Quantifying GNP-glycan-DC-SIGN/R binding affinity. GNPs are well-known for their strong and universal quenching property for a range of different fluorophores. Moreover, its quenching efficiency (QE) -distance dependence has been shown to follow the nano-surface energy transfer (NSET, where QE is proportional to the inverse 4 th power dependence on distance), rather than the Förster resonance energy transfer (FRET, where QE is proportional to the inverse 6 th power dependence on distance) mechanism experienced by organic quenchers. As a result, its quenching is far more efficient and able to cover a longer distance range than those relying on the FRET mechanism. Indeed, the GNP's superior quenching ability has been widely exploited for biosensing, bioimaging and biodiagnostic applications. Recently, we have demonstrated that GNP's outstanding fluorescence quenching can be harnessed as a new readout method for quantifying MLGI affinities using a small G5-glycan (Fig. ). In that case, we first introduced a site-specific cysteine mutation on the CRD of the DC-SIGN/R extracellular segment. The mutation site lies at close to, but outside of, its glycan binding pocket, and therefore does not affect its glycan binding property.