pH-Induced Reversible Expansion/Contraction of Gold Nanoparticle Aggregates

DNA nanomotor, based in pH-triggered reversible formation/dissociation of a DNA triplex, was explored by separate functionalization of AuNPs with two 5' thiolated oligonucleotides. The DNA triplex used was pH-sensitive and consisted of 52% C+G- triplets and 48% T-A-T triplets, while 10 nm AuNP aggregates were incubated with thiolated DNA strands over 48 hr. The results show that the interparticle spacings in the AuNP aggregates is different at pH 8.0 and 5.0 and the NPs are closer at pH 5.0 than at pH 8.0. When the solution pH was changed to 8.0 by adding NaOH, the peak of the plasmon band shifted to 524nm, indicating that the interparticle spacing change back, consistent with the dissociation of the DNA triplexes. The results indicate that the DNA-AuNP aggregates could be used as sensors and readouts for the continuous monitoring of the pH value of a flowing solution.