Optical Properties And Application Of DNA-Noble Metal Nanoclusters

In recent decades,DNA-noble metal nanoclusters,as a new type of fluorescent nanomaterial,have attracted wide attention of researchers due to their properties of small size,adjustable fluorescence emission wavelength,low toxicity and good biocompatibility.In this study,the fluorescent DNA-Ag NCs,DNA-Au/Ag NCs and DNA-Cu/Ag NCs were successfully prepared using C-AGRO100,C-T30695 and C-TB C-rich ss DNA as the templates,and these ss DNA were the complementary sequences of the well-known AGRO100,T30695,and TB G-rich sequences,respectively.Their UV-visible absorption and fluorescence spectra were measured.We investigated the effects of template DNA sequence and Au/Cu doping on the fluorescence properties of DNA-Ag NCs by comparing the fluorescence properties of different template DNA-Ag NCs and the same template DNA-Ag NCs,Au/Ag NCs,Cu/Ag NCs.Then,The C-AGRO100-Au/Ag NCs which had better fluorescent intensity and well stability were selected to further study the effects of ethanol in PBS and temperature on its fluorescence properties.In addition,the effects of G-rich sequences on the fluorescence properties of DNA-Ag NCs and DNA-Cu/Ag NCs prepared with different templates were also investigated.The main results were as follows:(1)We first used three different C-rich sequences of DNA as templates to prepare the corresponding DNA-Ag NCs,DNA-Au/Ag NCs and DNA-Cu/Ag NCs,and their UV-visible absorption and fluorescence spectra were measured.The results showed that the fluorescence properties of the same type of DNA-metal nanoclusters formed with different DNA templates were different,and the fluorescence properties of different kinds of DNA-metal nanoclusters synthesized by the same DNA templates were also different.Compared with DNA-Ag NCs,the fluorescence stability of DNA-Au/Ag NCs is greatly improved and has a large Stokes-shift;DNA-Cu/Ag NCs have stronger fluorescence and the fluorescence stability is slightly improved.Finally,the C-AGRO100-Au/Ag NCs with bright orange fluorescence and well stability were selected to further study the effects of different volume fraction of ethanol in PBS and temperature on its fluorescence properties.(2)The effects of ethanol volume fraction in PBS and temperature on the fluorescence properties of C-AGRO100-Au/Ag NCs were investigated.The results showed that the fluorescence intensity gradually increased with increasing volume fraction of ethanol and the maximum fluorescence intensity appeared when the volume fraction of ethanol was 70%,following that the fluorescence intensity rapidly decrease as the volume fraction of ethanol increased from 80% to 100%.TEM images and DLS spectra indicated that proper ethanol could improve the dispersity of C-AGRO100-Au/Ag NCs in PBS and enhanced its fluorescence intensity,while the high concentration of ethanol induced the aggregation of C-AGRO100-Au/Ag NCs to cause its fluorescence quenching.In addition,the C-AGRO100-Au/Ag NCs displayed remarkable temperature-dependent fluorescent property.The fluorescence responses were reversible between 5 °C and 70 °C and linear to the temperature ranges from 5 to 30 °C and from 30 to 70 °C,with the related coefficient of 0.992 and 0.993,respectively.(3)A G-rich sequence was added to the 3' end of C-AGRO100-,C-TB-and C-T30695-DNA to form new DNA templates for the synthesis of corresponding DNA-Ag NCs and DNA-Cu/Ag NCs.The effects of G-rich sequences on the fluorescence properties of DNA-Ag NCs and DNA-Cu/Ag NCs formed with different templates were investigated.The results showed that the terminal G-rich sequence could enhanced the red fluorescence intensity of DNA-Ag NCs and DNA-Cu/Ag NCs,and the enhancement effect of DNA-Cu/Ag NCs is more remarkable than DNA-Ag NCs.