Enhancing the Stability of Single-Stranded DNA onto Gold Nanoparticles for Molecular Machine through Salt and Acid Regulation
DNA functionalized gold nanoparticles (DNA-AuNPs) have shown great potential and exciting opportunities for constructing machinelike nanodevices. Nonthiolated DNA can be grafted onto gold surfaces via the DNA bases, such as polyadenine (polyA)-DNA. The colloidal stability of polyA-DNA-AuNPs has a significant dependent on salt and pH that affect the assembly of AuNPs and its application in polyA-DNA molecular machine. High salt and low pH value are contributed to stabilize polyA-DNA-AuNPs. In acid condition, adenine can be protonated that enables positively-charged, thus enhances the adsorption of polyA-DNA onto gold surface by electrostatic and coordination of multiple interactions to achieve a high DNA grafting density and colloidal stability. In addition, the length of adenine has an important effect on the efficiency of the DNA machine, while the length of thymine has little effect when thymine length is less or equal to seven. The assembly of AuNPs driven by dynamic polyA-DNA molecular machines is successfully accomplished with A5-DNA and A9-DNA. A moderate concentration of catalyst oligomer (50nM) can improve DNA hybridization efficiency. A9-DNA based molecular machine is more efficient than A5-DNA because of the larger amount of A9-DNA onto AuNPs, which increases the probability of collisions between complementary DNA strands. Therefore, polyA-DNA functionalized nanoparticles can be used as a basic unit to construct assembly ordering structures and accomplish dynamic molecular machines applying in molecular diagnostics field.