Acid-triggered nucleic acid release from gold nanoparticles via Schiff base linkages: In vitro validation of...

Gold nanoparticles with brush structures of nucleic acid drugs (Nuc-AuNPs) are prepared by mixing thiol-modified nucleic acid drugs and AuNPs due to the strong affinity of the Au-S bond. However, effectively regulating the intracellular kinetics of nucleic acids remains a challenge in achieving highly efficient nucleic-acid delivery. In this study, we designed new DNA-Schiff-AuNPs. The DNA release behaviors of these DNA-modified AuNPs were characterized under acidic conditions analogous to those in intracellular endosomes. Cy5-labeled DNA with an amine terminus (Cy5-DNA-NH₂) reacted with 4-mercaptobenzaldehyde in dimethyl sulfoxide to form a Schiff base. The resulting Cy5-DNA-Schiff-SH was added to the AuNP dispersion system to prepare Cy5-DNA-Schiff-AuNPs. These nanoconjugates were characterized by fluorescence spectroscopy. In the appropriate buffer, the fluorescence intensity of AuNPs remained constant at pH 7.4, while exhibiting an approximately four-fold increase at pH 4.0 and 5.0. In addition, a drastic color change from red to blue was observed after 24 h, suggesting that DNA was released from AuNPs at a pH of 5.5. The DNA-Schiff-AuNPs were effectively incorporated into HeLa cells without any toxicity. Furthermore, siRNA-AuNPs incorporating Schiff base linkages demonstrated significantly enhanced suppression of epidermal growth factor receptor gene expression compared to conventional siRNA-AuNPs. These findings highlight the potential of Schiff base-linked Nuc-AuNPs as a promising platform for intracellular nucleic acid delivery.