Design of pH-Tunable Reversible DNA Nanostructures for Efficient Drug Delivery

Abstract The development of stimuli-responsive nanocarriers has emerged as a promising strategy for improving the precision and efficacy of drug delivery systems. Among these, DNA nanostructures offer unique advantages owing to their inherent programmability, biocompatibility, and precise structural tunability. Although three-dimensional DNA nanostructures, such as DNA tetrahedrons, have been reported to undergo pH-driven disassembly for applications in drug delivery and cargo protein release, their structural design permits only partial disassembly and impedes reversible regulation, thereby limiting their broader applications. Here, we report the rational design of a pH-tunable DNA tetrahedron (pHTd) through the strategic incorporation of an i-motif, enabling assembly at physiological pH and disassembly under acidic conditions, thereby exhibiting reversible structural transitions in response to pH changes. The pHTd displayed promising serum stability with negligible cytotoxicity. Furthermore, pHTd loaded with the anticancer drug Doxorubicin (Dox) exhibited enhanced cytotoxicity compared with free Dox, accompanied by efficient cellular uptake, highlighting its potential as a smart drug delivery platform. In addition, we demonstrate DNA nanostructures including a tetrahedron (pHTd-2), a triangle (pHT), and a square (pHS) that exhibit contrasting pH-responsive behaviors, collectively representing a Janus-like system with opposite structural responses to a common pH stimulus. Collectively, this work establishes a general framework for engineering reversible pH-responsive DNA nanostructures and broadens their potential applications in targeted drug delivery, bioimaging, and logic-gated nanodevices.