Figure 4.

(a) Single-MSPRS signal (at 660 nm) during surface-bound GOx (Figure 2a) interaction with L-Glu, 2Do-Glu, D-Man and D-Glu solutions (all substrates dissolved at 100 mM in PBS). Flow rate 0.5 nL/s. Solution temperature 24.0 ± 0.1 °C. The L-Glu signal serves as a control for the effect of the refractive indices of the substrate solutions vs PBS because it does not bind to GOx. D-Glu produces a fast signal change due to the refractive index of the solution followed by a slower change due to formation of the βD-Glu–GOx complex. D-Glu 100 mM in PBS (50 mM βD-Glu equivalent) interacts with GOx. D-Man and 2Do-Glu interact very weakly with GOx. This experiment used the same MSPRS as in Figure 2a,b. (b) Biacore 3000 signals during an equivalent experiment. Flow rate 10 μL/s. Solution Temperature 25°C. We have subtracted the reference-channel signal from the functionalized-channel signal (Figure 2c). The uniform 25 ± 3 RU signal change for all substrates indicates sensitivity to the solutions’ refractive indices, but no detection of βD-Glu–GOx binding.