Development Of Ultrasensitive DNA Detection Based On The Optical Nanomaterials

DNA detection not only is an important approach in molecular biology and biomedicine,but is a critical technique in the identification of pathogenic microorganism in food and thetest of food component and even the detection of over-growing GMOs. Nanomaterials, as tothe excellent optical properties, physicochemical properties and good biocompatibility,become more and more popular. Nanotechnology can combine with PCR to build novelprinciple and new methods for rapid, ultrasensitive and high-throughput DNA detection.First, two differently sized Au NPs were synthesized, which had uniform morphology,excellent dispersity and good stability. Forward and reverse primers were respectivelymodified on the surface of large and small Au NPs. Asymmetric PCR was performed on thesurface of large and small Au NPs modified with distinct amount of primers, while symmetricPCR was performed on Au NPs surface with the same amount of primers. Chiralsuperstructures with distinct structural characteristics were respectively assembled underasymmetric and symmetric PCR. The spatial configuration of superstructures at differentcycles was reconstructed through tomography, which was convenient for the analysis of therelationship between structures and chiral changes. The origin of chirality was preliminarilyanalyzed. PCR-based assembly indeed pioneered a new platform for the fabrication of chiralmaterials.Second, two forward and reverse primers were precisely modified on the surface of largeand small Au NPs. Under optimized condition, heterochains were successfully assembled bylarge and small Au NPs. The chirality of PCR products at different cycles was explored. Withthe increasing length of heterodimers, the chiral signal was correspondingly enhanced.Chiral-based DNA detection was first built depending on the strong chirality of PCR products,and a limit of detection was as low as to71.2aM. PCR-based assembly with strong chiralitysuccessfully achieved rapid, low cost and ultrasensitive DNA detection. Compared to theultraviolet absorption, chiral signal showed excellent sensitivity and flexibility. A novelprinciple of chiral-based DNA detection was first developed.Third, only one forward and reverse primer was respectively modified on the surface oflarge and small Au NPs, heterodimers were largely assembled through PCR and the yield at20cycles reached up to78.9%. Heterodimers showed chirality at525nm. Silver and goldshell with distinct thickness was respectively deposited on the surface of heterodimers, andthe chiral signals exhibited obvious shift in the range of418nm to586nm. And then, asecond gold and silver shell was further deposited on the surface of dimers@Ag anddimers@Au core-shell structures, the chirality of dimers@Ag@Au and dimers@Au@Agcore-shell-shell structures called backed to525nm, achieving the reversible control ofchirality. After calculation, g-factor of dimers@Au core-shell structures was highest andreached up to1.21×10-2. PCR-based dimers@Au core-shell structures with excellent chiralityapplied in the DNA detection, and a limit of detection was as low as to1.0copy. Chiral-basedsingle DNA detection was for the first time established.Forth, a silver shell with increasing thickness was deposited on the surface of large and small Au NPs. Only one primer was modified on the surface of Au@Ag core-shell NPs. Andthen, Au@Ag core-shell heterodimers were assembled through PCR. The chirality of Au@Agcore-shell heterodimers with different silver shell thickness but a well-fined amplificationlength of primers was exploited. With the increasing thickness of silver shell, the chiral signalof Au@Ag core-shell heterodimers was correspondingly enhanced but showed no obviousshift. Keeping a certain silver shell thickness, the chirality of Au@Ag core-shell heterodimersat distinct amplification length of primers could be further exploited, which would have apotential application for the DNA length detection.Finally, QDs encoded SiO2NPs were successfully prepared. The encoded NPs showeduniform structures and excellent fluorescence coding and strong fluorescence signal. Throughthe decoding of the multiplex fluorescence spectra, QDs encoded SiO2NPs were fuetherapplied in four different GMOs detection, and a limit of detection was as low as to4.48fM.This method played a tutorial significance for high-throughput DNA detection.