Aflatoxins form a class of potent carcinogens that contaminate a wide range of food products and can be fatal to humans and livestock. We have designed cysteamine-capped CdS quantum dots (QDs) to serve as aflatoxin photodetectors for use in agricultural industries. Water-soluble CdS QDs are synthesized through growth in a poly(vinyl alcohol) matrix using a chemical precipitation method. The prepared QDs are then characterized with X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), dynamic light scattering (DLS), and transmission electron microscopy (TEM) analyses. The obtained results revealed that these CdS QDs have a 1-to 2-nm crystalline size, hexagonal wurtzite structure, and spherical morphology with a diameter less than 10 nm. Photoluminescence spectroscopy (PL) is performed to study the CdS QDs interactions with a standard solution of aflatoxins (B1, B2, G1, and G2 in a ratio of 5:1:5:1) in order to determine their effectiveness as aflatoxin detectors. A green emission peak is observed at 508 nm, with an intensity enhancement positively correlated with total aflatoxin concentration. The lower limit of detection for total aflatoxin concentration is found to be 0.05 ppb, well below international contamination allowances for food products. PL variations with aflatoxin concentration are best described by a Langmuir-type equation in the concentration range of this study (2.4-48 ppb).
In the present research, water soluble thioglycolic acid-capped CdS quantum dots (QDs) were synthesized by chemical precipitation method. The characteristics of prepared quantum dots were determined using X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). The obtained results revealed that CdS QDs have 5.60 nm crystallite size, hexagonal wurtzite structure and spherical morphology with less than 10 nm diameter. The photoluminescence (PL) spectroscopy was performed in order to study the effect of the presence of starch solutions. Blue emission peaks were positioned at 488 nm and its intensity quenched by increasing the concentration of starch solutions. The result of PL quenches in range of studied concentrations (0-100 ppm) was best described by Michaelis-Menten model. The amount of Michaelis constant (Km) for immobilized α-amylase in this system was about 68.08 ppm which showed a great tendency of enzyme to hydrolyze the starch as substrate. Finally, the limit of detection (LOD) was found to be about 2.24 ppm.
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