BCL-2 gene as well as its products is recognized as a promising target for the molecular targeted therapy of tumors. However, due to certain defense measures of tumor cells, the therapeutic effect based on the gene silencing of BCL-2 is greatly reduced. Here we fabricate a smart response nucleic acid therapeutic that could silence the gene effectively through a dual-targeted and cascade-enhanced strategy. In brief, nano-graphene oxide (GO), working as a nano-carrier, is loaded with a well-designed DNAzyme, which can target and silence the BCL-2 mRNA. Furthermore, upon binding with the BCL-2 mRNA, the enzymatic activity of the DNAzyme can be initiated, cutting a substrate oligonucleotide to produce an anti-nucleolin aptamer AS1411. Nucleolin, a nucleolar phosphoprotein, is known as a stabilizer of BCL-2 mRNA. Via binding and inactivating the nucleolin, AS1411 can destabilize BCL-2 mRNA. By this means of simultaneously targeting mRNA and its stabilizer in an integrated system, effective silencing of the BCL-2 gene of tumor cells is achieved at both the cellular and in vivo levels. After being dosed with this nucleic acid therapeutic and without any chemotherapeutics, apoptosis of tumor cells at the cellular level and apparent shrinkage of tumors in vivo are observed. By labeling a molecular beacon on the substrate of DNAzyme, visualization of the enzymatic activity as well as the tumor in vivo can be also achieved. Our work presents a pure bio-therapeutic strategy that has positive implications for enhancing tumor treatment and avoiding side effects of chemotherapeutics.

Despite the progress on the analysis of miRNA either in vitro or in vivo, intracellular imaging of lowly expressed microRNA remains a challenge. Here we develop a novel dual-enzyme-propelled DNA walking nanomachine, which is tailored to accomplish this mission. The nanomachine is constructed with nanoparticles-loaded DNA tracks, on which the targeted miRNA working as a single-foot DNA walker can move autonomously under the catalysis of two cooperative enzymes. Cleavage of the DNA tracks like a "burnt-bridge" mechanism is thereafter triggered, resulting in an amplified fluorescent signal. After the comprehensive study and optimization of the DNA nanomachine, miR-892b, a significantly down-regulated miRNA in breast cancer cells, is selected as a model target. Sensitivity detection in vitro is achieved with a superior detection limit of 4 pM. While being delivered into cells, the DNA nanomachine is available for the imaging of the lowly expressed microRNA, which is totally missing using the conventional fluorescence in situ hybridization (FISH) method. Up-regulation or down-regulation of the miRNA by exogenous regulatory factors can be also well evaluated. This DNA nanomachine provides a competitive approach for the analysis of miRNA, and has the potential to be extended to some other biomolecules.