Quartz Nanopore Membranes for Low Noise Measurements of Ion Channel Conductance

Planar lipid bilayer (PLB) apparatus provide an excellent platform for the study of isolated membrane proteins. The noise performance and bandwidth of PLB systems are poor relative to the state of the art in patch clamp/pipette apparatus. The problem is the relatively high capacitance of PLB systems relative to small area patch pipettes. At low frequencies (hundreds of Hz), the difference is small to non-existent. At higher frequencies, the noise becomes dominated by voltage noise from the amplifier acting on capacitance of the lipid bilayer and surrounding platform. With a much larger area, the noise for the PLB system rapidly exceeds that of the patch pipette. At intermediate frequencies (1 to 10's of kHz), the specific composition of the PLB platform can lead to an increase in noise due to dielectric loss [1].We have developed a PLB system based upon a quartz nanopore membrane (QNM) with noise performance approaching the state of the art for patch clamp systems. Due to low dielectric loss, the QNM represents a significant advance in performance over the previously presented glass nanopore membrane [2] and provides for noise performance of ∼200 fA at a 10 kHz bandwidth when coupled to a simple capacitive feedback amplifier. The resulting system has great immunity to vibration and electrical interference, without the need for a vibration isolation table and a large faraday shield. This new PLB platform will open up the potential for making very high bandwidth single channel measurements that were not previously possible.[1] R. A. Levis, et al, Methods in Enzymology, 293, pp. 218-266, 1998[2] R. J. White, et al, J. Am. Chem. Soc., 129, pp. 11766-11775, 2007