Fabrication Of Fluorescence Aptasensing System Based On CdZnTe Quantum Dots And Its Applications In Mycotoxins Detection

For comparison with their binary counterparts,ternary alloyed quantum dots(QDs)exhibit much narrower emission,broader excitation wavelength,better thermostability and photostability,and higher fluorescent quantum yield.In this paper,mycotoxin aptamers are used as recognition elements,and a series of nanomaterials such as CdZnTe QDs,carbon dots(CDs),gold nanoparticles(AuNPs),and SiO2 nanospheres,MoS2 nanosheets are used as fluorescence labels or DNA strands carriers,to develop a series of fluorescent aptasensing systems for sensitive detection of aflatoxin B1(AFB1)or/and ochratoxin A(OTA).In addition,a fluorescence chemical sensor was also constructed using different ligands-capped CdZnTe QDs for the sensitive detection of metal ions Ag+ or Fe2+.The specific research contents are shown as follows:1.A one-step hydrothermal route was used to prepare 3-mercaptopropionic acid(MPA)-caped ternary CdZnTe QDs.When benchmarked against their binary counterpart CdTe QDs,they possessed enhanced fluorescence intensity.On this bais,a target-driven switch-on fluorescence aptasensor for trace AFB1 determination has been developed by employing the fluorescence resonance energy transfer(FRET)between the CdZnTe QDs and Au nanoparticles(AuNPs)pair.Specifically,amino group-functionalized aptamers against AFB1 were firstly labelled with the CdZnTe QDs donors coated on silica nanospheres while the AuNPs acceptors were bioconjugated with the thiol group-modified complementary DNA(cDNA)of aptamer.By taking advantage of the DNA hybridization of aptamer and cDNA.,the CdZnTe QDs(energy donor)and AuNPs(energy acceptor)were brought into close proximity,thereby leading to the occurrence of FRET during the aptasensor fabrication.When the aptasensor was incubated with AFB1,the specific binding between aptamer and target resulted in the detachment of AuNPs acceptors.This behavior would disturb the FRET process and led to the subsequent fluorescence recovery of CdZnTe QDs.A good linear relationship between fluorescence intensity of CdZnTe QDs and the concentration of AFB1 over a wide range of 50 pg mL-1-100 ng mL-1,and the limit of detection was 20 pg mL-1.2.Carbon dots(CDs)and CdZnTe QDs(QDs)were prepared via a simple hydrothermal route,while MoS2 was prepared by a modified liquid exfoliation method,indicating the simple preparation step of aptasensor.The working principle of the aptasensor is based on the absorption action of aptamers and MoS2 and the specific binding action between aptamers and targets.In the absence of AFB1 and OTA,the aptamers were adsorbed on the MoS2 surface,causing the quenching of fluorescence due to the FRET principle.In the presence of AFB1 and OTA,aptamers was specific for targets,leading to the distance between MoS2 and CDs(QDs)and causing the recovery of fluorescence.Furthermore,the aptasensor exhibited a wide detection range of 0.01-10 ?g mL-1 for AFB1 and 0.02-5 ?g mL-1 for OTA.The limit of detection is 3 pg mL-1 and 7 pg mL-1 for AFB1 and OTA,respectively.3.Three kinds of CdZnTe QDs with different ligands(N-acetyl-L-cysteine,L-cysteine and mercaptopropionic acid)have been prepared through hydrothermal route.For each kind of thiol capped QDs,different-colored CdZnTe QDs were obtained by controlling the various reaction times in the same reaction situation,accompanied by changes in the fluorescence spectrum.Based on the selective response of Lcys-CdZnTe QDs to Ag+ and MPA-CdZnTe QDs to Fe2+.Lcys-CdZnTe QDs and MPA-CdZnTe QDs were chosen as the fluorescence sensors for Ag+ and Fe2+ determination respectively.It was found that there was a good linear relationship between fluorescence intensity of Lcys-CdZnTe QDs and the concentration of Ag+over a range of 0.032-16 ?M.The limit of detection is 0.01 ?M.Meanwhile,good linearity between fluorescence intensity of MPA-CdZnTe QDs and the concentration of Fe2+ was obtained over a range of 0.64-48 ?M.The LOD is 0.01 ?M.The fluorescence color of Lcys-CdZnTe QDs and MPA-CdZnTe QDs changed with the increase of Ag+ and Fe2+ concentrations.Based on this phenomenon,semi-quantitative detection of Ag+ and Fe2+ by naked eyes is realized.