An electrochemiluminescence aptamer sensor for chloramphenicol based on GO-QDs nanocomposites and enzyme-linked aptamers

In this paper, CdS quantum dots (QDs) were synthesized. Positively charged poly(diallyldimethylammonium chloride) (PDDA) and negatively charged CdS quantum dots were sequentially adsorbed on the surface of graphene oxide (GO). The nano-luminescent materials GO-QDs were prepared and characterized by UV-Vis absorption spectroscopy, fluorescence spectroscopy and transmission electron microscopy. The GO-QDs were then modified on the surface of glassy carbon electrode (GCE). Chloramphenicol aptamer (apt) of 5'-end modified biotin hybridized with the aptamer complementary strand (cDNA) of 5'-end modified amino group into double-stranded DNA (dsDNA). The double-stranded DNA was bonded onto the surface of GO-QDs modified electrode. When the electrode was incubated with streptavidin - labeled horseradish peroxidase (SA-HRP), the biotin modified at the end of the chloramphenicol aptatner can specifically bind directly to the streptavidin labeled HRP. Therefore, HRP was bonded to the surface of the electrode. Hydrogen peroxide was used as the co-reactant of the QDs. HRP can thereby consume hydrogen peroxide and can weaken the electrochemiluminescence intensity. Chloramphenicol in solution can specifically bind to the aptamer to form a composite and to unwind the dsDNA. Then the composite was detached from the surface of the electrode. HRP also left the electrode surface along with the aptamer, so that the electrochemiluminescence signal was significantly enhanced. The electrochemiluminescence intensity of the sensor showed a linear correlation with the logarithm of chloramphenicol concentration. The linear range was 1.0 x 10(-12)-1.0 x 10(-7) M, the detection limit is 0.5 pM. The reproducibility, stability and specificity of the sensor were also studied. The sensor was used for the determination of chloramphenicol in samples and satisfactory results were obtained. (C) 2020 Elsevier B.V. All rights reserved.