Integrated electrochemical sensor array for on-line monitoring of yeast fermentations.

This paper describes the design, modeling, and experimental characterization of an electrochemical sensor array for on-line monitoring of fermentor conditions in both miniaturized cell assays and in industrial scale fermentations. The viable biomass concentration is determined from impedance spectroscopy. As a miniaturized electrode configuration with high cell constant is applied, the spectral conductivity variation is monitored instead of the permittivity variation. The dissolved oxygen concentration is monitored amperometrically using an ultramicroelectrode array, which is shown to have negligible flow dependence. pH is monitored using an ion-sensitive field effect transistor (ISFET), and a platinum thermistor is included for temperature measurements. All sensors were shown to be sufficiently accurate within the range relevant to yeast fermentations. The sensor array is shown to be very stable and durable and withstands steam-sterilization.

Monitoring enzymatic reactions in nanolitre wells.

We have developed a laboratory-on-a-chip microarray system based on nanolitre-capacity wells etched in silicon. We have devised methods for dispensing reagents as well as samples, for preventing evaporation, for embedding electronics in each well to measure fluid volume per well in real-time, and for monitoring the fluorescence associated with the production or consumption of NADH in enzyme-catalysed reactions. Such reactions can be found in the glycolytic pathway of yeast. We describe the design, construction and testing of our laboratory-on-a-chip. We also describe the use of these chips to measure both fluorescence (such as that evidenced in NADH) as well as bioluminescence (such as evidenced in ATP assays). We show that our detection limit for NADH fluorescence is 5 micro m with a microscope-based system and 100 micro m for an embedded photodiode system. The photodiode system also provides a detection limit of 2.4 micro m for ATP/luciferase bioluminescence.

The inhibition of blood coagulation by heparins of different molecular weight is caused by a common functional motif--the C-domain.

BACKGROUND: Heparins in clinical use differ considerably as to mode of preparation, molecular weight distribution and pharmacodynamic properties. OBJECTIVES: Find a common basis for their anticoagulant action. METHODS: In 50 fractions of virtually single molecular weight (Mr), prepared from unfractionated heparin (UFH) and four low-molecular-weight heparins (LMWH), we determined: (i) the molar concentration of material (HAM) containing the antithrombin binding pentasaccharide (A-domain); (ii) the specific catalytic activity in thrombin and factor Xa inactivation; (iii) the capacity to inhibit thrombin generation (TG) and prolong the activated partial thromboplastin time (APTT). We also calculated the molar concentration of A-domain with 12 sugar units at its non-reducing end, i.e. the structure that carries antithrombin activity (C-domain). RESULTS: The antithrombin activity and the effects on TG and APTT are primarily determined by the concentration of C-domain and independent of the source material (UFH or LMWH) or Mr. High Mr fractions (>15 000) are less active, probably through interaction with non-antithrombin plasma proteins. Anti-factor Xa activity is proportional to the concentration of A-domain, it is Ca2+- and Mr-dependent and does not determine the effect on TG and APTT. CONCLUSION: For any type of heparin, the capacity to inhibit the coagulation process in plasma is primarily determined by the concentration of C-domain, i.e. the AT-binding pentasaccharide with 12 or more sugar units at its non-reducing end.