Description of Instrumentation and Procedures - Advances in Biochemical Engineering Biotechnology - page 19

Fig. 9. The linear range for urea detection using a miniaturized thermometric system

preservative was also included in the tubes. For lactate, this preservative does
not stabilize the concentration and may inhibit enzyme activity [21, 30]. Urea
(Fig. 9) was relatively stable for several hours after withdrawal. Using the
thermal biosensors, the blood samples were directly analyzed without any addi-
tional treatment. The sampling rate in this case was from 12 to 90 assays per
hour. Meanwhile, the same samples were determined with the reference
methods. In the UV reference method, it is necessary to deproteinize the blood
in order to stop the metabolism of several unstable analytes, since this method
takes much longer than the biosensor method. This was achieved by adding per-
chloric acid to the blood at the start of the thermometric determination,in order
to reduce the measurement error due to the concentration change in the sample.
Higher concentrations of blood metabolites for comparison were achieved by
adding small volumes of high concentration standards into the native blood
samples. The results of the determination of glucose, urea and lactate [31] in
whole blood are summarized in Table 2.

Table 2. Determination of glucose, urea, and lactate in undiluted blood using miniaturized
thermal sensors

Metabolite Linear range CV (%) Sample Correlation Reference

(mM) volume ( m l) coefficient method

Glucose 0.5-20 3.7 a 1 0.980 c Reflolux-S

Urea 0.2-50 4.1 b 1 0.989 d UV

Lactate 0.2-14 1 0.984 d UV

a For 100 samples, b For 50 samples, c For 37 samples, d For 30 samples.