Nanoscale GO–AgNPs/CMC Films for Food Safety Monitoring: Dual-Mode Optical Sensors for Brilliant Blue Detection

The development of nanoscale multifunctional sensing platforms for food safety monitoring has gained much interest in recent years. Here, we present a dual-mode optical sensor based on a graphene oxide–silver nanoparticle (GO–AgNP) nanocomposite dispersed in a biodegradable carboxymethyl cellulose (CMC) film for selective detection of Brilliant Blue FCF (BB) dye. The nanoscale dispersion of GO sheets and AgNPs in the polymer matrix introduces high surface area, intense π–π stacking, and surface plasmon-coupled fluorescence quenching that synergistically enhance the sensing properties. The nanocomposite showed cyan fluorescence emission under UV irradiation with bands at 469 and 546 nm that were progressively quenched by BB through static interactions and inner filter effects (IFE), giving a “turn-off” fluorometric response. Concurrently, a characteristic colorimetric shift from pale brown to bluish-green supported naked-eye identification. The sensor exhibited an extensive linear range (1 nM to 25 μM) and low detection thresholds of 0.321 μM (fluorescence) and 1.886 μM (colorimetry), along with excellent selectivity against structurally related dyes and ionic interferents. Smartphone-based HSV (Hue, Saturation, Value) analysis also facilitated portable and semiquantitative confirmation. Excellent recoveries (97.2–104.3% recovery, relative standard deviation (RSD) < 3.6%) were obtained from real sample recovery studies in drinks and candies. These results highlight the viability of the GO–AgNP/CMC nanocomposite film as a cost-effective, disposable, and environmentally friendly nanoscale platform for applicable food safety screening of artificial coloring agents.