GNP is well-known for its strong fluorescence quenching properties via a nanoscale surface energy transfer mechanism (NSET, QE ∝ 1/R , where QE and R are the quenching efficiency and dye-GNP distance, respectively), which is more effective and covers a longer distance range than the Förster resonance energy transfer (QE ∝ 1/R 6 ). Therefore, binding of G13-CRD with DiMan-QD will bring the QD and GNP into close proximity, resulting in efficient quenching of QD fluorescence. The QE here represents the percentage of added QDs that have bound to G13-CRD (SI, Section 5.3.3). As expected, the fluorescence of QD-DiMan (2 nM) was quenched efficiently (>80%) upon mixing with G13-Tz-CRD100 (1 nM, Fig. ). In contrast, QD-Gal was quenched much less efficiently (~10%, Fig. ), and a non-glycosylated QD-EG4-OH control (a DHLA-EG4-OH ligand capped QD) showed no apparent quenching under such conditions. Fitting the QE-concentration relationship for 1:1 mixed G13-Tz-CRD100 and QD-DiMan sample by Hill's equation yielded an apparent binding equilibrium dissociation constant, Kd, of 0.93±0.05 nM (Fig. ). This represents an impressive ~1 million-fold enhancement of affinity over that of monovalent CRD-DiMan binding (Kd = 0.9 mM). A similar sub-nM Kd was also obtained for G13-CRD100 binding with QD-DiMan (SI, Fig. ). These results confirm that G13-CRDs have not only retained CRD's native binding specificity with DiMan but also drastically enhanced its affinity via forming multivalent binding (Fig. ). Free tetrameric ECD (before GNP-conjugation) was shown to bind strongly with QD-DiMan with low to sub nM Kd. However, G13-Tz-ECD100 only gave a QE about ~ ¼ of that obtained with G13-Tz-CRD100 after mixing with QD-DiMan (Fig. ). The ineffective quenching here is attributed to long rigid coiled-coil neck (>20 nm) in ECD which project CRDs away from GNP surface, resulting in a large GNP-QD separation distance and hence ineffective quenching after binding.