Abstract: A novel method was developed for the qualitative and quantitative determination of estradiol based on its specific recognition by the DNA aptamer of optimum length as well as the changes in the color and absorbance of colloidal gold before and after aggregation. In this work, colloidal gold particles were prepared and the 75-mer, 35-mer and 22-mer estradiol-specific nucleic acid aptamers were designed for the ultrasensitive colorimetric detection of estradiol. The colorimetric method was based on the fact that the optimal concentration of sodium chloride leads to the aggregation of colloidal gold without the protection of the aptamer, while the colloidal gold does not aggregate under the protection of the aptamer. The results showed that the concentration of estradiol in the range of 13.6?54.4 pg/mL exhibited a good linear relationship with the absorbance ratio (A625 nm/A523 nm) of colloidal gold at 625 nm and 523 nm with a limit of detection (LOD) of 2.7 pg/mL, under the condition of 30 mmol/L sodium chloride and 30 nmol/L 35-mer nucleic acid aptamer. The developed colorimetric sensor had the advantages of high specificity, stability and reproducibility. The practicality of this proposed method was further confirmed through the detection of estradiol in milk samples with LOD of 13.6 pg/mL. Therefore, this colorimetric method will be useful for the rapid and sensitive detection of estradiol in milk products.

Key words: estradiol, colloidal gold, DNA aptamer, colorimetry