## 1 Introduction  
Aflatoxins are cancerous secondary metabolites from _Aspergillus flavus_ and _Aspergillus parasitic_. Due to their high toxicity and carcinogenic potential, they are a high concern for the safety of food worldwide. They can be found in various agricultural products such as grains, nuts, spices, etc. Based on chromatographic and fluorescence characteristics, all aflat known to date can be classified into 18 different types, but there are four major naturally occurring aflat: B1, B2, G1, and G2. A third subset, M1 and M2, arise as metabolic products when dairy cattle eat B contaminated grains [1; 2; 3; 4]. Among them, aflatoxin B1 (AFB1) is the most common and most widespread [5; 6] in the world and accounts for 75% of all aflat contamination of food and feeds [7].  
Aflatoxins are widely distributed in nature and are commonly found as contaminants in human food, particularly in cereals, oilseeds, tree nuts, and even milk. They are mutagenic in bacteria and infect cereals during harvest and storage. The host plants are susceptible to _Aspergillus_ infection after prolonged exposure in high humidity environments or damaged by prolonged drought conditions. Aflatoxins can be toxic to humans and animals causing liver damage, abnormalities, mutations, and cancer, and when in high doses, aflat can be fatal [8].  
Vietnam is a country with a tropical climate which is a favorable condition for the growth of molds such as Aspergillus flavus and A. Parasiticus. There have been great losses for post-harvest and storage agricultural products, in which the cause of mold accounts for a significant part due to the effects of the tropical climate. When molds grow on grains, the molds not only use the nutrients such as protein, lipid, vitamins, etc., but they also produce toxins that are particularly dangerous to human and animal health [9].  
In Vietnam, maize is the second most important staple crop for humans after rice. It is a substitute for rice, especially for people in rural and mountainous areas. It is also the major component of feeds for Vietnam's livestock industry. Unfortunately, maize is also a good substrate for mycotoxins producing fungi, especially those producing aflat. Therefore, from a food safety point of view, it is important to assess and control the levels of aflat in human food and animal feeds [10,11].  
There are many methods to detect aflat such as thin-layer chromatography (TLC), liquid chromatography (LC), radioimmunoassay (RIA), enzyme-linked immunosorbent assay (ELISA), immunoaffinity column assay (ICA), and mass spectrometry imaging (MSI) [12]. Conventionally, they often employ expensive equipment requiring trained personnel to operate. A lot of time is also required in preparing the samples besides using large amounts of chemical reagents. The method of using a quick test kit gives low accuracy. Fast, sensitive, and inexpensive detection methods, therefore, have been developed such as fluorescence spectroscopy [13, 14, 15] or Fourier transform infrared spectroscopy (FTIR) [16].  
In this paper, the detection of AFB1 using fluorescence resonance energy transfer (FRET) method wherein AFB1 acts as a donor, CdSe/ZnS quantum dots (QDs) acts as an acceptor will be presented. The effect of FRET is that the fluorescence intensity and fluorescence lifetime change so that the AFB1 concentration can be determined from changes in fluorescence lifetime or fluorescence intensity. A fluorescence lifetime calibration curve versus AFB1 concentrations was also established. Test results of AFB1 determination in maize in Vietnam by the FRET method are consistent with the results of aflat determination by HPLC in ppM concentration.