Fluorescence of nanodiamond cocktails: pH-induced effects through interactions with comestible liquids

•The stability of NV-rich carboxylated nanodiamond in comestibles was investigated.•pH dependence of the ND-NV fluorescence is tuned by deprotonation of –COOH groups.•Lemon juice boosts ND fluorescence by increasing electrical conductivity.•Beetroot juice causes strong fluorescence extinction attributed to the betanin presence.•ND reduces surface tension, mostly due to the Brownian motion in the comestibles. Fluorescent nanodiamonds with nitrogen-vacancy centers have become important nanoscale probes for sensing and imaging. The surface chemistry of the nanodiamonds influences their emission, interactions, and quantum properties. In this work, we propose to utilize fluorescent nanodiamonds as photostable markers for investigation of comestible liquids. We prepared nanodiamond/comestibles suspensions/cocktails with a wide range of pH levels and studied the samples via fluorescence, wettability, and zeta potential. The composition of the created cocktails revealed a strong impact on the properties of the nanodiamond and its surface chemistry, mainly induced by pH but also tuned by specific quenching compounds. Moreover, the stability of the nanodiamonds in the cocktail media was studied, along with various nature-originated compounds influencing their surface termination, polarity, and charge states. Thanks to the stability and biocompatibility of the nanodiamond, it can be applied in monitoring the condition of foodstuffs, and in the detection of toxins and pathogens in them.