Abstract
We report the preparation of poly (propylene imine) dendrimer (PPI) and CdTe/CdSe/ZnSe quantum dots (QDs) as a suitable platform for the development of an enzyme-based electrochemical cholesterol biosensor with enhanced analytical performance. The mercaptopropionic acid (MPA)-capped CdTe/CdSe/ZnSe QDs was synthesized in an aqueous phase and characterized using photoluminescence (PL) spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy, transmission electron microscopy (TEM), X-ray power diffraction (XRD), energy dispersive X-ray (EDX) spectroscopy. The absorption and emission maxima of the QDs red shifted as the reaction time and shell growth increased, indicating the formation of CdTe/CdSe/ZnSe QDs. PPI was electrodeposited on a glassy carbon electrode followed by the deposition (by deep coating) attachment of the QDs onto the PPI dendrimer modified electrode using 1-Ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC), and N-hydroxysuccinimide (NHS) as a coupling agent. The biosensor was prepared by incubating the PPI/QDs modified electrode into a solution of cholesterol oxidase (ChOx) for 6 h. The modified electrodes were characterized by voltammetry and impedance spectroscopy. Since efficient electron transfer process between the enzyme cholesterol oxidase (ChOx) and the PPI/QDs-modified electrode was achieved, the cholesterol biosensor (GCE/PPI/QDs/ChOx) was able to detect cholesterol in the range 0.1–10 mM with a detection limit (LOD) of 0.075 mM and sensitivity of 111.16 μA mM−1 cm−2. The biosensor was stable for over a month and had greater selectivity towards the cholesterol molecule.
Highlights
Cholesterol ((3β)-cholest-5-en-3-ol) is a fat-like organic biomolecule found in all cells and that is naturally produced by the liver and the intestines
The glassy carbon electrode (GCE) modified with quantum dots (QDs) (Figure 5Bi) and PPI (Figure 5Bii) did not show any significant redox current because there was no electrocatalytic reaction with the cholesterol due to the absence of the enzyme (ChOx)
Fluorescent water-soluble mercaptopropionic acid (MPA)-capped CdTe/CdSe/ZnSe core/multishell quantum dots were successfully synthesized in aqueous phase and characterized using various analytical techniques
Summary
Cholesterol ((3β)-cholest-5-en-3-ol) is a fat-like organic biomolecule found in all cells and that is naturally produced by the liver and the intestines. Dendrimers have been exploited as a matrix or immobilisation layer to provide a biocompatible environment for biomolecules in biosensors This is due to their unique properties such as: Analogues to small enzymes in terms of their size, functional complexity and structural precision, biocompatibility, cationic nature and multiple attachment sites [25,30,31]. Dendrimers such as poly (propylene imine dendrimer) dendrimer (PPI) and poly (amido amine) have been used as immobilisation layer in different types of biosensors for DNA, toxins, cholera, cancer biomarker etc. The QD is expected to improve enzyme loading while the dendrimer provides a platform for biocompatibility and immobilization chemistry suitable for the enzyme attachment
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