Smartphone-assisted detection of Bi³⁺ ions using a calix[4]arene-based fluorescent sensor from cosmetics and water...

Bismuth (Bi³⁺) contamination has become an important concern in environmental and cosmetic safety studies. Bismuth compounds are widely used in cosmetic formulations such as compact powders and eyeshadows because of their pearlescent appearance, smooth texture, and skin-adhesive properties. Bi³⁺ ions may enter environmental water systems through industrial effluents, mining activities, and improper disposal of chemical wastes. This contamination can affect natural water bodies such as lakes, rivers, and tap water supplies, potentially impacting aquatic organisms and human health.

In this work, we designed a fluorescence sensor capable of detecting Bi³⁺ ions with high sensitivity and portability. The fluorescence sensor was developed based on calix[4]arene functionalized with cystamine dihydrochloride linkage and dansyl acid used as a fluorophore (C4ADA). C4ADA exhibits high selectivity towards Bi³⁺, resulting in a marked fluorescence enhancement attributed to a chelation enhanced fluorescence (CHEF) mechanism. The sensor exhibited a linear fluorescence response over the Bi³⁺ (0-80 nM), with a detection limit of 8.7 nM. To demonstrate real-world applicability, the performance of C4ADA was examined in different types of samples via fluorescence methods, such as compact powder, eyeshadow, industrial water, lake water and tap water samples.

Bi³⁺ detection was successfully demonstrated using a disposable paper-based sensor integrated with a smartphone, where fluorescence color changes were quantified through RGB analysis of C4ADA, compact powder, and eyeshadow, yielding a LOD of 19.5 nM to 22.4 nM. Due to its low cost, simplicity, and portability, this method is suitable for on-spot monitoring of Bi³⁺ ions.