A low cost, portable optical sensing platform enables rapid and sensitive detection of methyl salicylate (MeSal) in unprocessed samples. The sensing assay is based on a strong photoluminogenic response when MeSal forms a complex with a terbium cation (Tb3+) in aqueous buffer. The assay employs an airtight three-well sensing chamber that allows the volatile MeSal to spontaneously diffuse out of a sample well and partition into a neighboring test well where the intense green Tb-photoluminescence is detected by the naked eye or a cell phone camera. This MeSal vapor diffusion process mimics the biological airborne messenger mechanism used by distressed plants to warn their neighbors and prompt a communal defense. Within the assay chamber, the MeSal vapor diffusion acts as a purification step that separates the MeSal photoluminescent signal from the interfering sample background signal. Proof-of-concept experiments show that the optical assay can quickly distinguish a sample of commercial toothpaste that contains 0.48% MeSal from a sample that does not contain MeSal. This type of high-throughput semi-quantitative screening is increasingly mandated by regulatory agencies who have placed upper limits on the amount of added MeSal within cosmetic products. Practical utility for enzyme detection is also demonstrated by using a novel substrate molecule, MeSal-Glc, to detect the presence of the flavor-promoting enzyme β-glucosidase in almond flour, a representative food sample. Many other enzyme detection assays can likely be developed using bespoke substrate molecules that contain MeSal as a releasable reporter unit for Tb-photoluminogenic sensing.
Shi et al. (Thu,) studied this question.