Optimization of the Sensor-Chip Surface in a Capacitive Biosensor for use in Aflatoxin Assays

Abstract: The capacitive biosensor technology can be utilized for the analytical detection of a variety of different compounds. By employing the electrical double-layer principle, it is possible to detect very low concentrations of the target analyte due the methods inherent high sensitivity. This affinity-based capacitive biosensor is a powerful tool also for the analytical detection of low molecular weight compounds. In this work, a specific group of mycotoxins named aflatoxins are targeted. Aflatoxins are low molecular weight molecules produced by certain Aspergillus spp., a group of fungi prone to propagate on food and feed stuff under certain conditions, and thereby invoke toxin contamination. With the high toxicity related to aflatoxin contamination, humans and animals that are ingesting even small amounts of aflatoxin-contaminated food stuff risk severe health issues or death. The high specificity of the capacitive biosensor technique is related to the use of biological recognition elements (but also synthetic variants), where the most commonly used group is antibodies. In this work, both biological and synthetic recognition elements were evaluated to achieve highly sensitive and specific detection of aflatoxins, where the use of gold nanoparticles to increase the surface area of the biosensor transducer proved to significantly aid in increasing the limit of detection of the method. The presented methods showed good result for the detection and quantification of aflatoxin B1.Popular SummaryPathogenic fungi microorganisms produce toxins (i.e., mycotoxins), which are highly poisonous even in very low concentrations. Aflatoxins are considered as one of the most toxic variants and is mainly produced by the fungi Aspergillus flavus and Aspergillus parasiticus. Aspergillus spp. have a tendency to contaminate commodities like nuts and other similar food stuff. Consumption of these contaminated nuts can cause severe liver damage, which in turn can trigger cancer. Due to the small size of the different variants of the aflatoxin molecule (<400 Da) and considering that even extremely low concentrations of the compound are highly toxic to humans, there is clear need for improved sensitive analytical methods both for field settings and for clinical applications. By utilizing biosensing technology (e.g., the capacitive biosensor), highly sensitive detection of aflatoxin is indeed possible. The capacitive biosensor has the advantage of being reusable, do not require sophisticated pre-treatment methods and is cost-effective per analysis. In this thesis work, the affinity-based capacitive sensor was operated with biorecognition molecules like antibodies, synthetic polymers or denatured proteins to create specific sites for detection. Furthermore, combined with nanotechnology (nanoparticles), it was possible to further increase the sensitivity of this system. In this work, we have achieved detection of aflatoxins at concentration levels lower than the permitted levels in food stuff i.e., nuts (e.g., less than 12 µg/kg for aflatoxin B1).The improved techniques for aflatoxin detection developed in this thesis work can indeed help facilitate the detection of aflatoxin at an early stage, preventing consumption of contaminated material and hence aid in the work of avoiding severe health problems.