Electrochemical Biosensor For UO₂²⁺ Based On Special DNAzymes And AuNPs

DNAzymes is a kind of DNA molecules which have high catalytic activity andrecognition ability. DNAzymes active site can distinguish the substrate from theatomic level and catalyze similar reaction, so the DNAzymes is often used as signalconversion tool. Gold nanoparticles (AuNPs) exhibit many advantages, such as largesurface area, high surface free energy, easy conjugation chemistry, good conductivityand biocompatibility. AuNPs can effectively retain the activity of biomolcules andenhance the stability of biosensors and facilitate the electron transfer efficiency, so itplay an important role in the construction of biosensors as substrates for biomolecules.In this study, we designed two kinds of electrochemical biosensors based on uraniumspecial DNAzymes and AuNPs to detect uranium in solution.In Chapter2, a label-free electrochemical biosensor based on UO22+specificDNAzymes and [Ru(NH3)6]3+for sensitive and selective detection of uranium wasdescribed. In our experiment, we first designed dsDNA/AuNPs/HDT/Au electrodeand employed CV and EIS for monitoring the processes of the fabrication of thesensor for each step to illustrate the electrochemical properties of the proposed sensor.The DPV method was used for the target analyte with different concentration. Weoptimized the detection conditions, including the hybridization time、 dsDNAincubation time of electrode and pH. We designed dsDNA/Au electrode to futureexplain that using AuNPs can enhance the sensitivity of biosensor. The packingdensities of DNAzymes immobilized both on AuNPs and bare Au electrode weremeasured by electrochemical methods.[Ru(NH3)6]3+/dsDNA/AuNPs/HDT/Auelectrode peak currents decrease with the increase in UO22+concentration from13pMto0.15nM, and the detection limit of5pM.[Ru(NH3)6]3+/dsDNA/Au electrode peakcurrents decrease with the increase in UO22+concentration from0.13~1.27nM, andthe detection limit of0.13nM. The DPV signals of the biosensor slightly changed after adding the metal ions Th4+、Fe3+、Fe2+、Hg2+、Cu2+、Co2+、Pb2+、Ca2+、Mg2+and Zn2+at1nM concentrations. This result indicates that the response of the sensor toUO22+was unaffected by the presence of divalent contaminating ions. Therefore, ourbiosensor was highly selective for UO22+.In Chapter3, a novel highly sensitive and specific electrochemical biosensor fordetecting uranium based on specific DNAzymes and AuNPs is reported. First,1,6hexanedithiol (HDT) was immobilized on the gold electrode surface throughformation self assembled monolayers. To amplify the signal, AuNPs wereimmobilized on the HDT via a thiol Au interaction. Then, the dsDNA waschemi-absorbed to the AuNPs via a3’ terminal thiol. EIS and CV were conducted tomonitor each step of the processes during the biosensor fabrication. The DPV methodwas used for the target analyte with different concentration. The peak currentincreased along with increased UO22+concentration (22pM to0.13nM). The peakcurrent of the sensor was linearly correlated to the target concentration. The linearequation was I/μA=－21.5－196.9c/nM, with the slope of－196.9μA (nM)1for peak current [I and c stand for the peak current and UO22+concentration,respectively]. The detection limit was12pM and the correlation coefficient of was0.994. The DPV signals of the biosensor slightly changed after adding the metal ionsTh4+, Fe3+, Fe2+, Hg2+, Co2+, Pb2+, and Mg2+at1nM concentrations. This resultindicates that the response of the sensor to UO22+was unaffected by the presence ofdivalent contaminating ions. Therefore, our biosensor was highly selective for UO22+.