First, a LA-EG4-acetylene linker was synthesised by using the standard dicyclohexyl-carbodiimide /N,N-dimethyl aminopyridine (DCC/DMAP) mediated amide coupling between lipoic acid and H2N-EG4-acetylene. Then, α-1-manno-α-1,2-biose appending an EG2-azide linker (N3-EG2-DiMan, to offer some flexibility to the terminal DiMan group) was synthesised using our established route as described previously. Finally, the LA-EG4-acetylene linker was efficiently coupled to N3-EG2-DiMan or N3-EG2-OH (commercial) via the Cu-catalyzed click chemistry to give the desired LA-EG4-DiMan or LA-EG4-OH ligand in good yields, respectively. Their chemical structures were confirmed by GNP Synthesis and Characterisation. Three different-sized GNPs with an average diameter of ~5, ~13 and ~27 nm (see SI, Figs. S1 and S2 for their TEM images), denoted as G5, G13 and G27, respectively, were employed in this study. Our motivation here was that tuning the GNP scaffold size may lead to an optimal glycan-GNP with excellent spatial and topological match to DC-SIGN/R, thereby greatly enhancing their MLGI affinity and selectivity with the target lectins. The GNPs were either purchased commercially (for G5) or synthesized in house (for G13 and G27) via the literature protocols with minor modifications as described in the experimental section. Interestingly, the LA-EG4-DiMan ligand coated G5 particle (denoted as G5-DiMan) has a similar size and mannose coating to a gp160 trimer, the HIV surface densely glycosylated spike protein, which is responsible for mediating HIV-DC-SIGN interaction and viral infection. Thus, G5-DiMan may serve as a good mimic of gp160 for probing its interaction with DC-SIGN. The larger G13 and G27 were employed to investigate how GNP scaffold size impacts their MLGIs with DC-SIGN/R. The citrate stabilized G13 and G27 as prepared gave a single plasmonic absorption band at ~520 nm and ~522 nm, respectively, and displayed a single distribution species with a hydrodynamic diameter (Dh, volume population) of ∼16 and ∼29 nm for G13 and G27, respectively, consistent to that expected for isolated single G13 and G27 particles coated with a thin layer of citrate ligands (SI, Figs. and). Preparation of GNP-glycan conjugates. Gx-glycan conjugates (Gx capped with the corresponding LA-EG4-DiMan and/or LA-EG4-OH ligands) were prepared by incubation of citrate-stabilized GNPs overnight with the pure LA-EG4-DiMan or mixed LA-EG4-DiMan/LA-EG4-OH ligands (glycan ligand content varied from 100%, 75%, 50%, 25% to 0% to tune the GNP surface glycan ligand density) in water under a fixed total ligand: GNP molar ratio of 1000:1 for G5, 3000 for G13, or 10000 for G27.