To perform the respective analysis on a sample, representative material must be transported to the biosensor. A fluidic system (tubing set) consisting of tubing lines, pumps and valves is used for that purpose. Additionally, the sample is also conditioned in the fluidic system, i.e. potentially interfering components are removed, and diluted to the extent that it can be assayed reliably by highly sensitive biosensors.
This is done by separation through a dialysis membrane, which is integrated in every tubing set as a diffusion module. Conditioning of the sample is based on the method of flow diffusion analysis (see figure). This method works with a time-dependent sample transfer. For that purpose, the measurement line and the sample and | or the sample infeed are separated from each other by a membrane. The measuring side is called the acceptor (receiving) and the sample side is called the donor (giving).
During an analysis, the measurement line is flushed with a transport buffer, which is an acceptor stream that can be stopped from behind the membrane for a defined period of time. This procedure is carried out by triggering a valve, which in turn opens up a bypass route. Meanwhile, the analytes in the sample diffuse through the membrane and, at the same time, are enriched in the holding chamber. In this way, a continually increasing concentration of dialysable components develops in the fluid segment of the transport buffer.
When this segment is released by re-triggering the valve, the flow goes to the measurement cell where it generates a signal. The intensity of the signal is a measure of the concentration of the sample. One big advantage of this enrichment method is the very broad measuring range that is achieved by varying the diffusion time; it also protects the sensor against inferring particles in the sample.
Application specific tubing sets
With the aid of pre-assembled tubing sets and associated transport and calibration solutions fully automatic sampling and measurement can be performed using TRACE C2 Control / MultiTRACE.
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