Design and validation of a plasmon-based colorimetric nanosensor for the sensitive/selective detection of safranal and preventing adulteration of saffron

This work presents a novel colorimetric platform for safranal (SAF) detection using plasmonic nanosensors (PNS) composed of bacterial cellulose nanofibers (BCNF) functionalized with silver nanoparticles (AgNPs) and single-layer graphene oxide (GO). Synthesized GO exhibited an average thickness of 0.9 nm. BCNF, with a 35 nm diameter and ˃10 µm length, demonstrated robust mechanical strength (198 MPa) and thermal stability (300 °C). A control sensor (AgNP-only PNS) was fabricated using AgNPs derived from 0.1% silver nitrate, confirmed by UV-Vis spectroscopy with a localized surface plasmon resonance (LSPR) peak at 450 nm. For enhanced performance, BCNF were treated with GO (25-100 μg/mL) and immobilized with AgNPs (PNSG1-PNSG4). These GO-integrated sensors (PNSG series) displayed superior tensile strength (1.25–1.29 GPa) and Young’s modulus (173–187 MPa) compared to AgNP-only counterparts. Exposure to SAF (1–25 μL, 19.32–483 ppmv) over 12–72 h induced quantifiable color shifts analyzed via CIELab ΔE values. ΔE increased linearly with SAF concentration, plateauing near ΔE ≈ 10. Among all sensors, PNSG1 achieved the lowest limit of detection (LOD = 9 ppmv, RSD = 12.29%), outperforming the Ag-only sensor (LOD = 14 ppmv, RSD = 11.41 Selectivity tests revealed distinct responses: the Ag-only PNS yielded ΔE = 4.53 (acetic acid), 6.3 (acetaldehyde), and 7.33 (SAF), while PNSG1 showed enhanced discrimination with ΔE = 10.03 (SAF), 8.55 (acetaldehyde), and 7.66 (acetic acid). PNSG1 combines exceptional flexibility, mechanical resilience, and sensitivity for SAF detection, making it a promising tool for non-destructive food quality assessment, especially in verifying saffron purity and identifying adulterants.