Development of a novel reagentless, screen-printed amperometric biosensor based on glutamate dehydrogenase and NAD+, integrated with multi-walled carbon nanotubes for the determination of glutamate in food and clinical applications

© 2015 Elsevier B.V. Abstract A screen printed carbon electrode (SPCE) containing the electrocatalyst Meldola's Blue (MB) has been investigated as the base transducer for a reagentless glutamate biosensor. The biopolymer chitosan (CHIT) and multiwalled carbon nanotubes (MWCNTs) were used to encapsulate the enzyme glutamate dehydrogenase (GLDH) and the co-factor nicotinamide adenine dinucleotide (NAD+). The biosensor was fabricated by sequentially depositing the components on the surface of the transducer (MB-SPCE) in a layer-by-layer process, details of which are included in the paper. Each layer was optimised to construct the reagentless device. The biosensor was used in conjunction with amperometry in stirred solution using an applied potential of +0.1 V (vs. Ag/AgCl). Optimum conditions for the analysis of glutamate were found to be: temperature, 35°C; phosphate buffer, pH 7 (0.75 mM, containing 0.05 M NaCl). The linear range of the reagentless biosensor was found to be 7.5-105 μM, and limit of detection was found to be 3 μM (based on n = 5, CV: 8.5% based on three times signal to noise) and the sensitivity was 0.39 nA/μM (±0.025, coefficient of variation (CV) of 6.37%, n = 5). The response time of the biosensor was 20-30 s. A food sample was analysed for monosodium glutamate (MSG). The endogenous content of MSG was 90.56 mg/g with a CV of 7.52%. The reagentless biosensor was also used to measure glutamate in serum. The endogenous concentration of glutamate was found to be 1.44 mM (n = 5), CV: 8.54%. The recovery of glutamate in fortified serum was 104% (n = 5), CV of 2.91%

USING DRIED URINE SAMPLES FOR BIOMARKER MEASUREMENTS

We tested 181 dried urine samples spotted on regular cosmetic cotton swabs for quantitative analysis of various potentially alcoholic beverage related metabolites across wide polarity and structural ranges. The samples were collected in a 3-week cross-over intervention trial with alcoholic beverages and abstention. The agreement of measurements between conventional 24-hour urines and dried urine spots made from them in situ corrected with creatinine ratio was evaluated by Passing-Bablok regression and Bland-Altman analysis. Determinations were performed by a recently developed and fully validated UPLC-MSMS multiplex method. There was full agreement in qualitative results making dried urine spots suitable for metabolomics profiling and screening analysis useful for compliance control in clinical trials. Quantitative analysis exposed certain limitations of dried spotting. Based on the slopes calculated from Passing-Bablok regression, results were underestimated in the range of 11-23% in case of tartaric acid, indoxyl sulfate, pyroglutamyl proline and dihydroepiandrosterone sulphate. Agreement was found in case of the alcohol intake related metabolites, ethyl sulfate and ethyl glucuronide. Partial overestimation ranging from 10-20% was observed for cresol sulfate. As a secondary objective, we examined variance of individual total daily creatinine excretion which was found to be up to 16%, comparing seven 24-hour urine samples collected from each of the 26 subjects. This finding suggests that a creatinine correction factor could be calculated as an average individual value obtained from several 24 hour urine samples. A creatinine correction factor could be useful in some long-term clinical trials for correction of measurements in dried urine spots provided that the resulting analytical error is acceptable for the research purpose

Amperometric Lactate Biosensor Based on Carbon Paste Electrode Modified with Benzo[ c

Amperometric lactate biosensor based on a carbon paste electrode modified with benzo[c]cinnoline and multiwalled carbon nanotubes is reported. Incorporation of benzo[c] cinnoline acting as a mediator and multiwalled carbon nanotubes providing a conduction pathway to accelerate electron transfer due to their excellent conductivity into carbon paste matrix resulted in a high performance lactate biosensor. The resulting biosensor exhibited a fast response, high selectivity, good repeatability and storage stability. Under the optimal conditions, the enzyme electrode showed the detection limit of 7.0 x 10(-8) M with a linear range of 2.0 x 10(-7) M-1.1 x 10(-4) M. The usefulness of the biosensor was demonstrated in serum samples.Namik Kemal University Research FundNamik Kemal University [NKUBAP.00.10.YL.12.04]; Ankara University Research FundAnkara University [14L0430005]We gratefully acknowledge the financial support of Namik Kemal University Research Fund (Project No: NKUBAP.00.10.YL.12.04) and Ankara University Research Fund (Project No: 14L0430005)