Faculty of Applied Sciences

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Development of electrochemical sensors for the detection of mycotoxins in food matrices using functionalised nanocomposites
(2024-05) Naidoo, Lyndon; Bisetty, Krishna; Meier, Florian; Uwaya, Gloria Ebube
The analysis of pathogens in foods is of critical importance to ensure consumer safety and quality assurance, as contaminants pose serious risks to public health. Mycotoxins are naturally occurring carcinogenic toxins that arise from specific strains of fungi as they contaminate food. They are found in a wide variety of grains, cereals, and dairy products, causing cancer in both humans and animals. Thus, there is a growing demand for simple, sensitive and inexpensive sensors for mycotoxin detection in lieu of conventionally employed large-scale instrumentation. In this study, the development of electrochemical sensors for the detection of aflatoxin B1 (AFB1), zearalenone (ZEN) and ochratoxin A (OTA) in foods was investigated and presented as three case studies, respectively. In the first case study, an ultrasensitive aptasensor was developed for the indirect detection of AFB1 in the presence of a ferri/ferrocyanide ([Fe(CN)6]3-/4-) redox probe solution. The sensor was constructed by immobilizing an anti-AFB1 aptamer (Apt) to a carboxylated multiwalled carbon nanotube (cMWCNT) and iron oxide (Fe3O4) nanoparticle (NP) composite using a glassy carbon electrode (GCE). This resulted in the development of the GCE/cMWCNTsFe3O4 NP/Apt sensor. An electrochemical response was exhibited from AFB1 applying cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV), respectively, utilizing a [Fe(CN)6]3-/4- redox probe prepared in phosphatebuffered saline (PBS) solution with reference to the Ag/AgCl reference electrode under optimized conditions. DPV findings reported very low limits of detection (LOD) and quantification (LOQ) of 0.43 fg mL-1 and 1.44 fg mL-1 respectively in comparison to current literature, over a calibration range of 0.50 fg mL-1 to 5.00 fg mL-1. For real sample analysis, excellent spike recoveries from 95% to 105% were obtained for corn and rice flour. Density functional theory (DFT) was used to propose a reaction scheme by ascertaining the electronic properties of the redox-active functional groups of AFB1. This supported the experimental anodic response findings of DPV. The second case study focused on how PEGylated Fe3O4 NPs and cMWCNTs fabricated on a GCE could be used for the design of an electrochemical sensor for ZEN analysis. The qualitative and quantitative analyses of ZEN were completed using CV, EIS and DPV, respectively, under optimized conditions in a sodium phosphate buffer solution. The developed sensor reported significantly low LODs and LOQs of 0.34 fg mL-1 and 1.12 fg mL-1 respectively, over a calibration range of 1.00 fg mL-1 to 10.00 fg mL-1 by DPV. Excellent spike recoveries ranging from 92% to 106% were obtained for rice and corn flour. The Monte Carlo (MC) adsorption simulation studies predicted the strong interaction of ZEN with the constructed sensor. In the final case study, an OTA electrochemical sensor was designed using a nickel metalorganic framework (Ni-MOF) and carboxylated reduced graphene oxide (cRGO) on a GCE. The detection of OTA was achieved under optimized conditions in PBS solution with the developed GCE/Ni-MOF/cRGO electrode, employing CV, EIS and DPV as electrochemical tools. Applying DPV, the sensor reported very low LODs and LOQs of 3.29 fg mL-1 and 10.97 fg mL-1 respectively, over a calibration range of 10.00 fg mL-1 to 90.00 fg mL-1. Regarding real sample analysis, excellent spike recoveries from 95% to 105% were obtained for corn and rice flour. Molecular dynamics (MD) studies predicted that the Ni-MOF exhibited a strong electrostatic interaction with the OTA analyte, in agreement with the experimental findings. The synthesized nanomaterials (cMWCNTs-Fe3O4 NP, PEG-Fe3O4 NPs/cMWCNTs, and NiMOF/cRGO) utilized in this study were characterized by an array of techniques, including single particle inductively coupled plasma-mass spectrometry (spICP-MS), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), multidetector asymmetrical flow field-flow fractionation (AF4), and Fourier transform infrared spectroscopy (FTIR). Finally, computational modelling studies were undertaken to establish a synergy with the experimental approaches employed in each case study. These methodologies included DFT, docking studies, MC adsorption and MD simulations, which were aimed at predicting and assessing the atomic and molecular interactions between the mycotoxins and their respective electrode systems.
Ionic liquid based high performance electrochemical sensor for ascorbic acid in various foods and pharmaceuticals
(Elsevier, 2016-07-18) Kumar, Bhajanthri Natesh; Arumugam, Vasanthakumar; Chokkareddy, R.; Redhi, Gan G.
In the present study, 1-butyl-3-methyl imidazolium tetra ﬂuoroborate ionic liquid (IL), boron nitride (BN) and magnetite nanoparticles (Fe3O4NPs) based nanocomposite (IL-BN-Fe3O4NPs) was successfully synthesised and used to fabricate glassy carbon electrode (GCE) for the determination of ascorbic acid (AA). The nanocomposite was characterized by Fourier transformation infrared spectroscopy (FTIR), x-ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM), electron diffraction spectroscopy (EDS) and transmission electron micros-copy (TEM) techniques to observe the surface morphology. Cyclic voltammetry (CV) was performed to assess the electrochemical performance of IL-BN-Fe3O4NPs/GCE towards ascorbic acid (AA) in 0.1 M phosphate buffer solu-tion (PBS) at pH 7. The CV results obtained reveal that the signiﬁcant enhancement of anodic peak current with increased sensitivity and conductivity. The differential pulse voltammetric results obtained indicates the linear increment of electrochemical signals with an increase in the concentration of AA in the range of 1–12 μM. Based on the calibration plot, limit of detection and limit of quantiﬁcation were calculated and found to be 0.042 and 0.139 μM respectively. The electrochemical sensor showed outstanding sensitivity, selectivity, repeat-ability and stability. In addition to this IL-BN-Fe3O4NPs/GCE sensor was practically applied for the routine analysis of AA in various food and pharmaceutical samples.
Fabrication of copper nanoparticles decorated multiwalled carbon nanotubes as a high performance electrochemical sensor for the detection of neotame
(Elsevier, 2015) Bathinapatla, Ayyappa; Kanchi, Suvardhan; Singh, Parvesh; Sabela, Myalowenkosi Innocent; Bisetty, Krishna
A highly sensitive and novel electrochemical sensor for the detection of neotame using differential pulse voltammetry with a modiﬁed glassy carbon electrode is presented. The method was further customized by the fabrication of the electrode surface with copper nanoparticles–ammonium piperidine dithiocar-bamate–mutiwalled carbon nanotubes assimilated with β-cyclodextrin. The multiwalled carbon nano-tubes assimilated with β-cyclodextrin/glassy carbon electrode exhibited catalytic activity towards the oxidation of neotame at a potential of 1.3 V at pH 3.0. The transmission electron microscopy, thermogravimetric analysis, frontier transform infrared spectroscopy and cyclic voltammetry were employed to characterize the electrochemical sensor. The sensitivity and detection limits of the electrode increased two-fold in contrast to the β-CD-MWCNTs/GCE sensor. The developed method was successfully applied for the determination of neotame in food samples, with results similar to those achieved by our modiﬁed capillary electrophoresis method with a 96% conﬁdence level.

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