Determination of total aflatoxin using cysteamine-capped CdS quantum dots as a fluorescence probe

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).