Abstract
The thermal degradation related to stability in long-term storage of a carbon nanotube-based biosensor has been investigated. The effect of storage temperature on detachment and denaturation of glucose oxidase (GOx) biocatalyst has been proved. The carbon nanotubes (CNTs) coated with polyethyleneimine (PEI) as entrapping polymer to attract more GOx to form a durable and layered CNT/PEI/GOx structure is used for long-term storage to minimize GOx detachment from the structure and minimize the possibility of enzyme and protein denaturation. After 120 days, the glucose response of the CNT/PEI/GOx biosensor stored under 4°C is preserved up to 66.7% of its initial value, while under a 25 °C storage the response is maintained up to 41.7%. The enzyme coverage activity of CNT/PEI/GOx stored at 4 °C and 25 °C has decreased by 31.1% and 51.4%, respectively. Denaturation and detachment of GOx are the common causes of thermal degradation in biosensors under improper storage temperatures, but the presence of PEI in the structure can slow-down these phenomena. Moreover, the electrons transfer constant of CNT/PEI/GOx biocatalyst stored at 4 °C and 25 °C were 7.5 ± 0.5 s−1 and 6.6 ± 0.3 s−1, respectively, indicating that also electrons mobility is damaged by detachment and denaturation of enzyme protein and the detection of glucose from the glucose oxidation reaction (GOR) is compromised.
Highlights
Carbon Nanotubes (CNTs) has long been known as an attractive material in various applications, especially sensors or biosensors due to its unique mechanical and electronic properties [1]
◦ C and 25 ◦ C decreased by 19.09% and 26.22%, respectively, current density of carbon nanotubes (CNTs)/Glucose Oxidase (GOx) stored at storage process
120 days decreasedcan bybe and 48%, respectively its initial value, while activity, but long term storage below is expensive, and the possibility to reduce degradation by in CNT/PEI/GOx decreased by 12.63% and 33.27% when stored at 4 C and 25 C, respectively, preparing suitable catalytic structures, in whichactivity
Summary
Carbon Nanotubes (CNTs) has long been known as an attractive material in various applications, especially sensors or biosensors due to its unique mechanical and electronic properties [1]. A deeper characterization about long-term stability, the effect of storage temperature, the decrement of electrochemical properties, and the protection strategies to preserve biocatalyst activity is needed to deeply understand the statement above and suggest protocols to manage these materials for longer times. Using higher storage temperatures for a long time will increase the probability of denaturation of proteins and thermal degradation of the biosensor due to the detachment of enzymes from the supporting structure storage costs are sensibly lower, but stability and durability are not ensured. A glucose biosensor based on CNT, GOx and PEI is investigated and electrochemical performances after 120 days of storage at 4 ◦ C or 25 ◦ C are measured and discussed. The high relative activity, the long term bonding effect of PEI, the simple biocatalyst structure, and durability support the proposed novelty of this work. All electrochemical characterizations were measured at the initial day and final day, to quantify the degradation of biocatalyst properties over time
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