Europium(III)-driven red photoluminescent sensor for ultra-sensitive and reliable assay of sildenafil citrate in pure form, pharmaceutical formulations and Bio-fluids
Abstract
Lanthanide complexes, particularly Eu3+ β-diketonates, offer narrow-band, long-lived red emission ideally suited to sensitive fluorescence assays in complex media. The Eu(TTA)3(H2O)2 chelate combines efficient near-UV excitation, robust emission and labile coordination sites, making its signal highly responsive to molecular binding events. Sildenafil citrate is a widely used PDE-5 inhibitor whose misuse, counterfeiting and potential drug interactions demand reliable monitoring in pharmaceuticals and biological fluids. However, current chromatographic techniques are costly and labor-intensive, creating a pressing need for a simple, robust, low-cost, green, field-deployable optical method for sildenafil quantification. Near-UV excitation around 350 nm efficiently promotes ligand-to-metal energy transfer to the Eu3+ 5D0 level, producing line-narrowed 5D0→7F2 emission at ∼ 614 nm whose intensity is selectively quenched by sildenafil without disturbing its spectral fingerprint. The interaction between the Eu-TTA chemosensor and sildenafil involves a mixed mechanism of dynamic fluorescence deactivation and static "antenna" shelving, governed by photo-induced electron transfer and triplet-triplet energy transfer. Under optimized experimental conditions, the sensing protocol exhibits excellent linear Stern-Volmer behavior for sildenafil concentrations from 0.2 to 8.0 µg mL-1 (r ≈ 0.999), with a limit of detection of 0.036 µg mL-1 and a limit of quantification of 0.121 µg mL-1.…
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