The azide-alkyne cycloaddition is increasingly popular as an effective strategy for stoichiometric bioconjugation. It offers several advantages over other bioconjugation techniques due to its high orthogonality, biocompatibility, high yields, and rapid kinetics. Metalfree strain-promoted alkyne-azide cycloaddition (SPAAC) has been shown to be an efficient and safe alternative to Cu(I)-catalyzed alkyne-azide cycloaddition (CuAAC), where the final conjugates often contained cytotoxic copper. Both CuAAC and SPAAC have been already exploited on various NPs systems such as quantum dots, as well as polymeric, metallic and metal oxide NPs. The quantification of the dibenzocyclooctyne (DBCO) moiety, widely used as the alkyne in SPAAC, is rather straightforward because of the presence of an absorbance band in the UV range. Nevertheless, a quantitative approach to surface functionalization with azides is often missing. A large portion of the published work still opts for full surface coverage with azide-carrying groups or, if not, rarely reports the actual number of azides per particle.