collected Cotton Swab in Lateral Flow Immunoassay for the Detection of Cotinine.

The detection of salivary cotinine is useful for convenient smoking tests in spite of the high background effect of saliva. For precise results, the conventional salivary cotinine analysis for smoking detection requires complex pretreatment processes. Hence, in this study, we developed a modified paper-based lateral flow immunoassay (LFIA), termed "gap-LFIA", for the direct application of saliva collected using cotton swabs for on-site detection. The gap-LFIA was constructed by modifying a conventional LFIA sensor, where the sample pad was divided to have a 3 mm gap. A saliva-collected cotton swab was inserted into the gap, and then, a buffer solution was added to the outer sample pad to dilute the saliva automatically. The gap-LFIA reduced the interference in salivary samples and showed improved signals, allowing for using the whole saliva directly without additional steps. Further, the deviation of results using a strip was less than that when the saliva was not diluted in a conventional cotinine kit, and it helped to distinguish between smokers and non-smokers more clearly in 15 min. This method of automatic dilution may apply to various clinical samples, including blood and serum, for direct application in future detections.