title: Ultra-low-volume, real-time measurements of lactate from the single heart cell using microsystems technology.
abstract: The fabrication of microelectrodes integrated within ultra-low-volume microtiter chambers for the amperometric determination of metabolites continues to be of interest in the subject of single-cell and high-throughput screening. The microsystem described in this paper consists of a two-microelectrode sensor with a microfluidic dispensation technology, which is able to deliver both very low titers (6.5 pL) and single heart cells into a low-volume microphotoelectrochemical cell. Devices were fabricated using photolithography and liftoff giving reproducible sensors integrated within high aspect ratio titer chambers (with a volume of 360 pL), made of the photoepoxy SU8. In this paper, the determination of lactate was optimized using an enzyme-linked assay based upon lactate oxidase, involving the amperometric determination of hydrogen peroxide at +640 mV versus an internal Ag/AgCl pseudoreference. The microsystem (including the microfluidic dispensers and structures as well as the microsensor) was subsequently used to measure the lactate content of single heart cells. Dynamic electrochemical measurements of lactate during cell permeabilization are presented. We also show the use of respiratory uncouplers to simulate ischemia in the single myocyte and show that, as expected, the rate of lactate production from the hypoxic heart cell is greater than that within the normoxic healthy myocyte.
authors.affiliation: Bioelectronics Research Centre, Department of Electronics and Electrical Engineering, University of Glasgow, UK.
authors.forename: Xinxia
authors.initials: X
authors.lastname: Cai
authors.forename: Norbert
authors.initials: N
authors.lastname: Klauke
authors.forename: Andrew
authors.initials: A
authors.lastname: Glidle
authors.forename: Peter
authors.initials: P
authors.lastname: Cobbold
authors.forename: Godfrey L
authors.initials: GL
authors.lastname: Smith
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Cooper
mesh_terms: D007202:Indicators and Reagents; D019344:Lactic Acid / Q000032:analysis*; D008084:Lipoxygenase / Q000737:chemistry; D008670:Metals / Q000737:chemistry; D008839:Microelectrodes; D009206:Myocardium / Q000737:chemistry* / Q000166:cytology*; D036103:Nanotechnology
chemical_list: D007202:Indicators and Reagents; D008670:Metals; D019344:Lactic Acid; D008084:Lipoxygenase