Label-free fluorescence DNA walker for protein analysis based on terminal protection and dual enzyme assisted cleavage induced G-quadruplex/berberine conformation

Development of a simple, fast, cost-efficient and sensitive approach for accurate protein analysis is of high significance due to its potential application in disease diagnosis and biomedicine research. Thus, we established a label-free fluorescence DNA walker for streptavidin detection based on terminal protection and dual enzyme assisted cleavage induced G-quadruplex/berberine conformation. In this paper, the swing arm probe and report probe were pre-assembled on gold nanoparticles. With the addition of a target, through the high-efficiency affinity between streptavidin and biotin in order to prevent the hydrolysis of exonuclease I, the swing arm probe which contains 8-17 DNAzyme cannot be destroyed and plays a role in the catalytic cleavage of the report probe, and the liberating fragment of the report probe which contains a specific sequence (5'-(TTAGGG)4) of G-quadruplex units can combine with berberine and shows an evident fluorescence signal enhancement. Our method, a sensitive and selective method of protein detection, achieves a 20 pM detection limit toward streptavidin. This developed DNA walker, which combines terminal protection and a dual enzyme assisted strategy, provides a prospective channel for streptavidin detection and should also be used for the design of biosensors in bio-detection and disease diagnosis.