Microfluidic device to confine single cardiac myocytes in sub-nanoliter volumes for extracellular pH measurements

We have combined a microfluidic network and miniature thin film pH sensors (40 x 40 m(2)) to trap and measure the acidification rates of single cardiomyocytes in a confined extracellular space. The miniature pH sensors were fabricated by electrodeposition of iridium oxide (IrOx) films on planar platinum microelectrodes. The pH electrodes as well as stimulation electrodes were integrated into the device with a 160 picoliter cell trap. Single cardiac cells were trapped in the sensing volume using pressure gradients. Miniature mechanical valves allowed the control of the fluidic flow in the network precisely to eliminate small residual flows. The measurement acidification rate of quiescent cells depended on the Ca2+ concentration of the media and was 6.45 +/- 0.4 mpH\min for 0.8 mM Ca2+ (n = 8) and 11.96 1.3 mpH\min for 1.8 mM Ca2+ (n = 9). Multiple cell traps equipped with pH sensors can be arranged on one chip. Such chips could have potential applications in high-content high throughput drug screening efforts.