Hao Wu,Kai Zhang,Yaling Liu,Hongyong Wang,Jun Wu,Feifan Zhu,Pei Zou
In this work, a new binding-induced and label-free colorimetric method for protein detection has been developed on the basis of an autonomous assembly of hemin/G-quadruplex DNAzyme amplification strategy. The system consists of two proximity probes carrying two aptamer sequences as recognition elements for target, and two hairpin structures include three-fourths and one-fourth of the G-quadruplex sequences in inactive configuration as functional elements. In the presence of target protein, two proximity probes bind to the protein simultaneously, forming a stable DNA–protein complex. Then the complex triggers an autonomous cross-opening of the two functional hairpin structures, leading to the formation of numerous hemin/G-quadruplex DNAzymes. The resulting DNAzymes catalyze the oxidation of colorless 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS 2− ) to the green-colored ABTS •− with the presence of H 2 O 2 , thus providing the amplified colorimetric detection of target. Using human α-thrombin as the protein target, this binding-induced DNAzyme amplification colorimetric method affords high sensitivity with a detection limit of 1.9 pM. Furthermore, this method might be further extended to sensitive detection of other proteins by simply replacing recognition elements of proximity probes.
A biosensing system is established for the multi-amplified detection of DNA or specific substrates of aptamers under isothermal conditions , which combines nicked rolling circle amplification (N-RCA) and beacon assisted amplification (BAA) with sensitive colorimetric technique by using DNAzymes as reporter units. According to the configuration, the analysis of DNA is accomplished by recognizing the target to capture nucleic acid-functionalized magnetic particles, followed by the self-assembly of the other two nucleic acids into multicomponent DNA supramolecular structure on magnetic particles. After magnetic separation, the circularization with ligase and the fragmentation with polymerase activate N-RCA and BAA in the presence of polymerase, dNTPs , and the nicking endonuclease , successively producing horseradish peroxidase (HRP)-mimicking DNAzymes that act as colorimetric reporter to catalyze the oxidation of ABTS 2− by H 2 O 2 in the presence of hemin . Under the optimized conditions, we obtain a wide dynamic range for DNA analysis over 6 orders of magnitude from 1.0×10 −14 to 1.0×10 −9 M with a low limit of detection of 6.8×10 −15 M. In the absence of a target, neither self-assembly of nucleic acids nor amplification process can be initiated, indicating an excellent selectivity of the proposed strategy. Similarly, an analogous system is activated by cancer cells or lysozyme through cooperative self-assembly of nucleic acids on magnetic particles in the presence of respective substrates of aptamers to synthesize HRP-mimicking DNAzymes that give the readout signal for the recognition events, achieving LODs of 81 Ramos cells and 7.2×10 −15 M lysozyme, respectively.
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