Choline is employed as cholinergic activity marker in brain tissue in the field of clinical detection of diseases. Although, chromatographic methods and biosensors are the most commonly used techniques for choline detection, there is also an interest in exploring the efficacy of a cost effective non-enzyme based sensor for choline detection. Here, electrochemical sensors based on green synthesized metal oxides (iron (III) oxide nanoparticles) from Callistemon viminalis leaves and flowers extract (Fe3O4NPL and Fe3O4NPF) in combination of functionalized multi-walled carbon nanotube (f-MWCNT) supported on glassy carbon electrodes (GCE/f-MWCNT/Fe3O4NPL and GCE/f-MWCNT/Fe3O4NPF) were fabricated for choline detection. Morphological, structural and optical analysis of the nanocomposites were studied using scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR), X-ray diffractometer (XRD) and ultra violet-visible (UV–vis) spectroscopy accordingly. In contrast, electron transport properties on bare glassy carbon electrode (GCE) and nanocomposite modified electrodes (GCE/f-MWCNT/Fe3O4NPL and GCE/f-MWCNT/Fe3O4NPF) was examined through electrochemical characterization using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Electrochemical oxidation of choline was also studied through CV, EIS, square wave voltammetry (SWV) and chronoamperometry (CA). The result proved that f-MWCNT enhanced the reactivity of Fe3O4NP towards choline oxidation with voltammetric limit of detection (0.83 and 0.36 μM) for choline at GCE/f-MWCNT/Fe3O4NPL and GCE/f-MWCNT/Fe3O4NPF electrodes respectively. Designed sensors proved selective, reproducible, stable and applicable for real sample sensing in choline dietary supplements.

This study investigates in-vitro activities of phytochemicals in Callistemon citrinus against multiresistant foodborne pathogens, alpha-glucosidase enzyme and MCF-7 cancer cell line. Assays were prepared with lyophilized extracts to determine antioxidant capacity, inhibition of a-glucosidase enzyme and growth of foodborne bacteria. Annexin-V detection kit was used for apoptosis detection and FT-IR spectroscopy to confirm structural and functional groups of phytochemicals. Cytotoxicity of the extracts against MCF-7 cells was monitored with xCELLigence Real-Time Cell Analyser. The result from FT-IR analysis gave a peak at 3295 cm À1 wavenumber, confirming the presence of O-H alcohol functional group. FT-IR analysis also showed the presence of different functional groups such as carboxylic acids, aromatics, alkanes, alcohols, aliphatic amines, alkenes and amine groups in the extracts. Callistemon exhibited strong antioxidant capacities with EC 50 values of 0.474 ± 0.03 and 0.787 ± 0.15 mL sample/g of 2,2-diphenyl-1-picrylhydeazyl (DPPH) from leaf and flower extracts, respectively. Growth inhibition of most gram-positive foodborne bacteria by phytochemicals from flower extract appeared more promising as an alternative antimicrobial agent for food preservation. IC 50 value of 3.69 ± 0.61 lg/mL obtained from leaf extract showed its inhibitory potential against a-glucosidase enzyme for managing diabetes type-2. A dose response obtained from real-time monitoring with xCELLigence system indicated higher cytotoxicity of the extracts against MCF-7 cell line at !200 lg/mL concentrations within 24 h of incubation. The versatility of phytochemicals in Callistemon observed in this study signifies its potential for enhancing feed or food functionality, moderating blood glucose level and inhibiting the growth of foodborne pathogens or invasive carcinoma in man.

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Less toxic, environmentally safe green-mediated iron (III) oxide nanoparticles (Fe3O4-NP) synthesized using Callistemon viminalis (C. viminalis) leaf (Fe3O4-NPL) and flower (Fe3O4-NPF) extracts is reported in this work for the first time. Total flavonoids and phenols present in the plant extracts were determined. Characterization of the nanoparticles was carried out using Fourier transform infrared (FTIR) spectroscopy, ultraviolet–visible spectroscopy (UV–VIS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Malvern zeta sizer. Other properties of the nanoparticles were investigated using the thermogravimetric analyser and cyclic voltammetry. The average particle sizes obtained for Fe3O4-NPL and Fe3O4-NPF were 17.91 nm and 27.93 nm, respectively. Fe3O4-NPL exhibited an excellent electrochemical activity when compared with Fe3O4-NPF based on a stability study using cyclic voltammetry and regression value. Additionally, Fe3O4-NPF displayed excellent antimicrobial activity against Bacillus cereus, Salmonella enteritidis, and Vibrio cholerae with zones of inhibition of 13, 15, and 25 mm, respectively. Simple, cheap, and less toxic green-mediated iron (III) oxide nanoparticles synthesized from C. viminalis leaf (Fe3O4-NPL) and flower (Fe3O4-NPF) extracts hold the potential of being used to control the activity of pathogenic bacteria of health importance and as an electrochemical sensor for both biological and environmental analytes.

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