Sensitive Metal Oxide-Clay Nanocomposite Colorimetric Sensor Development for Aflatoxin Detection in Foods: Corn and Almond

Abstract

The work reports on zinc oxide bentonite nanocomposite (ZnOBt) chemical route synthesis, characterization, and investigation of curcumin (Cur) functionalization for a label-free colorimetric detection of total aflatoxins (AFs) in foods. XRD of ZnO nanoparticles (NPs) confirmed the wurtzite structure (2θ = 36.2°) and that of ZnOBt showed the intercalated interlayer composite phase. The Debye–Scherrer relation calculated the crystallite size as 20 nm (ZnO) and 24.4 nm (ZnOBt). Surface morphology by SEM exhibited flower-like hexagonal, rod-shaped ZnO NPs on the bentonite surface. Colorimetric reaction involved two-stage redox reactions between ZnOBt and dye Cur followed by AFs phenolic group and Zn(Cur)OBt. Cur gets oxidized at its diketone moiety in the presence of ZnOBt to form a red colored complex Zn(Cur)OBt, which further scavenge protons from AFs phenolic group, and gets oxidized to AFs-Zn(Cur)OBt (yellow). Binding of AFs-Zn(Cur)OBt is characterized by FT-IR ascribed to C–H bending (1966.615 cm –1 ), O–H stretching (3256.974 cm –1 ), and C=O stretching (1647.362 cm –1 ). 1 H NMR chemical shifts (δ) (ppm) showed an increase in proton at the aliphatic region (0 to 4.4) while removal of proton in ether at 4.4 to 6 regions. Job plot calculation using UV–Vis data resulted in a higher total AF binding coefficient of Zn(Cur)OBt ( K a = 3.77 × 10 6 mol –1 L) compared to Zn(Cur)O ( K a = 0.645 × 10 6 mol –1 L) as well as a molar ratio of 1:1 by the Benesi–Hildebrand plot equation. Corn and almond food samples showed the total AFs LOD of 2.74 and 4.34 ppb, respectively. The results are validated with standard LC/MS-MS in compliance with MRL value as per the regulatory standard (EU).The NP-based method is facile and rapid and hence can be utilized for onsite detection of total AFs in foods.

Improving the functionality of biodegradable food packaging materials via porous nanomaterials

“…Reports suggest that the catalytic activity of metal oxides increases when they are immobilized on bentonite as a natural clay with a high surface area. Khansili and Murali Krishna (2021) fabricated a label-free colorimetric biosensing platform using ZnO 2 bentonite nanocomposite (ZnOBt) to detect the total aflatoxin concentration in corn and almond samples in two-stage redox reactions between ZnOBt and dye Cur. The LOD of aflatoxin in corn and almond was determined as 2.74 and 4.34 ppb, respectively.…”

A controllable staining colorimetric method based on carboxylated cellulose membranes for early-warning and semi-quantitative detection of aflatoxins in water

“…Corn is an essential raw material for animal feed, and many countries have reported aflatoxin contamination in corn. 38,39 To evaluate the practicability of this sensing system, the sensing strategy, addition, and recovery experiments for determining the concentration of total AFs in corn samples were carried out. After adding different quality aflatoxins to 4 ground fresh corn samples, the spiked samples with mixed AFs were pretreated by liquidliquid extraction separation.…”

Gaseous Heptanethiol Removal by a Fe3+-Phenanthroline–Kaolinite Hybrid Material

“…Usually, these materials are grouped based on the type of host (i.e., the layered mineral) and guest molecule involved in the interaction. Three main types of functionalized layer silicates can be identified, namely, (i) organoclays, which are layered silicates (typically smectites) bound to an organic molecule (or to an organo-metallic complex) that imparts peculiar properties to the modified minerals; − (ii) pillared clays, which are layered silicates intercalated with small organic or inorganic complexes (i.e., “pillars”), partially filling the interlayer space; − and (iii) clay mineral-nanocomposites, which are fine-particulate materials, heterogeneous at the nanoscale level, made at least from one clay mineral and from other materials such as polymers, pharmaceuticals, inorganic molecules, or carbon. − …”