A portable front-face fluorescence-sensing platform based on thiourea-Schiff-base for rapid, on-site detection of hazardous mercury contamination in whitening cosmetics

Developing methods for directly detecting mercury (Hg²⁺) in real samples without any pretreatment remains a significant challenge in analytical chemistry. In this study, we developed a portable front-face fluorescence system (PFFFS), a simple, rapid, and highly practical method that requires only the mixing of the sample with the pre-prepared reagent kit for immediate testing, requiring no sample pretreatment, weighing, or digestion, enabling on-site Hg²⁺ detection in whitening cosmetics. We systematically investigated the effects of pH, reaction time, interfering ion masking agents, and fluorescent probe stabilizers on the measurement of Hg²⁺. To mitigate memory effects caused by Hg²⁺ contamination, single-use disposable reagents and consumables were designed. The correlation between actual Hg²⁺ content (measured by ICP-MS) and fluorescence intensity obtained from PFFFS was utilized to effectively reduce matrix interference. Under optimal conditions, the method had a detection limit of 6.8 mg/kg and a linear range of 23.2-4429 mg/kg. The proposed method was successfully applied to detect Hg²⁺ in 216 whitening cosmetics, including various creams, lotions, and essences lotion, with results consistent with those obtained from ICP-MS analyses. Compared with conventional analytical techniques, the PFFFS method offers distinct advantages such as lower cost, shorter detection time (6 min), portability, and suitability for consumer self-testing. This PFFFS approach can serve as an early warning tool for high Hg²⁺ contamination before routine laboratory testing, protect sensitive laboratory instruments, and enhance consumer safety by enabling rapid on-site screening of potentially hazardous cosmetics. Furthermore, by facilitating timely detection and control of Hg²⁺ exposure, this method contributes to reducing environmental contamination and associated human health risks.