Development Of SERS Substrates And Biosensors For UO 2 2+ Detection

Uranium is a main part of nuclear materials as well as the main origin of the nuclear wastes. Human beings have a high chance of being exposed to the circumstance of uranium, which can cause long-term health damage. Thus developing detecting methods of uranium becomes a hot topic. Developing detection techniques with high sensitivity is also the aim of analysis field. Because of it's merits of high efficiency, resolution and sensitivity, Surface-Enhanced Raman Spectrum (SERS) technique has been widely used as a powerful analysis tool for a variety of research fields. Enzyme-free amplification technique is another ultrasensitive sensing technique due to the advantanges of simple, high efficiency and low cost. Through combination with other detecting methods, enzyme-free amplification technique are widely used for the design of ultrasensitive biosensors. In this paper, in order to realize the detection of uranly, several kinds of SERS substrates were prepared by self-assembly method, and an UO22+ electrochemical biosensor was proposed through combining the UO22+-specific DNAzymes and hybridization chain reaction (HCR) amplication. The main contents include:1. A facile self-assembly strategy for fabricating silver nanoparticles (AgNPs) arrays on the no-modified surface of silicon wafers with ascorbic acid (Vc) as an active reagent within one hour was proposed. The effect of Vc and deposition time on the performance of SERS substrates was systematically studied. The nanochain structure of AgNPs arrays exhibits excellent SERS signals, and shows an excellent EF as high as 3.65 × 108. The best prepared SERS substrate shows a good reproducibility. The whole self-assembly process of AgNPs only need 1 hour. What's more, gold nanopartcles were self-assembled on the glass substrate modified with APTMS. The treatment of acid on the APTMS modified glass substrate for protonation promoted the self-assembly of AuNPs. The effect of the size of gold nanoparticles on SERS intensities was investigated. The result showed that the substrate of self-assembly of a larger size of gold nanoparticles produced a stronger SERS EF.2. The SERS spectrums of UO22+ were obtained by using the assembly AuNPs and AgNPs SERS substrates to detect uranyl nitrate. The symmetric stretching vibration peak of UO22+ is 860 cm-1 on the surface of AuNPs substrate and 719 cm-1 on the surface of AgNPs substrate. The interactions between uranyl and SERS substrate cause the peak of uranyl shift to low wave number direction. Silver nanoparticles (AgNPs)/graphene complex substrate, was designed to prevent the interation between SERS substrate and analyte by using the inert graphene layer. The morphology of complex substrate was obtained by SEM. The Raman peak that appeared around 771 cm-1 is considered to be the symmetric stretching mode of UO22+, shifting back about 52 cm-1 to high wave number direction when compared with AgNPs substrate. The result indicates that graphene layer isolates the interaction between AgNPs substrate and uranyl in some degree.3. A novel strategy for ultrasensitive detection of UO2+ was proposed by using a UO22+ -specific DNAzyme and two free labeled DNA hairpins. In the presence of UCO22+, the cleaved strand DNA produced by the DNAzyme catalytic cleavage of S-DNA triggers the hybridization chain reaction between two alternating hairpin DNA structures to form a nicked double-helix DNA polymers on the electrode surface. The concentration of UO22+ is indirectly determined by monitoring the change of the electrochemical signal of MB intercalated into the minor groove of the long dsDNA polymers. The principle and detection processes of this electrochemical biosensor for amplification detection of UO22+ were described. The detection conditions of the biosensor, such as the concentration of hairpins, pH and the incubation time of HCR, were optimized. Under optimal conditions, this biosensor demonstrates a high sensitivity of UO22+ detection with the dynamic concentration range spanning from 0.05 to 4 nmol/L and a detection limit of 20 pmol/L.