Luminescence "Turn-On" Detection of Gossypol Using Ln³⁺-Based Metal-Organic Frameworks and Ln³⁺ Salts

Gossypol (Gsp), a natural toxin concentrated in cottonseeds, poses great risks to the safe consumption of cottonseed products, which are used extensively throughout the food industry. In this work, we report the first luminescence "turn-on" sensors for Gsp using near-infrared emitting lanthanide (Ln³⁺) materials, including Ln³⁺ MOFs and Ln³⁺ salts. We first demonstrate that the Yb³⁺ photoluminescence of a Yb³⁺ MOF, Yb-NH₂-TPDC, can be employed to selectively detect Gsp with a limit of detection of 25 μg/mL via a "turn-on" response from a completely nonemissive state in the absence of Gsp. The recyclability and stability of Yb-NH₂-TPDC in the presence of Gsp was demonstrated by fluorescence spectroscopy and PXRD analysis, respectively. A variety of background substances present in practical samples that would require Gsp sensing, such as refined cottonseed oil, palmitic acid, linoleic acid, and α-tocopherol, did not interfere with the Yb³⁺ photoluminescence signal. We further identified that the "turn-on" of Yb-NH₂-TPDC photoluminescence was due to the "antenna effect" of Gsp, as evidenced by spectroscopic studies and supported by computational analysis. This is the first report that Gsp can effectively sensitize Yb³⁺ photoluminescence. Leveraging this sensing mechanism, we demonstrate facile, highly sensitive, fast-response detection of Gsp using YbCl₃·6H₂O and NdCl₃·6H₂O solutions. Overall, we show for the first time that Ln³⁺-based materials are promising luminescent sensors for Gsp detection. We envision that the reported sensing approach will be applicable to the detection of a wide variety of aromatic molecules using Ln³⁺ compounds including MOFs, complexes, and salts.