Yongjin Chung

Highly sensitive glucose biosensor using new glucose oxidase based biocatalyst

Glucose, which is a primary energy source of living organisms, can induce diabetes or hypoglycemia if its concentration in blood is irregular. It is therefore important to develop glucose biosensor that reads the concentration of glucose in blood precisely. In the present work, we suggest new glucose oxidase (GOx) based catalysts that can improve the sensitivity of the glucose biosensor and make glucose measurements over a wide concentration ranges possible. For synthesizing such catalysts, a composite including pyrenecarboxaldehyde (PCA) and GOx is attached to substrate including carbon nanotube (CNT) and polyethyleneimine (PEI) (CNT/PEI/[PCA/GOx]). Catalytic activity and stability of the catalyst are then evaluated. According to the investigation, the catalyst shows excellent glucose sensitivity of 47.83 μAcm−2mM−1, low Michaelis-Menten constant of 2.2 mM, and wide glucose concentration detection, while it has good glucose selectivity against inhibitors, such as uric acid and ascorbic acid. Also, its activity is maintained to 95.7% of its initial value even after four weeks, confirming the catalyst is stable enough. The excellence of the catalyst is attributed to hydrophobic interaction, C=N bonds, and π-hydrogen interaction among GOx, PCA and PEI/CNT. The bindings play a role in facilitating electron transport between GOx and electrode.

A correlation of results measured by cyclic voltammogram and impedance spectroscopy in glucose oxidase based biocatalysts

A new biocatalyst consisting of glucose oxidase (GOx) and polyethylenimine (PEI) immobilized on carbon nanotube (CNT) (CNT/PEI/GOx) was developed, while cyclic voltammogram (CV) behaviors of several related catalysts including the CNT/PEI/GOx were analyzed in terms of charge transfer resistances (Rcts) obtained by measuring Nyquist plots using electrochemical impedance spectroscopy (EIS). A qualitative correlation between the flavin adenine dinucleotide (FAD) redox reactivity measured by the CV and Rct was established. As factors affecting both the FAD reactivity and Rct, concentrations of GOx, glucose, and phosphate buffer solution, electrolyte pH and ambient condition were considered and evaluations of the catalysts using the CV curves and Nyquist plots confirmed that a pattern in the FAD reactivity was closely linked to that in the Rct, implying that FAD reactivities of the catalysts are predicted by the measurements of their Rcts. Even regarding performance of the enzymatic biofeul cells (EBCs) using the reacted catalysts, a pattern of the Rcts is compatible with that in the maximum power densities (MPDs) of the EBCs.

Performance Improvement of Glucose Sensor Adopting Enzymatic Catalyst bonded by Glutaraldehyde

>> In this study, we synthesized a biocatalyst consisting of glucose oxidase (GOx), polyethyleneimine (PEI) and carbon nanotube (CNT) with addition of glutaraldehyde (GA)(GA/[GOx/PEI/CNT])for fabrication of glucose sensor. Main bonding of the GA/[GOx/PEI/CNT] catalyst was formed by crosslinking of functional end groups between GOx/PEI and GA. Catalytic activity of GA/[GOx/PEI/CNT] was quantified by UV-Vis and electrochemical measurements. As a result of that, high immobilization ratio of 199% than other catalyst (with only physical adsorption) and large sensitivity value of 13.4 μA/cm 2 /mM was gained. With estimation of the biosensor stability, it was found that the GA/[GOx/PEI/CNT] kept about 88% of its initial activity even after three weeks. It shows GA minimized the loss of GOx and improved sensing ability and stability compared with that using other biocatalysts.

A Study on Glucose Sensing Measured by Catalyst Containing Multiple Layers of Glucose Oxidase and Gold Nano Rod

In this study, we propose a catalyst structure including enzyme and metal nano rod for glucose sensing. In the catalyst structure, glucose oxidase (GOx) and gold nano rod (GNR) are alternatingly immobilized on the surface of carbon nanotube (CNT), while poly(ethyleneimine) (PEI) is inserted in between the GOx and GNR to fortify their bonding and give them opposite polarization ((GOx/GNR)nPEI/CNT). To investigate the impact of (GOx/GNR)nPEI/CNT on glucose sensing, some electrochemical measurements are carried out. Initially, their optimal layer is determined by using cyclic voltammogram and as a result of that, it is proved that (GOx/GNR/ PEI)2/CNT is the best layer. Its glucose sensitivity is 13.315 μAmM -1 cm -2 . When it comes to the redox reaction mechanism of flavin adenine dinucleotide (FAD) within (GOx/GNR/PEI)2/CNT, (i) oxygen plays a mediator role in moving electrons and protons generated by glucose oxidation reaction to those for the reduction reaction of FAD and (ii) glucose does not affect the redox reaction of FAD. It is also recognized that the (GOx/GNR/PEI)3/CNT is limited to the surface reaction and the reaction is quasi-reversible.