pH-Sensitive Oscillatory Motion of a Urease Motor on the Urea Aqueous Phase

Area of Science:

• Biochemistry
• Chemical Engineering
• Materials Science

Background:

• Enzyme-driven self-propulsion is a growing field.
• Urease enzyme catalyzes urea hydrolysis, producing ammonia and carbon dioxide.
• Surface tension gradients can generate motion in micro-objects.

Purpose of the Study:

• Investigate self-propelled motion of a urease motor at the air/aqueous interface.
• Determine the effect of initial pH on motor motion and dynamics.
• Elucidate the mechanisms driving oscillatory and non-oscillatory motion.

Main Methods:

• Fabrication of a urease motor using immobilized urease on filter paper.
• Observation of motor behavior on aqueous urea solutions with varying initial pH.
• Analysis of motion dynamics, including frequency and speed.
• Correlation of motion with urease enzyme activity and surface tension gradients.

Main Results:

• The urease motor demonstrated pH-dependent self-propelled motion.
• Oscillatory motion was observed, with frequency and speed varying with initial pH.
• No motion was observed at certain pH values.
• The observed behaviors were linked to the bell-shaped pH-activity profile of urease and surface tension effects.

Conclusions:

• The pH of the urea solution critically influences the self-propulsion of urease motors.
• Urease enzyme's pH-dependent activity and resulting surface tension gradients are key to motion control.
• This study provides insights into enzyme-powered micro-machines and their environmental responsiveness.