High-performance Sn/AuNP-based spectroscopic ellipsometric sensor for patulin

A label-free spectroscopic ellipsometric (SE) aptasensor was developed for ultra-sensitive patulin (PAT) detection on a tin (Sn) substrate modified via electrochemical grafting of a 4-mercaptobenzene diazonium-derived self-assembled monolayer. Cyclic voltammetry and high-resolution X-ray photoelectron spectroscopy confirmed uniform nanofilm formation, followed by citrate-reduced gold nanoparticle decoration and thiolated anti-PAT aptamer immobilization. Monitoring the ellipsometric phase shift (Δ) at 507 nm and 508 nm yielded linear responses over 0.01-1000 ng/mL PAT (R² > 0.98) with limits of detection of 10.7 pg/mL and 9.5 pg/mL (3.3 σ), respectively. Isotherm fitting indicated pseudo-second-order binding (R² = 1.00), consistent with surface-constrained, mass-transfer-limited interactions. Precision (%RSD <1.1 %) and accuracy (%RE within ±5 %) were validated in both buffer and spiked apple-juice samples (recoveries 98.9-103.2 %). This label-free SE approach combines a wide dynamic range and sub-10 pg/mL sensitivity with minimal sample preparation and no external labels.