Electrochemical detection of catecholamine exocytosis using planar iridium oxide electrodes in nanoliter microfluidic cell culture volumes

• Published in: Biosensors & bioelectronics 2011-12, Vol.34 (1), p.30-36
• Main Authors: Ges, Igor A., Currie, Kevin P.M., Baudenbacher, Franz
• Format: Article
• Language: English
• ISSN: 0956-5663; 1873-4235
• DOI: 10.1016/j.bios.2011.11.050

Release of neurotransmitters and hormones by Ca 2+ regulated exocytosis is a fundamental cellular/molecular process that is disrupted in a variety of psychiatric, neurological, and endocrine disorders. Therefore, this area represents a relevant target for drug and therapeutic development, efforts that will be aided by novel analytical tools and devices that provide mechanistically rich data with increased throughput. Toward this goal, we have electrochemically deposited iridium oxide (IrOx) films onto planar thin film platinum electrodes (20×300µm 2 ) and utilized these for quantitative detection of catecholamine exocytosis from adrenal chromaffin cells trapped in a microfluidic network. The IrOx electrodes show a linear response to norepinephrine in the range of 0–400µM, with a sensitivity of 23.1±0.5mA/(M·mm 2 ). The sensitivity of the IrOx electrodes does not change in the presence of ascorbic acid, a substance commonly found in biological samples. A replica molded polydimethylsiloxane (PDMS) microfluidic device with nanoliter sensing volumes was aligned and sealed to a glass substrate with the sensing electrodes. Small populations of chromaffin cells were trapped in the microfluidic sensing chamber and stimulated by rapid perfusion with high potassium (50mM) containing Tyrode’s solution at a flow rate of 1nL/s. Stimulation of the cells produced a rapid increase in current due to oxidation of the released catecholamines, with an estimated maximum concentration in the microfluidic device ~52µM. Thus, we demonstrate the utility of an integrated microfluidic network with IrOx electrodes for real-time quantitative detection of catecholamines released from small populations of cells.