Fig. 1.
Antichemotaxis of urease when it catalyzes urea hydrolysis in a microfluidic channel. (A) Design scheme of the microfluidic chip. The enzyme–substrate–buffer (E+S+B) enters one inlet, and the substrate-free enzyme solution in buffer (E+B) enters another, producing constant enzyme concentration across the channel but a linear gradient of its substrate. (B) Urease concentration extracted from FCS autocorrelation fitting to Eq. 1 (solid circles) and calibrated urea concentration (open circles) are plotted against position across channel with error bars showing SD of five repeated measurements. Dotted line through the data is the hyperbolic profile predicted by the model. (C) The enzyme diffusion coefficient (Da) extracted from FCS autocorrelation fitting with a diffraction-limited spot size, plotted against position in the channel, in the presence (solid squares) and absence (open squares) of substrate.