A New Route to the Considerable Enhancement of Glucose Oxidase (GOx) Activity: The Simple Assembly of a Complex from CdTe Quantum Dots and GOx, and Its Glucose Sensing

Abstract

A new complex consisting of CdTe quantum dots (QDs) and glucose oxidase (GOx) has been facilely assembled to achieve considerably enhanced enzymatic activity and a wide active temperature range of GOx; these characteristics are attributed to the conformational changes of GOx during assembly. The obtained complex can be simultaneously used as a nanosensor for the detection of glucose with high sensitivity. A mechanism is put forward based on the fluorescence quenching of CdTe QDs, which is caused by the hydrogen peroxide (H2O2) that is produced from the GOx-catalyzed oxidation of glucose. When H2O2 gets to the surface of the CdTe QDs, the electron-transfer reaction happens immediately and H2O2 is reduced to O2, which lies in electron hole traps on CdTe QDs and can be used as a good acceptor, thus forming the nonfluorescent CdTe QDs anion. The produced O2 can further participate in the catalyzed reaction of GOx, forming a cyclic electron-transfer mechanism of glucose oxidation, which is favorable for the whole reaction system. The value of the Michaelis-Menton constant of GOx is estimated to be 0.45 mM L(-1), which shows the considerably enhanced enzymatic activity measured by far. In addition, the GOx enzyme conjugated on the CdTe QDs possesses better thermal stability at 20-80 degrees C and keeps the maximum activity in the wide range of 40-50 degrees C. Moreover, the simply assembled complex as a nanosensor can sensitively determine glucose in the wide concentration range from micro- to millimolar with the detection limit of 0.10 microM, which could be used for the direct detection of low levels of glucose in biological systems. Therefore, the established method could provide an approach for the assembly of CdTe QDs with other redox enzymes, to realize enhanced enzymatic activity, and to further the design of novel nanosensors applied in biological systems in the future.

Fluorescent nanoparticles for chemical and biological sensing

“…NAD-dependent glucose dehydrogenase and CdSe/ZnS QDs or AuNPs were integrated for optical detection of glucose [152]. Meanwhile, glucose was also monitored by analyzing the quenching of QDs by the enzyme-generated H 2 O 2 [153,154]. Recently, Tang et al designed a new type of assembled FRET-based nanobiosensor QDs-ConA-β-CDs-AuNPs for the direct determination of glucose in human serum [155].…”

Options for the Development of Noninvasive Glucose Monitoring

“…For enhancement of GOx activity the assembling of a complex with quantum dots of different compounds is possible, for example CdTe. 55 …”

Biosensors Based on Biological Nanostructures

“…Among them is their use as support matrix for the construction of biosensors. A common way to prepare them is to employ a fluorescent compound such as quantum dots and enzymes as receptors physically adhered to these nanostructures, as those developed by Cao et al, (Cao, Ye et al, 2008) or using free enzymes and colloidal quantum dots dissolved in an aqueous solution as those developed by CostaFernandez et al (Costa-Fernandez, Pereiro et al, 2006). Some had aimed at the development of supports that can efficiently incorporate bioreceptors and fluorescent interacting compounds, which is the critical step for the development of biosensors and bioelectronic devices.…”