NHS-ester conjugated gold nanoparticles for spermine detection: a potential tool in meat spoilage monitoring†

Spermine, a key biogenic amine indicating food freshness, is typically detected using costly and time-consuming chromatographic methods. This study introduces a more efficient, eco-friendly alternative—a label-free colorimetric sensing platform using gold nanoparticles (AuNPs) functionalized with 11-mercaptoundecanoic acid and capped with an N-hydroxysuccinimide (NHS)-ester. Transmission electron microscopy revealed monodisperse, spherical AuNPs (13 nm), with an increase in size upon functionalization. Fourier transform infrared spectra confirmed successful functionalization. The hydrodynamic size of the AuNPs increased from 17.26 nm to 2167 nm, and the zeta potential shifted from −48.86 mV to −35.59 mV. The platform takes advantage of the selective interaction between spermine and NHS-ester-functionalized AuNPs, inducing nanoparticle aggregation, as shown by a red shift in surface plasmon resonance (SPR). UV-vis spectroscopy demonstrated a robust linear correlation (R² = 0.958) between spermine concentration (1.0–4.0 μM) and nanoparticle aggregation index, with a limit of detection (LOD) of 0.77 μM. The sensor also exhibited high reproducibility in pork extract matrices (coefficient of variation <5%) and selectivity for spermine amid various interfering analytes. Its eco-friendly design and rapid response time position it as a viable tool for real-time spermine monitoring in food spoilage, offering comparable performance metrics to traditional chromatographic techniques while addressing sustainability concerns.