Chemoelectrical Energy Conversion of Adenosine Triphosphate using ATPases

Abstract

Biological ion transport processes in proteins have inspired the development of bio-sensors, actuators, photoelectric, and chemoelectric energy conversion devices. These bio-inspired devices use ion transport through a protein energized by biochemical reactions in the protein’s sub-units to perform their engineering function. In an effort to advance the use of biological processes in synthetic systems, a chemoelectrical energy conversion device is demonstrated in this article that uses hydrolysis of adenosine triphosphate (ATP) in ATPase enzyme to generate electrical power. The ATPase enzyme in the device is reconstituted in a bilayer lipid membrane (BLM) and supported on a porous substrate. ATP is dissolved in pH7 buffer and added to one of the chambers in this bicameral device. The transmembrane gradient established by proton transport, resulting from hydrolysis of ATP in the enzyme, is converted into electron flow in an external circuit via silver-silver chloride electrodes placed in the buffer solution on both the sides of the membrane. The chemoelectrical energy conversion of ATP is demonstrated in this article using electrical impedance spectroscopy and load characterization experiments on BLMs supported in the pore(s) of a 25% porous polycarbonate membrane and single-pore silicon nitride chip. In electrical impedance spectroscopy, the change in conductance states of the membrane quantified by specific resistance is used to demonstrate protein activity. The mean electrical impedance of the BLM with ATPase supported on a single pore silicon nitride chip drops from 7 kΩ cm2 to 250 Ω cm2 on adding ATP to one side of the membrane. This change in ionic conductance of the BLM with ATPase in the presence of ATP demonstrates protein activity in the membrane. Impedance analysis of the membranes (BLM, BLM with ATPase) supported in multi-pore polycarbonate substrate demonstrates similar trend confirming ion transport and energy conversion in the membrane. In load characterization experiments, a resistive load of known magnitude is connected to the device and voltage across the membrane and current through the circuit are measured. The current−voltage characteristics of the device resembles a constant current power source and the slope of the response represents the internal resistance of the device. The current through the membrane supported on the single pore substrate is below the range of our data acquisition equipment and hence the device with the porous polycarbonate membrane is used in load characterization experiments. This polycarbonate membrane-based device has an open-circuit voltage of 87.5(±7.5) mV with a specific power output of 1.85 μW/cm2 and an internal resistance of 30.5k(±8.5k)Ω. The theoretical maximum specific power available from the membrane supported on the multi-pore polycarbonate membrane and the single pore silicon-nitride substrate are estimated from the current−voltage response to be 7.65 and 18 μW/cm2.