A Portable 3D Microfluidic Origami Biosensor for Cortisol Detection in Human Sweat

Analysis of cortisol levels in human sweat is increasingly important as it can be a "stress biomarker" in stress-related disorders, giving real-time information about human health status. In this study, a portable 3D microfluidic origami biosensor based on a smartphone was developed for cortisol-level detection in human sweat. Molybdenum disulfide (MoS₂) nanosheet-mediated fluorescence resonance energy transfer (FRET) and fluorescently labeled aptamers were employed in the biosensing process. A multilayer-structured 3D origami microfluidic chip was fabricated and functionalized to facilitate low-volume perspired human sweat collection, transportation, and detection. The translatability of the biosensor was exhibited by the fluorescence analysis in a smartphone mounted in a custom-designed holder. The critical design parameters of the microfluidic origami biosensor, including the characterization of various paper substrates, the concentration of MoS₂ nanosheets, and the incubation/reaction time, were adjusted to obtain an acceptable range for the assay dynamic range and limit of detection (LOD). Under optimum conditions, various doses of cortisol within the physiologically relevant range of 10-1000 ng/mL reported in human sweat were tested to evaluate the performance of the proposed biosensor. It displayed an LOD of 6.76 ng/mL at 3σ in artificial sweat, an analysis time of 25 min, and high selectivity. The performance of the proposed cortisol sensor was compared with an enzyme-linked immunosorbent assay (ELISA) for a spiked artificial sweat sample, and a correlation coefficient of 0.988 was found. The proposed biosensor also presented satisfactory results in the determination of the cortisol levels in a real human sweat sample. The resulting portable biosensor provides a rapid, low-cost, convenient, and non-invasive sensing solution for the point-of-care analysis of cortisol levels in sweat.