An iridium oxide microelectrode for monitoring acute local pH changes of endothelial cells

Abstract

pH sensors were fabricated by anodically electrodepositing iridium oxide films (AEIROFs) onto microelectrodes on chips and coated with poly(ethyleneimine) (PEI) for mechanical stability. These demonstrate super-Nernstian response to pH from pH 4.0 to 7.7 in chloride-free phosphate buffer. The surface of the chip was coated with fibronectin for the attachment of porcine aortic endothelial cells (PAECs). The working capability of the pH sensor for monitoring acute local pH changes was investigated by stimulating the PAECs with thrombin. Our results show that thrombin induced acute extracellular acidification of PAECs and dissolution of fibronectin, causing the local pH to decrease. The use of PD98059, a mitogen-activated protein kinase (MAPK) inhibitor, reduced extracellular acidification and an increase in local pH was observed. This study shows that our pH sensors can facilitate the investigation of acute cellular responses to stimulation by monitoring the real-time, local pH changes of cells attached to the sensors.

Micropatterning of planar metal electrodes by vacuum filling microfluidic channel geometries

“…Under certain electrical conditions necessary for the lysis of cells, we witness deterioration and lift off of portions of the electrodes from the glass substrate. Polyethylenimine (PEI) is commonly used to increase the adhesion of electrode materials 43 . PEI spun coat onto electrodes was able to prevent lift-off and is used for all subsequent experiments.…”

Development of a Minimally Invasive Microneedle-Based Sensor for Continuous Monitoring of β-Lactam Antibiotic Concentrations in Vivo

“…It has, however, been shown to provide mechanical stability. 40 The limit of detection for the optimised composition is 6.8±1.04 µM (n=3) in 10 mM PBS solution. In reality, although the buffer capacity of interstitial fluid is not known, it is likely to be considerably lower than that of 10 mM PBS (a conservative estimate chosen for testing).…”

“…39 Iridium oxide offers an alternative to a glass pH electrode and was chosen due to its improved stability, fast response time and low impedence. 40 Optimisation of the biosensor is shown along with proof-of-concept in vivo data from a healthy volunteer to demonstrate the potential of this technology.…”

An array of individually addressable micro-needles for mapping pH distributions

“…[18][19][20][21] In addition, an array of pH sensors provide a better mapping of tissues or organs than a single-spot device because of possible heterogeneities across different sites and along the depth of the sample. 22,23 In this regard, it is important to note that the fabrication of an array from glass-type pH electrodes is a difficult process.…”

“…24,2 5 Iridium oxide electrodes exhibit a super-Nernstian response of 65-80 mV/pH unit depending on preparation and discussions over the complex equilibrium interfacial reactions that account for this behaviour can be found elsewhere. 18,[24][25][26] An example of heterogeneous pH variation is the setting of myocardial ischemia due to a switch towards anaerobic metabolism and the development of lactic acidosis. [27][28][29][30][31][32] Reperfusion of ischemic myocardium 33 leads to a rapid restoration of pH to pre-ischemic values, 34,35 which may in part contribute towards reperfusion injury.…”