Holographic Glucose Sensors - Holographic Sensors - page 119

Fig. 5.17 Bragg peak measurements of the holographic sensor for three independent (random)
urine samples of diabetic patients (pH 7.4). The increase in the slope shows an increase in the
concentration of the carbohydrate in the urine samples. The sensor was reset in * 10 s, and the
Bragg peak baseline was 519 ± 5.8 nm

concentrations of glucose in urine samples. The values were correlated to the
concentration of glucose found with Multistix ® 10 SG (GOx method, Siemens)
strips with CLINITEK Status ® + Analyzer and the fully-automated Dimension ®
Clinical Chemistry System (hexokinase-glucose-6-phosphate dehydrogenase
method (HK/G6P-DH), Siemens). Analyses with the urine strip tests were
performed by brie 1 s) dipping the Multistix ® 10 SG test strip into the urine

sample and ensuring that all test areas were moistened. While withdrawing the test
strip from the urine sample, the edge of the test strip was wiped against the rim of
the recipient to remove excess urine, followed by 1 s blot drying. After 60 s of
reaction time, the test strip was analysed with CLINITEK Status ® + Analyzer. As a
control, the reaction colours of the test strips were also compared to the reference
chart provided by the supplier. The sensitivity of HK/G6P-DH glucose assay was
0.056 mmol/L [ 55 ]. Hexokinase catalyses the phosphorylation of glucose in the
presence of adenosine-5

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*

-triphosphate (ATP) and Mg 2+ ions to form glucose-6-
phosphate (G-6-P) and adenosinediphosphate (ADP). G-6-P is then oxidised by
glucose-6-phosphate dehydrogenase (G-6-PDH) in the presence of nicotinamide
adenine dinucleotide (NAD + ) to produce 6-phosphogluconate and nicotinamide
adenine dinucleotide hydride (NADH). One mole of NAD + is reduced to one mole
of NADH for each mole of glucose present. The absorbance due to NADH (hence
glucose concentration) was determined using a bichromatic (340 and 383 nm)
endpoint technique. Reagents in HK/G6P-DH method included HK (15 U/mL,
liquid, yeast sourced, well 1), G-6-PDH (30 U/mL, yeast sourced, wells 2), NAD +
(8 mmol/L, well 3), ATP (15 mmol/L, well 4), Mg 2+ ions (7.4 mmol/L, well 5), and
stabiliser and buffer (well 6).

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