Micromachined Amperometric Cells for Continuous Monitoring of Glucose and Lactate

Abstract

Design, set-up and test of miniaturized amperometric cells are described. These sensors are produced using silicon micromachining technologies to minimise geometrical sensor dimensions and chemical conversion rate for measurements in small sample volumes. The sensors use conventional reactions of glucose- or lactate-oxidase with amperometric detection of H2O2. A novel sensor design is described with external dimensions of 3,0 mmtimes6,0 mmtimes0,7 mm that includes a working-, counter- and an iridium reference electrode. This chip contains a cavity filled with immobilised glucose- or lactate-oxidase. The reaction chamber exchanges material with the analyte by diffusion through a thin (12mum) silicon membrane with an array of well-defined holes etched through the silicon membrane. Number and size of the pores can be varied to adjust the sensor to the required sensitivity and linear measuring range. These sensors have been developed and adjusted for continuous and reliable supervision of mobile persons. All sensors were tested and characterised in vitro prior to using them for measurements in saliva and interstitial fluid. For glucose sensors the linear range was designed between 0,5 and 20 mM glucose concentration. The glucose sensors were tested in interstitial fluid and used in clinical trials for continuous glucose measurement in patients. Linear range of lactate sensors was adjusted from 0,1 to 5 mM. Tests for lactate sensors were performed using saliva of persons under exercise. Sensor readings of both sensor types were compared to blood concentrations of glucose or lactate determined using standard laboratory equipment