Label-free SERS detection of apolipoprotein A4 based on DNAzyme-driven molecular machine

Apolipoprotein A4 has a wide range of synaptic toxicity and can be used as a reliable molecular biomarker for the detection of depressive disorder. It has certain clinical requirements for simple, rapid and selective detection of apolipoprotein A4. Here, based on the DNA biped walker driven by DNAzyme, we designed a label-free surface-enhanced Raman scatting sensor for rapid detection of apolipoprotein A4. Compared with the typical DNA walker, the biped DNA walker has the advantages of large walking range and high magnification efficiency. The magnesium-dependent DNAzyme drives the DNA walker, which can cut the MBs sequentially. The resulting MBs fragments were then hybridized with AuNPs modified by repetitive adenine to make Au NPs proliferate on the substrate surface, resulting in a large number of cycles. Using 736 cm^-1 adenine as the internal marker, surface enhanced Raman scattering analysis showed that the linear detection range of human apolipoprotein A4 was 10∼1000 ng mL^-1, the detection limit was 4.7 pg/mL, and it had significant specificity, which could meet the needs of clinical detection and showed great application potential.