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.
Sol-gel and hand milling techniques were used to prepare a lithium iron phosphate-lithium manganese silicate (LiFePO 4 À Li 2 MnSiO 4) hybrid cathode materials. The structural studies from x-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) show that the materials are well crystallized although few impurities were observed in the pristine LiFePO 4 (LFP) and Li 2 MnSiO 4 (LMS) materials. We used graphene to coat the hybrid cathode materials in order to increase its conductivity and enhance the electrochemical performance. The successful reduction of the graphene oxide into graphene nanosheets was confirmed with the results from the Fourier transform infrared (FTIR) and Raman spectroscopy. The morphological analysis indicate that the pristine materials are made of spherical nanoparticles that are slightly agglomerated while the sol-gel-prepared hybrid cathode materials show evenly distributed spherical nanoparticles with minimal agglomeration. The in situ sol-gel technique gave more homogenously mixed material in comparison to the hand milling method and particle sizes of 37 and 23 nm respectively were obtained for the plain, and graphenised sol gel derived hybrid materials. The sol-gel derived hybrid materials are also the most thermally stable giving a total weight loss of 4.5 % and 3.4 % for the plain and graphenised cathodes respectively. While the LFP-LMS hybrid cathode materials performed better electrochemically more than the pristine materials in terms of enhanced current and specific capacities, the graphenised LFP-LMS hybrid cathode materials showed better electrochemical properties compared to those without graphene. This is associated with the presence of graphene nanosheets in these samples. All the results confirmed that the graphenised LiFePO 4 À Li 2 MnSiO 4 hybrid cathode material prepared via in situ sol-gel method performed better than those of the hand milling method.
The hexathienylbenzene-co-poly(3-hexylthiophene-2,5diyl) (HTB-co-P3HT) conducting polymer was synthesized by oxidative co-polymerization of hexathienylbenzene (HTB) and 3-hexylthiophene using iron chloride (FeCl3) as an oxidant. The effect of chlorobenzene, toluene and chloroform on the optoelectronic characteristics of the polymer was investigated. The study revealed that spectroscopic and electrochemical responses of HTB-co-P3HT are affected by the nature of the solvent. The lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) energy levels of HTB-co-P3HT were determined from cyclic voltammetry (CV) and were compared to those of (6,6)-Phenyl C71 butyric acid methyl ester (PC71BM) and it was found that the LUMO energy levels of HTB-co-P3HT in toluene were lower than those for chlorobenzene and chloroform. The electrochemical impedance spectroscopy (EIS) analysis also revealed the thin film of HTB-co-P3HT prepared using toluene as the most conductive. However, the photovoltaic parameters of the HTB-co-P3HT organic photovoltaic cells (OPVs) departed from the favored toluene and noted chlorobenzene as being the advantageous solvent. We obtained a power conversion efficiency (PCE) of 0.48%, fill factor (FF) of 27.84%, current density (JSC) of 4.93 mA.cm−2 and open circuit voltage (VOC) of 0.35 V in chlorobenzene, a PCE of 0.30%, FF of 26.08%, JSC of 5.00 mA.cm−2 and VOC of 0.23 V in chloroform and finally, a PCE of 0.33%, FF of 25.45%, JSC of 5.70 mA.cm−2 and VOC of 0.23 V in toluene.
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