Heterogeneous immunoassay based on
magnetic separation is commonly
used in inductively coupled plasma-mass spectrometry (ICP-MS)-based
biomedical analysis with elemental labeling. However, the functionalized
magnetic beads (MBs) often suffer from non-specific adsorption and
random distribution of the functional probes. To overcome these problems,
DNA tetrahedron (DT)-functionalized MBs were designed and further
conjugated with substrate modified Au NPs (Sub-AuNP). Based on the
prepared MB-DT-AuNP probes, an MB-DT based multicomponent nucleic
acid enzyme (MNAzyme) system involving Au NPs as the elemental tags
was proposed for highly sensitive quantification of miRNA-155 by ICP-MS.
Target miRNA would trigger the assembly of MNAzyme, and Sub-AuNP would
be cleaved from the MB-DT-AuNP probe, resulting in a cyclic amplification.
Single-stranded DNA-functionalized MB (MB-ssDNA)-AuNP probes were
prepared as well. Comparatively, the amount of Au NPs grafted onto
MB-ssDNA-AuNP probes was higher than that grafted onto MB-DT-AuNP
probes. Meanwhile, a higher signal-to-noise ratio was obtained by
using MB-DT-AuNP probes over MB-ssDNA-AuNP probes in the MNAzyme system.
Under the optimal experimental conditions, the limit of detection
for target miRNA obtained by using MB-DT-AuNP probes was 1.15 pmol
L–1, improved by 23 times over that obtained by
the use of MB-ssDNA-AuNP probes. The proposed MB-DT-MNAzyme-ICP-MS
method was applied to the analysis of miRNA-155 in serum samples,
and recoveries of 86.7–94.6% were obtained. This method is
featured with high sensitivity, good specificity, and simple operation,
showing a great application potential in biomedical analysis.