Handheld Device for Saliva Pretreatment to Improve Cortisol Detection

Salivary cortisol detection offers a noninvasive alternative to blood-based analysis. However, its practical implementation remains limited by the intrinsic viscosity of saliva and the presence of interfering components. In particular, mucins and salivary proteins impede capillary-driven flow and compromise the reliability of subsequent lateral flow assays (LFAs), thereby necessitating effective and accessible pretreatment strategies. Here, we present a handheld saliva pretreatment device, termed SaliFilter, for point-of-care cortisol detection. The device employs a filtration mechanism that selectively removes high-molecular-weight interfering components while allowing the passage of small molecules, including cortisol. Operated by simple manual pressure, it enables rapid sample processing (~2 min) without the need for external equipment, making it suitable for decentralized settings. The performance of the device was evaluated using turbidity measurements, protein quantification, and SDS-PAGE, which confirmed efficient removal of mucin and salivary proteins. Treated samples exhibited enhanced capillary flow, resulting in stable and reliable LFA operation. Quantitative analysis demonstrated improved signal reproducibility, and cortisol detection achieved a limit of detection of 1.47 ng mL⁻¹ over clinically relevant concentration ranges. This protocol establishes an effective saliva pretreatment strategy that improves analytical sensitivity and reliability without compromising analyte integrity. The proposed approach provides a practical, portable solution for saliva-based diagnostics, with potential applicability for point-of-care testing and self-monitoring.