Ultrasensitive DNAzyme based amperometric determination of uranyl ion using mesoporous silica nanoparticles loaded with Methylene Blue

The authors describe an ultrasensitive amperometric enzymatic assay for uranyl ion. It is based on the use of mesoporous silica nanoparticles (mesoSiNPs) loaded with Methylene Blue (MB) and functionalized with an UO2(II)-dependent DNAzyme. The electroactive label MB was sealed in the inner pores of the mesoSiNPs along with double stranded DNA (containing the DNAzyme and the substrate strand). In the presence of UO2(II), the DNAzyme is actived to cleave the substrate strands. This leads to the cleavage of the caps and the release of MB from the mesoSiNPs. The amount of released MB depends on the concentration of UO2(II) and can be determined amperometrically, best at a working voltage of -0.25 V (vs SCE), by using a chitosan coated carbon paste electrode. Response is linear in the 20 pM to 0.1 nM UO2(II) concentration range, and the detection limit is as low as 0.15 pM. Recoveries from spiked samples varied from 91.3 to 99.4%. The assay is highly specific, selective, and not interfered by other metal ions.