Edible optical microcavities for optical barcoding, authentication, and sensing

The safety, authenticity, and traceability of food and pharmaceutical products are critical challenges, especially in the context of widespread counterfeiting. Most existing anti-counterfeiting and sensing technologies are applied externally to packaging, making them vulnerable to tampering. A more robust approach is to incorporate them directly into edible products. Whispering-gallery modes (WGMs), highly sensitive optical resonances supported by spherical microcavities, provide a promising platform due to their environmental responsiveness and spectral uniqueness. Here, we demonstrate edible WGM microcavities based on chlorophyll-coated silica microspheres. Monodisperse microspheres exhibit stable WGM resonances under continuous-wave laser excitation, with quality factors ranging from 2,000 to 10,000. Individual microsphere diameters are determined with a precision of approximately 40 nm. When embedded in low-refractive-index agarose matrices, the microspheres generate size-specific spectral signatures that function as optical barcodes and remain stable for at least six months. Based on intrinsic size variations, we further demonstrate edible physical unclonable functions (PUFs) with stable and unique optical identifiers. In addition, the microcavities enable sugar concentration measurements with uncertainties as low as 0.23 percentage points and pH sensing with an accuracy of approximately 0.3 pH units, when embedded in a pH-responsive hydrogel. These results establish edible WGM microcavities as a multifunctional platform for secure labeling, sensing, and anti-counterfeiting in consumable products.