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Title: Electrochemical aptasensor for the detection of mycotoxins in food samples by experimental and computational methods
Authors: Kunene, Kwanele 
Keywords: Electrochemical;Aptasensors;Mycotoxins;Food samples;Computational methods;Detection
Issue Date: 2021
Mycotoxins are secondary metabolites of fungi that are present in various foodstuff and
feed commodities. A large number of mycotoxins exist, however only a limited number
represent a major damages and toxic properties. Amongst them, the aflatoxins and
ochratoxins are deemed to be the most poisonous and extensively circulated in the world and
then, represent a real hazard to both human and animal. Depending on several factors like the
consumption levels, exposure time, mechanisms of action, digestion and defense
mechanisms, mycotoxins stimulate a wide spectrum of toxicological effects leading to both
acute and chronic diseases, liver and kidney failure, skin rash, cancer, immune suppression,
birth defects or even death.
To address the harmful impact of mycotoxin contaminants in food and feed, health authorities
in various countries world-wide have established guidelines in order to protect human and
animal from the possible damages instigated by these toxins. Authorities such as the
European Commission, US Food and Drug Administration (FDA), World Health
Organization (WHO) and the Food and Agriculture Organization of the United Nations
(FAO) set up maximum level regulations for main mycotoxins in foods and feeds. To
accomplish the expectations of these regulation levels, there is a great need for the
development and validation of modern, uncomplicated, rapid, and detailed methodologies for
the detection of toxins.
In this study, various approaches for the rapid, inexpensive and ultrasensitive biosensors for
the detection of two major mycotoxins were developed. The electrochemical-based
aptasensor and immunosensor were developed for the determination of aflatoxin B1 (AFB1)
and ochratoxin A (OTA) in different food products. The fabricated biosensors demonstrated
good practical analytical feasibility for mycotoxins detection in real samples such as WeetBix, yoghurt, coffee and in wine samples with excellent recoveries and RSD values. To avoid
fouling on the sensor surface by the constituents present in real samples, the carbon screen
printed electrode (C-SPE) and carbon felt electrode (CFE) surfaces were modified with
different nanomaterials such as silver nanoparticle (AgNPs), palladium nanoparticles
(PdNPs), palladium doped boron nitride (PdNPs-BN) and titanium nanoparticles doped with
boron nitride BN-TiO2. In addition, the aptamers and antibodies were immobilized on the modified electrode in order to enhance the selectivity of the sensor towards the detection of
OTA and AFB1.
The electrochemical aptasensor for OTA permitted for highly sensitive detection in Weet-Bix
with a wide linear range (0.002 - 0.016 mg L-1) and limit of detection of 7×10-4 mg L-1. It is
worth prominence that it is the first time that carbon screen printed electrode (C-SPE)
modified with AgNPs was used, opening new pathways for highly precise analysis.
Experimental results were further supported computationally for a better understanding of the
interaction between the aptamer and the analytes. Computational results were in good
agreement with experimental results. The same procedure was also established in
voltammetric detection of AFB1 using CFE modified with BN-TiO2 (CF/BN-TiO2). A wide
concentration range of 2.5 - 20 ng mL-1 with an excellent LOD of 0.002 ng mL-1 for AFB1
was obtained. For the case study of wine samples tested for AFB1 detection, a simple but very
effective pretreatment method was effectively applied. The addition of acetonitrile to the
wine reduces the non-specific interactions that might be accountable for inactivation of
antibody and blocking of the sensor surface. Furthermore, the PdNPs-BN enhanced the
electrical signal and the sensor sensitivity. Attained results allowed for AFB1 detection at
concentrations range from 1.0 - 10 ng mL-1 with limit of detection of 0.832 ng mL-1
. In the
case study of the electrochemical immunosensor for the detection of OTA in coffee, a linear
detection range of 0.5 - 20 ng mL-1
was achieved with LOD of 0.096 ng mL-1
The fabricated aptasensors and immunosensors in this study combines the most desirable
characteristics of a good biosensor such as high sensitivity, inexpensive, rapid, and simple but
portable method make proposed approaches an important and very promising tools for
extensive biosensing applications.
Submitted in fulfillment of the requirements of the degree of Doctor of Philosophy in Chemistry at the Durban University of Technology, 2021.
Appears in Collections:Theses and dissertations (Applied Sciences)

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