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Here, L- and D-cysteine-functionalized graphene quantum dots (L-/D-cys-GQDs) were designed with the aim of obtaining a selective fluorescent nanosensor to detect L-morphine.Citric acid was pyrolyzed to synthesize the GQDs, which were then functionalized with chiral L- and D-cys species using a thiol-ene click reaction between sulfur group of cysteine species and C=C double bonds of GQDs.Energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopies (XPS) provides elemental anal. data which approved the presence of sulfur and nitrogen elements of L- and D-cysteine species on the surface of GQDs.Transmission electron microscopy (TEM) showed that the particle size of the modified GQDs ranges from 2 to 4.2 nm.The results of fluorescence spectroscopy showed that upon functionalization of GQDs with L-/D-cys the fluorescence intensity decreases as a result of Forster resonance energy transfer (FRET) mechanism.Interestingly, in the presence of L-morphine, the fluorescence intensity of D-cys-GQDs was selectively turned on as the FRET mechanism is ceased between the cysteine species and GQDs.Addnl. tests demonstrated that this nanosensor cannot interact with other drugs like methamphetamine or ibuprofen.As a result, it can serve as a cheap and precise nanosensor for identifying low quantities of L-morphine.

01 Jan 2025·Analytical Biochemistry

Innovative approaches in invertase immobilization: Utilizing green synthesized zinc oxide nanoparticles to improve biochemical properties

Article

Author: Darvishi, Elahe ; Ghollasi, Marzieh ; Sadi, Somayeh ; Eskandari, Khadijeh

Invertase enzyme can effectively improve the taste, color, and durability of these products. Various methods have been proposed to increase the stability and efficiency of enzymes. One of the most important is enzyme immobilization, which can be implemented on different materials. The purpose of this study was to immobilize the invertase enzyme on the surface of green synthesized zinc oxide nanoparticles and to investigate its biochemical properties. The enzyme immobilization was confirmed by SEM and Raman spectroscopy. Then, the biochemical characteristics, such as optimal pH and temperature, thermal stability, and storage stability of free and immobilized enzymes, were determined. The results of SEM showed that the diameter of synthesized nanoparticles was about 60 ± 5 nm. FTIR of immobilized invertase confirmed the immobilization process. The immobilization efficiency was determined to be 72 %. Immobilized enzyme showed higher thermal stability at 40 and 50 °C. Immobilized enzyme could be used 8 times in optimum condition. Also, an Examination of the kinetic parameters of the immobilized enzyme compared with those of the free enzyme showed a decrease in the maximum velocity of the enzyme. It seems that the immobilized invertase has improved characteristics for application in different industries.

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