Modular Engineering of a DNA Tetrahedron-Based Nanomachine for Ultrasensitive Detection of Intracellular Bioactive Small Molecules.

Bioactive small molecules serve as invaluable biomarkers for recognizing modulated organismal metabolism in correlation with numerous diseases. Therefore, sensitive and specific molecular biosensing and imaging in vitro and in vivo are particularly critical for the diagnosis and treatment of a large group of diseases. Herein, a modular DNA tetrahedron-based nanomachine was engineered for the ultrasensitive detection of intracellular small molecules. The nanomachine was composed of three self-assembled modules: an aptamer for target recognition, an entropy-driven unit for signal reporting, and a tetrahedral oligonucleotide for the transportation of the cargo (e.g., the nanomachine and fluorescent markers). Adenosine triphosphate (ATP) was used as the molecular model. Once the target ATP bonded with the aptamer module, an initiator was released from the aptamer module to activate the entropy-driven module, ultimately activating the ATP-responsive signal output and subsequent signal amplification. The performance of the nanomachine was validated by delivering it to living cells with the aid of the tetrahedral module to demonstrate the possibility of executing intracellular ATP imaging. This innovative nanomachine displays a linear response to ATP in the 1 pM to 10 nM concentration range and demonstrates high sensitivity with a low detection limit of 0.40 pM. Remarkably, our nanomachine successfully executes endogenous ATP imaging and is able to distinguish tumor cells from normal ones based on the ATP level. Overall, the proposed strategy opens up a promising avenue for bioactive small molecule-based detection/diagnostic assays.