The open container-used microfluidic chip using IrOx ultramicroelectrodes for the in situ measurement of extracellular acidification

The measurement of metabolic activity based on the extracellular acidification rate has attracted wide interests in the field of biochemical detection. In the study, the chip comprising a microfluid-controlled open container and iridium oxide (IrOx) pH ultramicroelectrodes (UMEs) was constructed for the purpose of in situ measurement of extracellular acidification rate. The feasible anodic depositing parameters of IrOx film were in the range of +0.53 to +0.8 V by means of exploring the electrochemical properties of alkaline Ir(IV) deposition solution. The IrOx pH UMEs electrodeposited for 300 cycles between 0 V and +0.6 V exhibited the near-super-Nernstian sensitivity of −68 to −76 mV/pH and the good stability with potential drifting of 11.7 mV within 24 h. The design of the open container connected with a position-raised microchannel improved the sensing stability of IrOx pH UMEs, with the potential deviation of as low as 0.1 mV under the flow rate of 20 μl/min. The acidification rate of HeLa cells (2160 cells/mm2) repeatedly measured 5 times in the microfluidic chip showed the good reproducibility of 0.021 ± 0.002 pH/min. Moreover, the chip can decrease the acidosis occurrence, a decrease of only 0.13–0.17 pH unit in 8 min interval, during the measurement of cellular metabolic activity.