Endonuclease-driven DNA walking for constructing a novel colorimetric and electrochemical dual-mode biosensing method

Enhancement of telomerase extension via quadruple nucleic acid recycling to develop a novel colorimetric biosensing method for kanamycin assay

BACKGROUND

Colorimetric biosensors have important value for antibiotic residue testing. However, many previous methods were constructed based on the optical density change of certain unstable single-colored products with poor discrimination for visual measurements. Moreover, their low extinction coefficients usually result in low sensitivity of biosensors. In addition, many conventional signal amplification strategies often involve sophisticated nanomaterial preparation, inconvenient multi-step assay manipulation and limited signal amplification ability. Therefore, the development of new colorimetric biosensing strategies with excellent visual discrimination, high sensitivity and convenient manipulation is highly desirable.

RESULTS

We designed a target recycling accelerated cascade DNA walking amplification mechanism to trigger a telomerase extension-related enzymatic reaction, and developed a novel colorimetric biosensing strategy for kanamycin (Kana) assay. The target recycling was induced by an exonuclease III-assisted aptamer recognition reaction, which could also trigger the successive DNA walking at the streptavidin (SA)- and magnetic bead (MB)-based tracks. This not only caused the quantitative exposure of the telomeric substrate primers on MB surfaces but also released another strand to accelerate the SA-based DNA walking. By using the telomerase extension product to link numerous alkaline phosphatases and induce the plasmonic property change of gold nanobipyramids (Au NBPs), a colorimetric signal output strategy was constructed. This method could be applied for the high-resolution visual screening of Kana, and it also showed a very low detection limit of 17.6 fg mL-1 for assaying Kana over a wide, five-order-magnitude linear range.

SIGNIFICANCE

The quadruple nucleic acid recycling-enhanced telomerase extension resulted in the ultrahigh sensitivity of the method and also excluded the sophisticated manipulations involved in conventional biosensing strategies. The multiple enzyme catalysis-induced plasmonic property change of Au NBPs realized the stable and multicolor visual signal transduction. Together with its low cost, simple operation, high selectivity, excellent repeatability, and reliable performances, this method exhibits great potential for use in practical applications.

Dual cascade DNA walking-induced "super on" photocurrent response for constructing a novel antibiotic biosensing method

The construction of effective methods for the convenient testing of antibiotic residues in real samples has attracted considerable interest. Herein, we designed a dual cascade DNA walking amplification strategy and combined it with the controllable photocurrent regulation of a photoelectrode to develop a novel photoelectrochemical (PEC) biosensing method for antibiotic detection. The photoelectrode was prepared through the surface modification of a glassy carbon electrode with the TiO₂/CdS QDs nanocomposite synthesized by an in situ hydrothermal deposition method. The strong anodic PEC response of the nanocomposite could be well inhibited by the introduction of a silver nanoclusters (Ag NCs)-labeled DNA hairpin onto its surface. Upon the target biorecognition reaction, an Mg²⁺-dependent DNAzyme (MNAzyme)-driven DNA walking was triggered to release another MNAzyme strand-linked streptavidin (SA) complex. As this SA complex could serve as a four-legged DNA walker, its cascade walking on the electrode surface not only released Ag NCs but also caused the linking of Rhodamine 123 with the electrode to realize the "super on" photocurrent output. By using kanamycin as the model analyte, this method showed a very wide linear range from 10 fg mL^-1 to 1 ng mL^-1 and a very low detection limit of 0.53 fg mL^-1. Meanwhile, the simple photoelectrode preparation and the aptamer recognition-based autonomous DNA walking resulted in the convenient manipulation and excellent repeatability. These unique performances determine the great potential of the proposed method for practical applications.

CuS quantum dots activated DNAzyme for ratiometric electrochemical detection of telomerase activity

Telomerase activity detection has attracted much attention concerning its importance for early cancer diagnosis. Here, we established a ratiometric electrochemical biosensor for telomerase detection based on CuS quantum dots (CuS QDs) dependent DNAzyme-regulated dual signals. The telomerase substrate probe was used as the linker to combine the DNA fabricated magnetic beads and CuS QDs. In this way, telomerase extended the substrate probe with repeated sequence to from hairpin structure, releasing CuS QDs as an input to DNAzyme modified electrode. DNAzyme was cleaved with high current of ferrocene (Fc) and low current of methylene blue (MB). On the basis of the obtained ratiometric signals, telomerase activity detection was achieved in the range of 1.0 × 10^-12-1.0 × 10^-6 IU/L, with the limit of detection down to 2.75 × 10^-14 IU/L. Moreover, telomerase activity from HeLa extracts was also tested to verify the clinical application.