Construction Of ZIF-8 Nanoprobes And Their Use For Imaging Of Tumor Markers MiRNA

MicroRNAs（miRNAs）are short non-coding RNAs with approximately19-23 nucleotides.Studies have shown that mi RNAs are key molecules that regulate cell proliferation,differentiation and apoptosis.Aberrant expression of mi RNAs is closely associated with major diseases such as tumors.Therefore,some characteristic mi RNAs are important biomarkers for cancer diagnosis.The traditional detection methods for cancer-related mi RNAs include Northern blotting,quantitative real-time polymerase chain reaction（q RT-PCR）and microarray technology.The traditional methods have high detection sensitivity and low detection limits,but these methods are only used for homogeneous solutions and cell lysates.In recent years,some novel methods related to the detection of intracellular mi RNAs have been developed.For example,functional nucleic acids and fluorescent nanosensors based on nanomaterials are used to detect mi RNAs in cells.Therefore,focuses on the use of functional nucleic acids such as nucleic acid molecular beacons as target mi RNA recognizers as well as signal units,combined with nanomaterials to construct a series of fluorescent nanoprobes for mi RNA detection.The details are as follows:（1）A DNA nanosensor（ML@ZIF-8）was constructed for intracellular mi RNA imaging.The probe ML@ZIF-8 was constructed by encapsulating DNA double-stranded structures（ML）in biomineralized zeolitic imidazolium backbone-8 nanoparticles（ZIF-8 NPs）,where ML is composed of a locking strand（L）and molecules beacon（MB,5’end-labeled fluorophore Cy5,3’end-labeled fluorophore Cy3）.After cellular internalization,ML@ZIF-8nanoparticles release ML into the cytoplasm and undergo a chain substitution reaction with the target mi RNA（let-7a）,releasing MB beacon molecules and inducing fluorescence resonance energy transfer to occur,and detect let-7a in cells by fluorescence signal changes.This nanosensor provides a novel and effective strategy for cancer diagnosis.Based on the above basis,the study continued with the adsorption of nucleic acid double strand（ML）on the surface of ZIF-8 to form a fluorescent nanoprobe（ZIF-8@ML）for intracellular mi RNA imaging.（2）A DNA nanofluorescent sensor（Zr-B@ZIF-8）was constructed for intracellular mi RNA imaging.In this nanosensor,the 5’end of the DNA molecular beacon is labeled with a fluorescent moiety（FAM）and the 3’end with a burst moiety（BHQ1）,which acts as a target recognizer and signal producer,and Zr⁴⁺forms nanoparticles（Zr-B）by ligand self-assembly.The synthesized Zr-B nanosensor was mineralized by a layer of ZIF-8 to produce a new nanostructure（Zr-B@ZIF-8）.After cellular internalization,beacons from Zr-B@ZIF-8 nanoparticles will be released into the cytoplasm to react specifically with the target mi RNA（mi RNA-21）and promote fluorescence recovery.Hybrid nanosensors provide a simple and versatile strategy for diagnostic applications.