We report herein an efficient method to control pH in reactions catalyzed by hydrolytic enzymes, such as the degradation of paraoxon by phosphotriesterase (E.G. 3.1.8.1; OPH), using urease-catalyzed (E.G. 3.5.1.5) urea hydrolysis as a buffering agent. Given the distinct pH profiles of urease and OPH activities, urease produces base on demand in response to pH drop during paraoxon detoxification. As pH changes, the enzyme activities fluctuate to finally stabilize at a pH "set-point," where the rates of acid and base generation are equal. By varying the urease to OPH ratio, various pH "set-points" ranging between 6.5 and 8.5 were achieved within minutes and could be predicted theoretically. This dynamic approach for pH control was successfully applied to the development of a positive-response inhibition-based sensor.