Environmental and intercellular Pb2+ ions determination based on encapsulated DNAzyme in nanoscale metal-organic frameworks

With the merits of low cost, simple synthesis procedure, and high affinity for metal ions, deoxyribozyme (DNAzyme) have played important roles in metal ions detection. However, the intracellular applications of DNAzyme are limited because of enzymatic degradation and inefficient cellular uptake. To address these problems, GR-5 as model DNAzyme was encapsulated into zeolitic imidazolate frameworks-8 (ZIF-8) nanoparticles by biomimetic mineralization. The positively charged ZIF-8 with high DNAzyme loading capacity retained their ability to enter cells. Compared with free DNAzyme, the biomimetic mineralization synthesis method has greatly improved the stability of pristine DNAzyme. The as-synthesized DNAzyme@ZIF-8 composite exhibited good stability resisting DNase I, and was used as a sensitive fluorescent nanoprobe for Pb 2+ determination and successfully achieved selective and sensitive determination for Pb 2+ at λ ex / λ em  = 494/522 nm in real samples. The linear range for the determination of Pb 2+ is 50 to 500 nM. Moreover, the highly active DNAzyme delivered by ZIF-8 allows noninvasive imaging of Pb 2+ measurement in living cells. This strategy will extend the suitability of functional nucleic acids for in vitro and in vivo bioanalysis and bioimaging. Graphical abstract