Both DC-SIGN and DC-SIGN-C showed very similar association FRET ratio-time profiles for 𝑥 0 = 20 nM, which gave maximal FRET ratios similar to those obtained in Fig. within 10 s, indicating that optimal binding was achieved (Fig. ). The second order rate equation fitted nicely for DC-SIGN and DC-SIGN-C, yielding 𝑘 𝑜𝑛 values of (2.24 ± 0.06) ×10 7 M -1 s -1 and (2.92 ± 0.04) ×10 7 M -1 s -1 and half-lives (𝑡 ½ ) of 1.55 ± 0.04 s and 1.19 ± 0.02 s, respectively (where, 𝑡 ½ = ln(2) /(𝑥 0 𝑘 𝑜𝑛 ); Table ). DC-SIGN-C association is slightly faster, consistent with its slightly stronger affinity with QD-DiMan, found in the thermodynamic studies (Table ). A much lower FRET ratio was observed for DC-SIGNR due to its low binding affinity at a 1:1 PQR, which was used in order to obtain relevant rate coefficients for all three proteins. This resulted in relatively poor fits due to the low signal to noise ratio. This was only slightly improved by taking an average of every 5 measurements, resulting in a time resolution of 0.0625 s. However, despite this, significant trends can still be observed. It was found that, despite a relatively rapid initial association, DC-SIGNR was not able to reach saturation, even after 60 s, resulting in a negative 𝑎-term. Here, though the positive 𝑎-terms observed for DC-SIGN and DC-SIGN-C may account for the gradual decay in QD and/or dye fluorescence with time, the negative term DC-SIGNR cannot be related to the individual QD or dye fluorescence, it must be a result of another form of association between the two species which occurs over a much longer timespan.