The fluorescence spectra of the lectins (varying concentrations) without and with a fixed concentration of Gx-glycans were recorded under an excitation wavelength, λex, of 630 nm, where Gxs have minimal absorption, to reduce any possible interference. All binding studies were carried out in a binding buffer containing 1 mg/mL of bovine serum albumin (BSA) as described earlier, to make the binding conditions more closely resemble real biological situations. Moreover, this also greatly reduced any non-specific interactions and adsorption of proteins and GNPs to surfaces, which can be a major source of experiments errors at low concentrations, e.g. < 10 nM. The fluorescence spectra showing the binding between DC-SIGN/R and Gx-DiMan were given in SI, Figs. S12-S17. In the absence of Gx-DiMan, DC-SIGN/R's fluorescence increased linearly with concentration, but their fluorescence was greatly reduced in the presence of Gx-DiMan, consistent with binding-induced fluorescence quenching by the GNPs in proximity. Moreover, free mannose effectively competed with Gx-DiMan binding with DC-SIGN/R, giving rise to a significant, dose-dependent recovery of DC-SIGN/R fluorescence (SI, Figs. S19-20). Further, mixing DC-SIGN/R with the control Gx-OH produced negligible quenching, confirming that the fluorescence quenching observed with Gx-DiMan was due to specific MLGIs between Gx-DiMan and DC-SIGN/R (SI, Fig.